Naïve T cells effector T cells

Target cells

APC

effector T cells

Ag

1. Survival signals: re-enforce the positive selection

by MHC: self peptide

2. Ensure the high probability of encountering pathogens, Only one in 104-106 is to be specific for particular Ag

Naïve T cells circulate from bloodstream through lymphoid organs and back to bloodstream, making contact with many thousand APC in lymphoid tissue:

Naive T cells encounter antigen during their Recirculation through peripheral lymphoid organs

Activation of naïve T cells required three signals delivered from APC

CD28-B7 induce T cells express growth factor IL-2 and its high affinity receptor (CD25, IL2R)

2. The production of armed effector T cells

3. General properties of armed effctor T ells.

4. T ell mediated cytotoxicity

5. Macrophage activation by armed CD4 Th1 cells

T cell activation and Cell Mediated Effector Response

1.Entry of naïve T cells and APC cells into peripheral Lymphoid organs

1. Lymphocytes entyry into lymphoid tissues

3. Antigen presentation cells

-------Adhesion molecules

Entry of naïve T cells and APC cells into peripheral Lymphoid organs

-------Chemokines

Distinct stages for lymphocytes entry into lymph node require the activity of adhesion and chemokines

CCL21:CCR7 (T cells) CXCL12:CXCR4 (Tcells)

Lymphocyte migration, activation, and effector function depend on cell-cell interaction mediated by cell

adhesion molecules

Adhesion molecules:1.Selectin, integrin, members of Ig superfamily, mucin like molecules2.Broad role in generation of lymphocyte response3.migration, effector T cells-target cells, getting lymphocyte together; B-T cell interaction

Selectin: lymphocyte homing to particular tissue leukocyte: L selectin (blood to lymph tissue), vascular endothelium : P-or E- selectin (blood to infection sites)

Cell surface sugar group : Vascular addressins: CD34, GlyCAM-1

Sulfated Sialyl-LewisX

L-Selectin and mucin like vascular addressins

Integrins are important in T-lymphocyte adhesion

, subfamily (large , common ), 2, leukocyte integrins, all T cells, known as LFA -1(lymphocyte function associated antigen-1) , most important one, naïve and effector T cell migration1, leukocyte integrins, late stage in T cell activation, very late activation antigen (VLA), armed effector T cell to infection sites

Integrins are important in T-lymphocyte adhesion

Integrins: (development, inflammatory response)

1.cell-cell, cell-extracellular matrix; signals induce intergrin bind to their ligand tightly:

a. chemokine enhance integrin binding to its ligand ex: CCL21 (SLC; secondary lymphoid tissue chemokines) expressed by DC, stromal cells, high vascular endothelium cells, bind to CCR7, (naïve T cell to lymphoid tissue)

b. T cell receptor trigger T cell integrin-ligand tightly

Ig domain Adhesion molecules involved in leukocyte interactions

Ig domain superfamily:

CD4, CD8, CD19, intercellular adhesion molecules (ICAM)

ICAM-1.2.3 ICAM1,2: endothelium cells, lymphocytes, ICAM3: naive T cells

LFA: lymphocyte function association antigen

Lymphocytes in the blood enter lymphoid tissue by crossing the walls of high endothelium venules

CCL21

血球滲出

CCL21CCL18

CCR7

1. Lymphocytes entry into lymphoid tissues

2. Antigen presentation cells

-------Adhesion molecules

Entry of naïve T cells and APC cells into peripheral Lymphoid organs

-------Chemokines

Antigen presenting cells

Dendritic cells vs Macrophage vs B cells

Selectivity of antigen uptakeAntigen process prosperities, costimulatory molecules, Migration behavior

Distinct function of APC in initiating T cell response

Antigen-presenting cells are distributed differentially in the lymph node

Dendrtic cells: T cell area a wide variety pathogensMacrophage: Marginal sinus, (lymph afferent), medullary cord (Lymph efferent) T cell areas ingested pathogens

B cells: lymphoid follicles soluble antigens (toxin)

B cells as APC require:1. Appropriate receptor (internalize)2. Antigen at high density

Two different functional classes of dendritic cells

cDC pDC

cDC: CD11c+: activation of naive T cells

pDC: sentinels 哨兵 primarily for virus infection and produce a lot of IFN and less efficiency in priming naïve T cells, TLR7 and TLR9 for sensing virus infection

Dendritic cells process pathogens via different routes

DC are susceptible to infection by quite a number of viruses

Dendritic cells mature through at least two definable stages to become potent antigen-presenting cells

in lymphoid tissue

1. The ability to activate T cells Lymphoid>>>epithelial and solid organs

2. Immature dendritic cells: Low MHC, No B7 phogocytosis: using DEC250 receptor Macropinocytosis (non-specific) Induce tolerance to self antigen

3. Mature dendritic cells: High level: MHC, adhesion adhesion molecules, DC-SIGN, chemokine (DC-CK CCL18, attract naïve T cells),CCR7 (chemokine receptor, homing to lymphoid org.), IL-12

Dendritic cells mature through at least two definable stages to become potent antigen-presenting cells

in lymphoid tissue

Inflammatory response: ----transport antigen to the local lymphoid tissue---- Enable APC to present antigen effectively to naïve T cells.

Microbial substances can induce co-stimulatory activity in macrophages

Kupper cells and Macrophage in spleen :little MHC II and No TLR

Resting macrophage:Little or no MHCIINO B7

Insoluble antigen

Macrophage are scanvenger cells that can be induced by pathogens to present foreign antigens to naïve T cells

Adjuvant

B cells can use their immunoglobulin receptor to enhance the presentation of specific antigen very efficiently to T cells

B cells are highly efficient at presenting antigen that bind to their surface immunoglobulin

B cells: soluble antigen, constitutively high levels of MHC II, induced B 7.2 by microbial Protein

How important of B cells as APCs? vs Dendritic cellsSoluble antigens are not abundant during natural infection

Summary of APC

The properties of the various antigen-presenting cells

2. The production of armed effector T cells (Priming)

3. General properties of armed effector T ells.

4. T ell mediated cytotoxicity

5. Macrophage activation by armed CD4 Th1 cells

T cell activation and Cell Mediated Effector Response

1.Entry of naïve T cells and APC cells into peripheral Lymphoid organs

Cell-surface molecules of the Ig superfamily are important in the interactions of lymphocytes with

antigen-presenting cells

DC-sign: lectin only dendritic cells

CD58: also known as LFA-3

The initial interaction of T cells with APC is mediated by cell-adhesion molecules

ICAM3: LFA1 and DC-Sign

Synergize

redundancy

Transient adhesive interactions between T cells and antigen-presenting cells are stabilized by specific antigen recognition

The initial interaction of T cells with antigen-presenting cells is mediated by cell adhesion molecules

TCR+MHC-peptide: Increase the affinity of ICAM1 and LFA1The association lasts for several days , during which time naïve T cell proliferates and its progeny associate with APC: proliferation and differentiation to armed T cells

Activation of naïve T cells required three signals delivered from APC

CD28-B7 induce T cells express growth factor IL-2 and its high affinity receptor (CD25, IL2R)

The principal co-stimulatory molecules expressed on antigen-presenting cells are B7 molecules, which bind the T-cell protein CD28

Co-stimulatory molecules

B7 moleculesB7.1 (CD80) and B7,2 (CD86)Ig superfamily

CD28: ligand of B7

CD28-B7 +TCR-Self/MHC

CD40L (T cell surface)

CD40L-CD40 (APC)

B7 (APC) Another costimulation molecules: T cells: 4-1BB (CD137)APC: 4-1BBL

IL-2 and IL-2R increase

High-affinity IL-2 receptors are three-chain structures that are produced only on activated T cells

Activated T cells synthesize the T cell growth factor interleukin-2 and its receptor

CD25: chain

Resting T cells: , moderate affinity high IL-2Activated T cells: High affinity Low IL-2

IL-2 are necessary for the T cell proliferation

Anergic cells can not produce IL-2

Activated T cells secreted and response to IL-2

T-cell activation leads to the increased expression of CTLA-4, an inhibitory receptor for B7 molecules

CTLA-/-: proliferative massively, Lymphadenopathy, is important in lymphocyte homeostasis

CD28: rest and activated T cells

CTLA-4 (CD152)--CD28 related protein also bind to B7--Expressed on activated T cells. --less than CD28 even in high peak, --In terms of the B7 avidity, CTLA is 20X higher than CD28

B7-CD28: positive signalsB7-CTLA4: inhibitory signals

The requirement for one cell to deliver both the antigen-specific signal and the co-stimulatory signal is crucial in preventing immune responses to self antigens

T cell anergy

MHC class I present endogenous peptide whichis not eliminated in the thymus

Why the retention of angeric T cells?

Anergic cells can not produce IL-2

Armed effectors T cells can respond to their target cells without co- stimulation

Armed effector T cells changes the expression of several cell-surface molecules

Armed effector : Loss of L-selectin results in ceasing to recirculate through lymph node Expression of VLA-4 allow the activated cells to bind to VCAM which is expressed at the sites of inflammation

CD45RO: associate with TCR and CD4, more sensitive to peptide/MHC

1.Naive CD8 T cells can be activated directly by potent antigen-presenting cells

Naïve CD8 T cells can be activated in different ways to become armed effector cells

Need more co-stimulatory molecules than ThTc against Tumor

Some CD8 T-cell responses require CD4 T cells

CD40-CD40L:Increase the co-stimulatory molecules on APC

4-1BBL:another co-stimulatory molecules only expressed on activated DC, macrophage and B cells

Activated CD40 increase the co-stimulatory molecules expressed on APC

2. Naïve CD8 T cells can be activated in the presence of Th. In these response CD8 and CD4 T cells must recognize related antigens on the surface of the same antigen presentation cells

Various signal3 causes naïve CD4 T cells to acquire distinct effector function

Nature T reg: CD4+CD25+, 10-15% Inhibit T cell proliferation, IL10 and TGF

Th3: Mucosa, IL-4, IL-10 and TGF Tr1: culture in IL-10, TGFAdaptive regulatory: TGFinducted Foxp3, TGF

IL23

The different type of effector cells are specialized to deal with different types of pathogens

Effectors Action depend on:The array of membrane, secreted protein, and mediator released upon receptor ligation

The effector proteins focus on the target cell by mechanism that activated by recognition of antigen on the target cells

Chemokines

Prevent autoimmunity

proinflammatory

2. The production of armed effector T cells

3. General properties of armed effctor T ells.

4. T ell mediated cytotoxicity

5. Macrophage activation by armed CD4 Th1 cells

T cell activation and Cell Mediated Effector Response

1.Entry of naïve T cells and APC cells into peripheral Lymphoid organs

Interactions of T cells with their targets initially involve nonspecific adhesion molecules

TCR+MHC-peptide;prolong the binding of target cells with effector cells

Th bind to macrophage or B cells for long period

? Disengage from target cells.

Tight junctions are formed between armed effector T cells and their targets

SMAC: supramolecular adhesion complex

The area of contact between an armed effector T cells and its contact forms an immunological synapse

a B cell: a T cellpSMAC cSMAC

Control the delivery of effectors:1.Stable binding, tight held, narrow space2.Focus the delivery at the site of contact 3. Triggers the synthesis or release

The polarization of T cells during specific antigen recognition allows effector molecules to be focused

on the antigen-bearing target cell

Nonspecific adhesion binding

TCR binding to target cells

T cell become polarized : aligns the microtubule organization center (MTOC), sectory aparatus, Golgi

Binding of the T-cell receptor complex direct release of effector molecules and focus them on the target cells

The different types of effector T cells produce distinct sets of effector molecules

Fas ligand (FasL): Membrane associated TNF-related moleculesexpressed by cytotoxic T cells and some Th cells,which kill the activated Fas bearing lymphocytes

The effector functions of T cells are determined by the array of effector molecules that they produce

The nomenclature and functions of well-define T-cell cytokines I

Most of the cytokines have local effects that syngergize with those of the membrane bound effector molecules

Synthesis of IL-2,IL-4 and IFN- is controlled and confined to target cells

More distant effect:IL-13 and GM-CSF producing macrophage and granulocytes

IL-5: eosinpophilIL-3 and GM-CSF: DC

The nomenclature and functions of well-defined T-cell cytokines II

The nomenclature and functions of well-defined T-cell cytokines III

Cytokine-mediated generation and cross regulation of Th subsets

Cytokine receptors belong to families of receptor proteins, each with a distinctive structure

Cytokines and their receptors can be grouped into a small number of structural families

I:: ligand specificity or : signal transduction

TNF receptor: ligand: trimer, membrae bound

Cytokines: Hematopoietin IFNTNF

2. The production of armed effector T cells

3. General properties of armed effctor T ells.

4. T ell mediated cytotoxicity

5. Macrophage activation by armed CD4 Th1 cells

T cell activation and Cell Mediated Effector Response

1.Entry of naïve T cells and APC cells into peripheral Lymphoid organs

Cytotoxic CD8 T cells can induce apoptosis in target cells

Why cell mediated cytotoxicity ? Intracellular pathogen:Not accessible to AbEliminated by destruction or modification of infected cells

Tc+target cells:Program to death within 5 minutesDeath take hours to be evident ???

Apoptosis:Kill host cell , cytosolic pathogens Nonviral cytosolic pathWhy is apoptosis but not necrosis ????

Cytotoxic effector proteins released by cytotoxic T cells

Ca2+ dependent release of specialized lytic granule

Perforin: pore

Granzymes:Three digestive enzymeSerine protease (as trypsin and chymotrypsin)

Granulysin :Apoptosis and antimicrobial

CTL-mediated pore formation in target-cell membrane

Perforin+ phosphorylcholine Polymerize pore+Ca2+

G:granules, N: nucleus, M: mitochondrion, Go: Golgi.

Perforin released from the lytic granules of cytotoxic T cells can insert into the target cell membrane to form pores

Capase 3

Capase-activated deoxyribonucleotides (CAD)

Apoptotic cells was taken up by phagocytosis and completely digested without induction of co-stimulatory protein

CAD I-CAD

CAD

TCR aggregation signal through the ITAM motif for granule release, similar to mast cells

Both Perforin and granzyme are required for the effectively cell killing

Two pathways of target-cell apoptosis stimulatedby CTLs

Granzyme B

Cytotoxic T cells kill target cells bearing specific antigen while sparing neighboring uninfected cells

1. Store the inactivated cytotoxic proteins in lytic granules

2. TCR aggregation leads to synthesis of perforin and granzyme

3. Kill the target cell one by one, one point contact at any one time

4. Tc produce IFN-inhibit viral replication)TNFTNFkill some target cells).

2. The production of armed effector T cells

3. General properties of armed effctor T ells.

4. T ell mediated cytotoxicity

5. Macrophage activation by armed CD4 Th1 cells

T cell activation and Cell Mediated Effector Response

1.Entry of naïve T cells and APC cells into peripheral Lymphoid organs

TH1 cells activate macrophages to become highly microbicidal

--Clinical important infections, microbial inhibit the fusion of phagosome and lysosome or acidification of these vesicles --Macrophage require two signals to be activated:1. IFN-and other ways sensitizing cells to IFN , such as CD40L, 2. Membrane associated TNF-, TNF- of macrophage can replace CD403. Tc produce IFN- (cooperate with little LPS) IFN-: Th1 and Tc, but not Th2

The production of cytokines and membrane-associated molecules by armed CD4 Th1 cells requires new RNA and protein synthesis

Th1 contact with target cells longer than Tc:

--In many cases the macrophage is able to destroy pathogens without the need for T cells activation

Activated macrophages undergo changes that greatly increase their antimicrobial effectiveness and amplify

the immune response IFN-: contact and focal secretionActivated MF: 1. more effectively fuse phagosome and lysosome 2. MHC II, B7, CD40 and mTNF-

4. TNF-(M) +IFN- (Th1)iNOS, NO, O2

- (destroy extracellular Pathogens)

IL-12Naïve T cells

Th1

5. Bad: Consume large energy, tissue destruction

6. regulation: IFN-: mRNA half life is short, new protein promote cytokine mRNA degradation TGF-, IL-10 (Th2), (Th2) inhibit M activation

3.

The immune response to intracellular bacteria is coordinated by activated TH1 cells

CCL2

Granulomas form when an intracellular pathogen or its constituents cannot be totally eliminated

T cells: Th1 and Th2, Th2 preventing wide spread tissue damage by regulating Th1 activatity.

Lack of oxygen and cytotoxic effect of activated macrophage cause the dead center like cheese: Caseation necrosis

Th1, nonactivation, disseminated infection, present in patients with AIDS and concomitant mycobacterial infection

Further Reading:Immunology (Kuby): 259-260, 262-265, 351-361Immunobiology(Janeway):323-372

Th1 vs Th2 ????

1. cytokines, IL-12, IFNand IL-42. Costimulatory signal3. The nature of peptide:MHC

Cell mediated (IgG) Humoral , IgM,IgA, and IgE

The stages of activation of CD4 T cells

The differentiation of CD4 T cells into Th1 or Th2 determine whether humor or cell-mediated immunity will be dominate