favourite immune cell assignment: mast cell

Favourite Immune Cell Assignment

BIOL 4931 – Immunology

Samantha Bray

December 1st, 2015

Q1-1: What is your favourite cell of the immune system?

The mast cell is my favourite cell of the innate immune system.

Q1-2: In what organ(s) do you find these cells?

Mast cells can be found in most tissues because they circulate in the blood stream and

distribute through the body. They are found in abundance in areas susceptible to pathogens from

the external environment such as the skin, gastrointestinal tract and lungs.1

Q1-3: Find a micrograph of your cell and label its cell structures.

Figure 1. Mast cell electron micrograph.2

Q2-1: How does your favourite cell interact with the human microbiome?

If the bacteria in the human microbiome become pathogenic mast cells act to kill them.

To kill pathogenic microbes mast cells use produce reactive oxygen species and/or antimicrobial

peptides. Another common method used by mast cells to kill pathogenic microbes is engulfing

the microbe through phagocytosis.1

Q2-2: Has your favourite cell been implicated in dysbiosis?

Yes, mast cells are involved when bacteria enter a state of dysbiosis. When normally

benign microbes proliferate to levels that become pathogenic mast cells traffic to the area

infected via the circulatory system and releases granules and cytokines that act to kill the

pathogenic microbes.1

Q2-3: Can your immune cell respond to antigens?

Mast cells have high affinity IgE receptors on their surface that when stimulated by

antigens bound to IgE causes the cell to degranulate emptying histamine, heparin, other enzymes,

and cytokines that attract other immune cells (leukocytes, macrophages) to the site of infection in

order to combat/kill pathogen in the site of infection.1

Q3-1: From what HSC lineage is your favourite cell derived?

Mast cells are from the myeloid lineage of hematopoietic stem cells.3

Q3-2: In what location does the ultimate differentiation of your favourite cell occur?

Mast cells are made in the bone marrow and leave as undifferentiated cells. They travel

through the blood to a tissue where they will differentiate and then reside as mature mast cells.3

Q3-3: Using http://web.expasy.org/cellosaurus/ (or similar resource), find a human cell line

representative of your favourite cell type.

Figure 2. Human mast cell 1 cell line.4

Q4-1: What innate immune sensors are expressed in your favourite cell?

Mast cells express high amounts of high-affinity IgE receptors on their surface. This

receptor binds IgE class antibodies that trigger the cell to degranulate and contributes to allergic

reaction.5 They express TLRs 1-9 that detects intracellular or extracellular pathogens usually of

bacterial or viral origin.6

Q4-2: Does your cell express MHC molecules?

Yes, mast cells express MHC class I and class II molecules on their cell surface that

present antigenic peptide.6

Q4-3: Does your cell interact with the BcR or TcR complex?

Yes, studies have shown that mast cells are able to present antigenic peptide to TcR

complex on T cells. They are able to induce clonal expansion of T cells and migration of T cells

to the lymph nodes to induce an immune response.6

Q5-1: Does your favourite cell interact with DCs?

Mast cells indirectly interact with dendritic cells by releasing cytokines that regulate

dendritic cell migration, maturation and activation. Mast cells release TNF that causes the up

regulation of MHC class II, CD80, CD86 and CD40 on the cell surface facilitating functional

maturation. They also release IL-1, IL-16, IL-18 and CCL5, which promote the migration of

dendritic cells.6 In more recent examples, DC and mast cells have shown direct cell to cell

interactions that last for minutes. Broadly speaking, mast cells and DCs form synapses using the

integrin protein. The synapse then facilitates passage of internalized mast cell antigen to DCs that

then present the antigen on their surface leading to the activation of T cells.7

Q5-2: Is co-stimulation involved in the activation of your favourite cell?

Mast cells express the FcεRI-IgE and the c=Kit (CD117) receptors. When FcεRI and KIT

receptors are co stimulated by antigen the mast cells are triggered to release their granules,

produce more cytokines and promotes cytokine mRNA synthesis. Mast cells can also be co-

stimulated by TLRs, NLRs, CLRs. For example, TLR-2 and TLR-4 signaling combines with

FcεRI receptor signaling to enhance the release of granules and mediators.8 Additionally, C3a

and C5a through the C3aR and C5aR (CD88) can activate mast cells. Mast cells can also be

activated by nerve growth factors such as TRKA, and by IgG through the FcγRI. The co

stimulation of all these receptors determines the extent and pattern of the immune response

produced by mast cell.9

Q5-3: Is your cell’s function influenced by CD4+ T cells.

Yes, CD4+ T cells influence mast cells degranulation. Specifically, CD4+ CD25+ T

regulatory cells influence mast cell degranulation. These T regulatory cells have OX40 receptors

that bind to mast cells OX40 ligand. Through these interactions T regulatory cells cause increased

levels of cAMP and decreased calcium influx inhibiting mast cell degranulation. When

researchers antagonized cAMP allowing the levels to decrease, calcium levels returned to normal

allowing the mast cell to degranulate.10

Q6-1: Does your favourite cell form MTOCs?

Yes, mast cells do form MTOCs. Mast cells use MTOCs for granule secretion. Upon

stimulation of mast cell IgE receptors intracellular calcium levels rise. Syt, a lysosomal sensor,

detects calcium rise and initiates granule mobilization towards the MTOC. From the MTOC, the

granule attaches to kinesin, a motor protein, and moves along the microtubule towards the cells

plasma membrane. It then detaches and fuses with the membrane releasing the granule that

contains histamine, heparin, and serotonin.11

Q6-2: What are the major signalling cascades initiated when your cell is activated?

The major signalling cascade initiates when the mast cell FcεRI (IgE receptor) becomes

activated. Upon IgE binding to FcεRI tyrosine kinases FYN LYN and SYK phosphorylate

NTAL. Through downstream signaling events NTAL activates PI3K that activates both PLCγ

and S1P which both act to mobilize calcium. NTAL also causes activation of MAPK pathway.

The MAPK pathway, P13K, as well as the mobilization of calcium signaling all integrate and

cause the mast cell to degranulate.12

Q7-1: What cytokines are produced by your favourite cell of the immune system?

Mast cells produce many cytokines IL-6, IL-8, TNF, IFNγ, VEGF, MCP-1, etc. They

produce TNF in response to TLR-4 activation by bacterial LPS. LPS can also trigger release of

IL-5, IL-10, and IL-13. Mast cells can also produce IFN in response to double stranded viral

RNA activating TLR-3.13

Q7-2: What cytokines receptors are expressed by your favourite cell of the immune system?

Mast cells may express cytokine receptors IL-3R, IL-4R, IL-5R, IL-9R, IL-10R, IFN-γR.

These cytokine receptors modulate mast cells immune response. For example, IL-4 up regulates

the expression of FcεRI on mast cell surface. IL-5 causes the proliferation of mast cells (in the

presence of SCF), and IFN-γ down regulates the population of mast cells.14

Q7-3: What chemokines attract or repulse your favourite cell of the immune system?

Mast cells are attracted to chemokines that are chemoattractants. They move towards

chemokines CCL2, CCL5 and when exposed to antigen display enhanced migration towards

chemokines CXCL4 and CCL3.15

Q7-4: What chemokine receptors are expressed by your favourite cell of the immune

system?

Mast cells express of different tissue origin are able to express up to 9 different

chemokine receptors, CXCR1, CXCR2, CXCR3, CXCR4, CX3CR1, CCR1, CCR3, CCR4 and

CCR5. Mast cells have unique arrangement of CCR3, CXCR1 and CXCR2 on intracellular

cytoplasmic membranes. When mast cells become activated, CCR3 expression is upregulated on

the cell surface.16

Q8-1: Does your favourite cell of the immune system ever reside in the bone marrow?

Mast cells are made in the bone marrow and leave as undifferentiated cells. They travel

through the blood to a tissue where they will differentiate and then reside as mature mast cells.3

They do not however typically do not reside in the bone marrow as mature mast cells. When

mature mast cells do accumulate in the bone marrow it is abnormal and is usually associated with

a disease called bone marrow mastocytosis that is associated with symptoms like pruritus,

nausea, vomiting, diarrhea, and vascular instability.17

Q8-2: Does your favourite cell of the immune system ever reside in the thymus?

Yes, mast cells are normal residents of the thymus and are usually found in the connective

tissue septa. Mast cells are rare in the cortex of the thymus and also some found in the medulla

and the lobules. In people that have myasthenia gravis intralobular mast cell density of 6.5

increased to an intralobular mast cell density of 21.5 and is associated with an increase in thymic

microvessels due to mast cell secretion of angiogenic growth factors.18

Q8-3: Does your favourite cell undergo a positive or negative selection process?

Due to exhaustive literature research to date generally mast cells do not undergo a

positive or negative selection process. Generally speaking they likely would not undergo a

selection process because they do not bind antigen with TcR receptors or BcR receptors. If they

did have these receptors they might undergo a selection process to ensure their receptors do not

bind self-antigen, or bind MHC-antigen complexes too strong.19

Q9-1: Does your favourite cell of the immune system traffic to lymph nodes?

Yes mast cells do migrate to the lymph nodes. In research done by Wang et al. mice were

exposed to DNFB to induce a hypersensitivity reaction. At 24 hours 77% of mast cells de-

granulated. During DNFB sensitization the density of mast cells in the skin by approximately

50%, and mast cell density in the draining lymph nodes. To see if these mast cells were migrating

to the lymph nodes the researchers then fluorescently labelled mast cells then injected them into

the skin of the mice. Next the researchers subjected these mice to DNFB sensitization and found

that the fluorescently labelled mast cells migrated from the injection point to the draining lymph

node, then eventually migrating to the spleen. They believed that mast cells migrate from the site

of antigen encounter (DNFB) to the lymph nodes where they recruit T lymphocytes.20

Q9-2: Does your favourite cell interact with MALT?

Mast cells are part of the make up of MALT. During chronic inflammation the (mucosal)

gut associated lymphoid tissue undergoes mast cell hyperplasia. The accumulation of

extraordinary numbers of mast cells in the lamina propria and epithelium of the intestinal GALT

play a critical role in protective immunity against microbes and pathogens.21

Q10-1: Find an intravital microscopy video of your favourite cell of the immune system.

Describe the model system and what your cell is doing in that tissue.

Unfortunately I was unable to find a video the only one that I could find required paid

access. In a documented study without with the model system requires intravital microscopy of a

hamster cheek pouch for studies of microvascular dynamics of mast cell degranulation (histamine

release) when mast cells are activated. They introduced antigen to the hamster’s cheek to cause

an inflammatory reaction. In the model the mast cell degranulates and causes an influx of

leukocytes.22

Q11-1: Find an example of a pathogen immune evasion strategy against a PRR signalling

cascade. Describe in a short paragraph the significance of this host-pathogen interaction.

Host cell RNA fragments are not detected by RLRs because they are usually capped.

Some RNA viruses mimic these host cell structures as an immune evasion mechanism. They can

acquire their capped structures using host cell mRNA processing, can steal cap structure from

host mRNA fragments (e.g. influenza A virus), or they can encode their own capping enzymes

(e.g. poxviridae). With the viral genome capped and unrecognizable by the RLRs, RIG-I and

MDA5 cannot activate their downstream signalling molecules that activate IRF3, IRF7 and

NFκB. Thus, avoiding activation of Type 1 Interferon antiviral pathway.23

Q11-2: Find an example of a pathogen immune evasion strategy against a pathogen

restriction factor. Describe in a short paragraph the significance of this host-pathogen

interaction.

HIV-1 encodes viral infectivity protein (Vif) protein. HIV Vif-Cul5 E3 ubiquitin ligase

complex forms and induces the polyubiquitination of APOBEC3G. The ubiquitin tags the

APOBEC3G for proteosomal degradation. By inducing the degradation of APOBEC3G HIV-1

avoids their antiviral mechanisms such as inhibiting reverse transcription. They do this by

inducing mutations into newly synthesized negative strand DNA’s. This can prevent the

transcription of the plus strand viral genome and can even target the viral DNA for degradation.

APOBEC3G also inhibits reverse transcription by inhibiting reverse transcription DNA

elongation, as well as reverse transcription strand switching capabilities. Since HIVs Vif protein

thus allows HIV virions to be packaged without host cell APOBEC3G aboard and allowing the

virus to go forth and infect other cells successfully.24

Q12-1: Describe the type I IFN-driven anti-viral state within your favourite cell.

Interferon α and β has been shown to inhibit histamine release by mast cells in a dose

dependent manner.25 Human nasal mucosal mast cells secrete TNF-α that activates neighbouring

mast cell histamine release. IFN-α is able to inhibit mast cells release of TNF-α and thus inhibits

histamine release.26 Furthermore another study suggests that mast cells respond to IFN-α with a

decrease in TNF-α production but an increase in IL-10 and TGF-β production. Additionally the

study showed IFN-α down regulated the expression of the OX40 ligand on the mast cell surface

that is necessary for mast cell-T cell interactions therefore lowering levels of proliferating CD4+

T cells. Overall, it appears as if Type I IFNs suppress mast cell anti-viral defenses.27

Q12-2: How does your favourite cell contribute towards inflammatory processes?

Mast cells release an abundance of molecules that contribute towards inflammation. Mast

cells release protease, generating histamine-releasing peptides that contribute to inflammation.

They release tryptase that causes tissue damage, activation of PAR, inflammation and pain. They

also release corticotrophin-releasing hormone (CRH) peptides that contribute to inflammation

and vasodilation. Mast cells also releases an abundance of pro-inflammatory cytokines (IL-

1,2,3,4,5,6,9,10,13,16), INFs and TNFs (TNFα) that that cause inflammation, leukocyte

migration, proliferation and activation. Mast cells are so good at causing inflammation that they

sometimes cause inflammatory associated diseases such as asthma, atopic dermatitis,

fibromyalgia and many others. Mast cells also degranulate releasing histamine and heparin that

contributes to inflammation by promoting vasodilation, angiogenesis and mitogenesis.28

Q12-3: How is your favourite cell implicated in the resolution of inflammation and tissue

repair?

Mast cells are able to release somatostatin and chondroitin sulphate that both act as anti-

inflammatories. Mast cells also produce many cytokines/chemokines that acts as chemo

attractants for innate and adaptive immune cells that resolves the pathogen invading the tissue,

and promotes tissue repair. They release CCL1 that recruits T cells that can recognize antigen,

and then return to the lymph node to activate B cells that make antibodies against the pathogen in

order to clear it from the tissues. Mast cells also release CCL12 that attracts fibrocytes,

monocytes, eosinophils and lymphocytes, CCL20 that attracts dendritic cells, and TNF-α that

recruits neutrophils. All of these cells are able to combat the pathogen, resolving/clearing the site

of infection. Mast cells release CXCL8 that activates endothelial tissues to start angiogenesis (the

development of blood vessels) repairing vasculature in damaged tissues. Mast cells can also

release TGF-β (facilitates tissue repair by inhibits epithelial cell proliferation and increases rate

of angiogenesis) and IFN-α (increases, cytotoxicity, macrophage development and maturation,

dendritic cell activation, maturation, upregulated IFN-γ secretion).28

Q13-1: Describe how your favourite cell interacts with NK cells.

Bone marrow derived mast cells can become activated by bacterial lipopolysaccharide

(LPS). Activated mast cells induce natural killer (NK) cells to secrete IFN-γ. LPS activated mast

cells induce an NK cell IFN-γ response that is 20 fold greater than NK cell IFN-γ response

without LPS activated mast cells. It is postulated that mast cells induce the NK IFN response via

mast cells OX40 ligand binding to NK cells OX40 receptor. Researchers confirmed their findings

by blocking the OX40 ligand on mast cells, thus causing decreased IFN-γ secretion by NK

cells.29

Q13-2: What are the cytotoxic modalities in common between NK cells, NKT cells and

CD8+ T cells? Make a table with 6 comparative characteristics.

Table 1. Comparison of cytotoxic modalities between NK cells, NKT cells and CD8+ T cells.30

Comparative

Characteristics

NK cells 30 NKT cells 30 CD8+ T cells 30

Response Time Responds immediately to

antigen stimulation.

Responds immediately

to antigen stimulation.

Responds within ~7

days to antigen

stimulation (time it

takes precursors to

form functional CTLs).

Main

secretions

Perforins and granzymes,

IFN-γ,IL-6, TNF-α, Type

I and Type II IFNs and

FasL.

IFN-γ, IL-4, GMCSF,

IL-2, TNF.

Perforins and

granzymes, IFN-γ,

TNF, FasL.

Activation

Receptors

Recognizes loss of MHC

molecules on antigen

presenting cells. Can

bind directly to viral and

tumour antigens. (MHC

presence inhibits NK

activation). Activating

and inhibitory receptors

combine signals that

activate and inactivate

NK cells.

T-cell receptor that

does not recognize

MHC-antigen

complexes rather it

recognizes glycolipids

presented by the CD1d

molecule

T-cell receptor binding

to class I MHC-antigen

complex on antigen

presenting cell leads to

activation of CD8+ T

cells

Killing

Mechanism

Release of cytotoxic

granules and FasL-Fas

interactions triggering

apoptosis.

Mainly through FasL

interactions that trigger

apoptosis; indirect

activation of NK cells.

Release of cytotoxic

granules and FasL-Fas

interactions triggering

apoptosis.

Functions of

cytokines

IFN-γ promotes

macrophage

IFN-γ promotes

macrophage

IFN-γ promotes

macrophage

released. phagocytosis and

increases in class II

MHC expression, class

switching to IgG type

antibodies. IL-6 regulates

B and T cell functions

and induces

inflammation. TNF-α

mediates inflammation,

differentiation of many

cell types, cytotoxicity.

phagocytosis and




antibodies. IL-4

promotes Th2 cell

types, B cell growth

and differentiation and

class switching to IgE

antibodies. IL-2

activates NK cells and

promotes proliferation

and differentiation of T

and B cells.

phagocytosis and




antibodies. TNF

promotes inflammation,

growth and

differentiation of many

cell types.

Memory

Capacity

Yes. Express a receptor

that binds viral peptides

and transfer memory of

this antigen to naïve

animals.

No. Not capable of

forming memory NKT

cells.

Yes. Form memory

CD8+ cytotoxic T cells.

Q14-1: Describe how your favourite cell interacts with co-stimulatory molecules on DCs.

Overall, to date mast cells are not known to directly interact with co-stimulatory

molecules on dendritic cells. Mast cells are however able to bind to other receptors on dendritic

cells that leads to the up regulation of certain co-stimulatory molecules on the dendritic cell

surface. During the sensitization phase of contact hypersensitivity response bone marrow derived

mast cell use ICAM-1 adhesion interact with LFA-1 on bone marrow derived dendritic cells. This

interaction causes the up regulation of CD40, CD80, CD86, and CCR7 that in turn promote

dendritic cell maturation and migration.31

Q14-2: Compare the antigen presentation capacity between DCs, monocytes and B cells.

Make a table with 6 comparative characteristics.

Table 2. Comparison of antigen presentation capacity between dendritic cells, monocytes

(macrophages) and B cells.32

Comparative

Characteristics

Dendritic Cells 32 Monocytes 32 B Cells 32

Mechanism of

Antigen Uptake

Endocytosis and

Phagocytosis

Phagocytosis only B cell receptor-

mediated endocytosis.

Activation PRR recognition of

PAMPS, DAMPS,

cytokines.

PRR recognition of

PAMPS, DAMPS,

and cytokines. T cell

secretion of IFN- γ

B cell receptor

binding to antigen.

MHC expression Expresses both MHC

I and MHC II

Expresses both MHC

I and MHC II

Expresses both MHC

I and MHC II

Costimulatory

Molecules

CD80/86 CD80/86 CD80/86

Location of Non-

Activated Cells

Blood, Circulatory

System, Peripheral

Blood, Circulatory

System, Peripheral

Circulation, Lymph

nodes and Spleen,

Tissue Tissue Follicles

Location of Cell

When Activated

Migrates to T cell

Zone of

Subcapsular cortex of

lymph nodes,

marginal zone of

spleen and peripheral

tissues.

B cell zone- T cell

zone interface,

germinal centers, and

marginal zones of

Secondary Lymphoid

Organs (lymph nodes,

spleen).

Q15-1: Describe the complement of MHC I molecules on your favourite cell.

Mast cells major function is not antigen presentation therefore it does not have a vast

array of either MHC I or MHC II molecules. However, mast cells abnormally express HLA-G

class I MHC molecules in areas of liver fibrosis caused by hepatitis C virus.33

Q15-2: What is an MHC I tetramer? Explain how this technology could be used to

evaluate the frequency of cells responding to a specific antigen presented in MHC I

molecules.

Historically scientists have tried to directly measure CD8+ T cell responses using

antigenic peptides and MHC I. Unfortunately they had problems, as there was low affinity

between MHC/antigen complex and the CD8+ T cell receptors. This results in the

underestimation of CTLs that respond to certain antigens. A MHC I tetramer is a probe of

multiple copies of merged MHC/antigen complexes. This solves the problem of affinity as

affinity for CTLs higher and thus detects a response rate that is up to 500 times greater than past

methods.34

Q16-1: Does your favourite cell expression or interact with MHC II molecules?

‘Resting’ mast cells normally do not express MHC class II molecules. However, in tissues

that are infected or when mast cells are exposed to (TNF), IFN-γ or bacterial LPS mast cells have

been shown to have up regulated amounts of MHC class II expression on their surface.6

Q16-2: Give an example of an infection or disease in which MHC II alleles of the affected

individuals may affect the clinical outcome.

HLA MHC II alleles affect the clinical outcome of patients that are diseased with

ulcerative colitis. HLA DRB1*0103 was thought to be associated with severe cases of ulcerative

colitis. Researchers tested the hypothesis using DRB1 and DRQ1 genotyping of patients with

ulcerative colitis. They found that HLA DRB1*0103 was in 14.1% of patients they tested

compared to 3.2% of controls (individuals not infected with colitis). HLA DRB1*0103 was also

more pronounced in patients with extensive disease, it was in 25.8% of patients with mouth

ulcers, 27.2% of patients with arthritis and 35.7% of patients with uveitis. Thus DRB1*0103 is

associated with severe ulcerative colitis which usually ends with the patient requiring surgery.

Clinically, the DRB1*0103 HLA allele can then be used to predict the severity of ulcerative

colitis disease in patients as well as the likelihood that the patient will require surgery.35

Q17-1: Does your favourite cell expression or interact with TcR molecules?

Yes, studies have shown that mast cells are able to present antigenic peptide to TcR

complex on T cells. They are able to induce clonal expansion of T cells and migration of T cells

to the lymph nodes to induce an immune response.6

Q17-2: Give an example of an infection or disease in which γδ T cells play a larger role in

altering the clinical outcome than αβ T cells.

Chikungunya virus is an alpha virus that causes polyarthralgia (swelling/joint pain) in

human infections. γδ T cells play a larger role in altering the clinical outcome of this disease

compared to αβ T cells. During CHIKV infection γδ T cells are increased in number and offer a

protective role against the virus. When γδ T cell genes are knocked out in mice, leaving only to

αβ T cells as a defense, there is more intensified inflammation in the mouse foot and ankle joints.

Therefore T cells were shown to protect the host by reducing the amount of viral induced

inflammation, tissue and joint damage.36

Q18-1: What type of proteome is active in your favourite immune cell?

Mast cell have a proteome that is involved in activation of mast cell degranulation to

induce a proinflammatory response to encountered antigens. The mast cell genome carries genes

for many proteins involved in the signalling pathways such as SYK, LYN, MAPK, and others.12

Q18-2: Give an example of an infection or disease in which the expression levels of CD5+ on

T cells correlated with the immune outcome.

In tumours that can be cancerous or viral caused CD5 expression levels control the

activation of some T cells and thus their susceptibility to cell death. Researchers were able to

show that T cell death was inversely proportional to the expression of CD5+ on T cells. When

CD5+ was neutralized with an antibody there was an increase in tumour mediated T lymphocyte

cell death. Thus as CD5 increases T cell lysis decreases and CD8+ survival is promoted and thus

defense against the tumour is promoted.37

Q19-1: What signals are active in your favourite immune cell?

The main signal that is active in activated mast cells are the signalling pathways that are

induced by stimulation of the high–affinity IgE (FcεRI) receptor. It signals through LYN and

SYK tyrosine kinases that phosphorylate LAT adapter molecule. This leads to down stream

signaling activating MAPK and ERK that activate transcription factors (NFAT, NFκB, API) that

promotes to cytokine production. LAT also activates PLCγ that activates protein kinase C (PKC)

through down stream signaling molecules (DAG). PKC promotes the increase of free cytosolic

calcium, which is an essential signal for mast cell degranulation. cKit stimulation causes

recruitment and activation of SRC kinases, PLCγ and P13K, and JAK-STAT molecules. JAK-

STAT pathway and MAPK pathway promotes mast cell growth, differentiation, survival,

chemotaxis and cytokine production.12

Q19-2: Give an example of how effector T cells affect the function or survival of your

favourite immune cell.

Th1 and Th2 are effector T cells that secrete cytokines that have chemotactic activity for

mast cells. Th2 cells can secrete interleukin-4 (IL-4) and IL-8 that are mast cell chemo

attractants. Th1 cell secrete TNF-α that is also a mast cell chemoattractants. Thus, Th1 mediated

inflammation (TNF-α release) and Th2 mediated inflammation (IL-4 and IL-8 release) recruits

mast cells to the site of inflammation. This migration completely changes the mast cells function,

at the site of inflammation the mast cell is likely to encounter antigen, thus causing the mast cell

to degranulate contributing to further inflammation.38

Q19-3: Give an example of how memory T cells affect the function or survival of your

favourite immune cell.

Due to exhaustive literature search, one may conclude that there is limited studies about

how memory T cells affect the function or survival of mast cells. However, there is data about

how mast cells affect the function of CD4+ memory T cells. Mast cells are able to form an

immunologic synapse with memory CD4+ T cells. Mast cells secrete IL-22 and TNF-α that

promote the differentiation of memory CD4+ T cells into the Th22 T cell phenotype.39

Q20-1: Does your favourite cell secrete or binding antibodies?

Generally mast cells do not secrete antibodies however they do bind antibodies. IgE

molecules have a tail region that has a high affinity for Fc receptors (FcεRI) on the surface of

mast cells. IgE antibodies then bind the Fc receptor on the mast cell. This bound complex mast

cell surface receptors for antigen detection. When antigen does bind to the IgE antibodies that are

bound to the mast cell surface this promotes mast cell degranulation and cytokine secretion.40

Q20-2: Can your favourite cell modulate isotype switching in B cells? Why or why not?

Mast cells secrete IL-6, IL-5, TGF, and other cytokines and express the CD40 ligand that

can interact with B cell CD40 receptor. When B cells were co cultured with mast cells they were

able to interact and B cells showed and increased expression of IgA. The increase expression of

IgA suggests that B cells were modulated by mast cells to isotype switch to IgA.41

Q21-1: Does your favourite cell participate in B cell somatic hypermutation or class-switch

recombination? If so, how?

Due to exhaustive literature search it can be concluded that no, mast cells do not directly

participate in B cell somatic hypermutation. However, generally speaking they may play an

indirect role. Mast cells have been shown to have upregulated expression of MHC class II in the

presence of LPS, TNF, or IFN-γ.6 These mast cells can present antigen on MHC class II

molecules to naïve T cells that become activated and move to T cell zones in the lymph nodes.

Here B cells make contact with antigen specific T cells that can last for many hours activating the

B cells down regulating CCR7 and maintaining CXCR5 levels that promote B cell chemotaxis to

the follicular region where the B cells form germinal centers. Here the B cells undergo somatic

hypermutation that provides antibody diversification. 42

Q21-2: Does your favourite cell interact with B-1 cells?

Mast cells usually do not interact directly with B-1 cells. Although studies have shown

that mast cells indirectly play a role in B-1 B cell proliferation. IL-33 promotes B-1 cell

proliferation but depends on IL-5 that is largely mast cell dependent. When mast cells were

deficient, IL-33 activation of B-1 cells was also reduced.43

Q22-1: Does your favourite cell participate in antibody- dependent effector immune

responses? If so, how?

Yes. Mast cells participate in an antibody-dependent degranulatory synapse. Mast cells

express IgE and IgG antibodies on the surface that act as receptors for certain antigens. When

mast cells bind antigen on their antibodies they are triggered to begin their effector response.

Their effector immune response involves degranulation and release of inflammatory molecules

such as histamine, chymases, tryptases, and many cytokines that draw other cells to the site of

antigen encounter.

In study done they found that mast cell FcR stimulation by (IgE/IgG) antibody cell bound

antigen results in a degranulatory synapse formation that allows direct delivery of secretory

granules to the mast cells target cell.44

Q22-2: Does your favourite cell participate in cytotoxic killing of target cells? If so, how?

Mast cells indirectly participate in cytotoxic killing of target cells. Mast cells are able to

internalize some bacteria (enterobacteria) through phagocytosis. They process the pathogen and

then present the antigen on MHC class I molecules to T cell receptors on CD8+ cytotoxic T cells.

Mast cells also produce IL-4. Mast cell antigen presentation and IL-4 secretion leads to the

activation, proliferation and differentiation of CTLs. IL-4 can also enhance the cytotoxic killing

of antigen of CTLs. Therefore, mast cells can indirectly participate in the cytotoxic killing of

some bacteria.45

Q23-1: Does your favourite cell participate in atopic disease?

Asthma, allergic rhinitis, and atopic dermatitis are all atopic diseases of childhood that are

all mediated by IgE.46 Mast cells participate in atopic disease as they play a large role in asthma.

When asthmatics inhale allergens, mast cells equipped with a particular IgE antibody binds to the

allergen.47 These mast cells are found in the airway smooth muscle bundles and when activated

release histamine, prostaglandin D2, cysteinyl leukotrienes that cause airway smooth muscle

spasms. Mast cells also release serine protease tryptases that can cause bronchoconstriction,

airway remodeling, and airway hyper-responsiveness through a variety of mechanisms.48

Q23-2: Does your favourite cell interact with epithelial cells? If so, how?

Yes during asthma mast cells migrate to the airway epithelial cells. Here mast cells

infiltrate bronchial epithelium where they sit at the place of entry for any inhaled antigenic

allergens. If they encounter antigen they may play a part in antigen presentation and T cell

proliferation and differentiation responses. They may also adhere directly to the epithelium and

secrete tryptases that promote epithelial production of IL-8 release that promotes neutrophil

infiltration and inflammatory responses.49

Q24-1: Does your favourite cell interact with T regulatory cells? If so, how?

Mast cell interacts with T regulatory cells through and OX40 receptor-ligand interaction.

This interaction shows that T regulatory cells can inhibit FcεRI-dependent mast cell

degranulation.50 Activated mast cells have been shown to be able to counteract T regulatory cell

inhibition of degranulation through engagement of OX40 receptor and ligand and the production

of IL-6 and Th1 and Th2 cytokines that promote T regulatory cell differentiation into Th17 T cell

phenotype.51

Q24-2: Does your favourite cell participate in autoimmune disease?

Yes. Mast cells participate in autoimmune rheumatoid arthritis. Mice that were deficient

in mast cells were found to have much less joint inflammation. Mast cells secrete many

proinflammatory cytokines (TNF, IL-1β, IL-17, and tryptases). Tryptase works with heparin to

promote neutrophil infiltration and activates synovial fibroblasts that degrade cartilage and bone

through interaction with PAR2 receptor. Mast cells self amplify in rheumatoid arthritis by

secreting TNF-α that causes fibroblasts to produce SCF that increases mast cell recruitment to the

synovial fluid in the joint.50 When mast cells degranulate they release heparin, proteases, TNF,

IL-1, 2, 3, 4, 6, VEGF and many other cytokines into the synovial fluid histamine further increase

inflammation, neutrophil and leukocyte infiltration, fibroblast activation and additional

outcomes.52

Q25-1: Is your favourite cell impacted by a primary immunodeficiency? If so, how?

Yes, mast cells are impacted by PLAID is PLCγ2 associated antibody deficiency and

immune dysregulation a primary immunodeficiency disease. It is caused by a mutation in

phospholipase C-γ2 gene. It effects people from birth and causes abnormal allergic responses to

cold temperatures. Mast cells are impacted by abnormal activation by cold temperatures that

leads to their degranulation.53

Q25-2: Is your favourite cell impacted by a secondary immunodeficiency? If so, how?

Yes. Patients that have AIDS, an acquired secondary immunodeficiency showed

decreased mast cell reactivity to antigen. Researchers believe that AIDS is associated with

decrease in local mast cell density and releasibility. It is hypothesized that the decrease in mast

cell density is related to HIV-related hematopoietic dysfunction that causes decreased

proliferation of mast cells. Another hypothesis is that HIV may directly inhibit mast cell

degranulation through binding in ways similar to the ways in which HIV gp120 depresses β-

adrenergic responsiveness of astrocytes and microglia.54

Q26-1: With a partner from BIOL4931, pick a human infection or disease that involves

both your cell types. Explain how together your favourite cells cooperate to ensure an

effective immune response. You must present information comparing and contrasting how

your cells are involved in innate immune signalling, antigen presentation and effector

responses. 300 word minimum.

Atopic dermatitis, also called eczema, causes itchy skin that is red, warm, and tender and

it usually runs in the family. Researchers are still trying to figure out what exactly causes atopic

dermatitis.55 Many inflammatory diseases such as atopic dermatitis involve mast cells in cross-

talk with T cells.56 Studies have shown that mast cell and T cell interaction can promote the

activation of mast cell transcriptional activity.55 When mast cells bind to activate T cells in atopic

dermatitis mast cell effector response is promoted which is defined as mast cell degranulation,

proinflammatory cytokine production, and TNF-α production.56 T cells play a large role part in

effector response in atopic dermatitis. In atopic dermatitis there are several effector T cell

subtypes such as Th9, Th17, Th22 cells (that are differentiated CD4+ T cells) that express high

levels of IL-9, IL-17, IL-22.56 T regulatory cells as well as mast cells are also present and secrete

IL-10 that is an immunomodulatory cytokine that functions to inhibit skin inflammatory

processes in atopic dermatitis.57,58 Th9 cell are pro-inflammatory because they recruit mast cells

to the site of atopic dermatitis through the production of IL-9. Mast cells that secrete IL-13 and

IL-4 promote Th2 T cell effector responses.58Activated effector mast cells in atopic dermatitis

secrete many cytokines such as, TNF-α, TGF-β, VEGF, IFN-α/β/γ, IL- (1-6,8-16, 18 and 25). In

atopic dermatitis mast cells can function as antigen presenters, where they use class II MHC

molecules to present antigen to CD4+ T cells. T cells do not present antigen. T-cells and mast

cells may also interact through OX40-OX40L interactions triggering T cell proliferation in atopic

dermatitis.59 Overall, mast cells promote the pathogenic inflammatory response of atopic

dermatitis while CD4+ T helper cell subtypes regulate the function of mast cells to ensure they

are not overly pathogenic to the host.

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