adaptive immunity

THE IMMUNE SYSTEM

•Defense Mechanisms

Adaptive Immunity

• Immunity that an organism develops during lifetime

• Develops after exposure to antigens• Invovles the activity of lymphocytes• Includes 3rd line of defense

Adaptive Immunity (Specific immunity)

• Specificity

• Memory

• Ability to distinguish b/w self vs non-self

• T and B cell

Types of Adaptive Immunity

1. Antibody-Mediated Immunity (AMI) or Humoral Immunity– B lymphocytes

2. Cell-Mediated Immunity (CMI) or Cellular Immunity– T lymphocytes

Note: B and T cells ……..blood, lymph, lymphoid tissues such as spleen, lymph nodes etc.

•Lymphocyte Formation

CHECKPOINT

• 1. What are the two main types of lymphocytes?

• 2. What is an antigen? Name some examples.

Cell-Mediated Immune Response

• T cells

• Immune resoponse to infected cells( viruses, bacteria and parasites (Pathogens) within cells)

• Defense against cancer and transplant cells

•Chapter 21, Immune System •8

T-Lymphocytes

• Helper T cells – secrete CYTOKINES help B cells Tc cells to divide• Cytotoxic T cells (killer T cells) Kill infected body cells• Memory T cells remain in body

How do T cells know a cell is infected?

• Infected cells digest some pathogens and MHC proteins carry pieces to cell surface

• Antigen Presenting Cell (APC)• Alerts Helper T cells

•MHC proteins displaying

foreign antigensinfectedcell

•T cell with antigen receptors

•TH cell


• MHC proteins,mark a cell as self

• The two classes of MHC proteins are:– Class I MHC proteins – found on virtually all body cells

– Class II MHC proteins – found on certain cells in the immune response

MHC Proteins

Macrophages

Antigen-Presenting Cells

– B cells– Dendritic cells– macrophages

Helper T Cells (TH)

• bind to other white blood cells that have previously encountered an antigen– stimulate proliferation of other T cells– Stimulate B cells that have already become bound

to antigen

• Without TH, there is no immune response


The central role of Helper T Cells (Boss)

•Chapter 21, Immune System •15•Figure 21.17a

Cytotoxic T Cell (Tc)

• Destroys infected body cells– binds to target cell– secretes perforin protein

• punctures cell membrane of infected cell– apoptosis


Cytotoxic T cells

•Killer T cellbinds to

infected cell

• Destroys infected body cells– binds to target cell– secretes perforin protein

• punctures cell membrane of infected cell– apoptosis

•infected cell•destroyed

•Cytotoxic T cell

•1

•Accessoryprotein

•Class I MHCmolecule

•Infectedcell

•Antigenreceptor

•Antigenfragment

•Cytotoxic T cell

•1 •2

•Accessoryprotein


•Infectedcell

•Antigenreceptor

•Antigenfragment

•Perforin

•Pore

•Gran-zymes

The killing action ofcytoxic T cells on an infected host

cell.

•Cytotoxic T cell

•3•1 •2

•Accessoryprotein


•Infectedcell

•Antigenreceptor

•Antigenfragment

•Perforin

•Pore

•Gran-zymes

•ReleasedcytotoxicT cell

•Dyinginfected cell

Figure 23.11 (1 of 2)

CMI

• Human Immunodeficiency Virus– virus infects and destroys helper T cells

• helper T cells don’t activate rest of immune system: killer T cells & B cells

• AIDS: Acquired ImmunoDeficiency Syndrome– infections by opportunistic

diseases– death usually from – “opportunistic” infections

• pneumonia, cancers

HIV & AIDS

•HIV infected T cell

ANTIBODY-MEDIATED (HUMORAL) IMMUNITY

• targets extracellular microorganisms (Bacteria and viruses circulating in the blood)

• B-lymphocytes (B cells)………. Antibodies • Antibodies… extracellular fluids and surface of B

cells

•Pathogen

•1

•Antigen-presentingcell •Antigen

fragment

•Class IIMHC

molecule

•Antigenreceptor

•Accessoryprotein

•Helper T cell

•Pathogen

•1 •2


fragment

•Class IIMHC

molecule

•Antigenreceptor

•Accessoryprotein

•Helper T cell

•B cell

•Cytokines

•Activatedhelper T cell

•Pathogen

•3•1 •2


fragment

•Class IIMHC

molecule

•Antigenreceptor

•Accessoryprotein

•Helper T cell

•B cell

•Cytokines

•Activatedhelper T cell

•Memory B cells

•Plasma cells•Secretedantibodies

Antibody-mediated (humoral) immunity = AMI

• 1- Macrophages phagocytize a pathogen and present an antigen to a matching helper-T cell

• 2- At the same time, some pathogens contact B-cells matching the pathogen’s antigens

• The helper-T cells multiply, secrete lymphokines which stimulate the B-cells to multiply and specialize into plasma cells

• The plasma cells secretes antibodies

The Nature of Antibodies

• Globular proteins called immunoglobulins• Basic antibody structure has 4 polypeptide chains

– 2 identical light chains– 2 identical heavy chains

• Regions of heavy and light chains– Variable– Constant

Antibody Molecule

•antigen binding sites

•antigen

•light chains •heavy chains

•Immunoglobin ClassesImmunoglobin Classes

• IgM• 1st response to antigen• Can’t cross placenta

• IgG• Most common form• Crosses placenta

(passive immunity to fetus)

• IgA• Secreted from mucus

membranes• In colostrum

• IgD• B cell activation• Can’t cross placenta

• IgE• Histamine

reactions and allergies (mast cells, basophils)

First and second exposures to a pathogen

Role of the antibodies

•The classical compliment pathway, resulting in lysis of a target cell

Types of Immunity

• Active ImmunityNatural active immunity - acquired due to infectionArtificial active immunity – vaccination

• Passive ImmunityNatural passive immunity• placenta to the fetus• Colostrum

Artificial passive immunity• Injection of immune serum

Types of Acquired Immunity

Immune system Disorders• Allergies• Allergies are exaggerated (hypersensitive) responses to

antigens called allergens

• Allergens…. antigens

•© 2011 Pearson Education, Inc.

•41

QUESTIONS PLEASE

adaptive immunity

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