Functions of Antibodies

Antigen binding sites are variable

• differ based on which antigen they are designed to bind

• Fab regions bind to antigens

• Fc region binds to phagocytes and activates them

5 classes of antibodies

• IgG, IgA, IgE, IgM, IgD

• IgG - most abundant in blood, activates complement sys

• IgE - associated w/ allergic reactions

• IgM - those that react to different blood antigens, activate complement system

Agglutination

Because of the two binding on each antibody, they can bind two foreign antigens each

• this allows antibodies to bind or “glue” foreign antigens into a clump, which immobilizes them so that other immune cells can engulf and destroy them

Opsonization

Enhancement of immune reaction against bacteria by antibodies or portions of the complement cascade

• bacteria coated or “tagged” with antibodies are easier for phagocytes to find and ingest

Activate other components of the immune system

• Antibodies attached to foreign antigens can trigger the release of cytotoxins from Natural Killer cells or eosinophils or cytokines from Mast cells

Antibodies can also activate complement proteins

• which can create membrane attack complexes

Antibodies attached to B-cells, when triggered by foreign antigens, cause those B-cells to become either ….

• plasma cells or memory B-cells

T lymphocytes provide cell mediated immunity

Designed to destroy pathogen-infected cells

• this is the primary way viruses are destroyed

→ remember, they must enter cells to reproduce

• Any bacteria that enter cells are also targeted

• Infected cells display foreign antigens on their MHC class I platforms

→ Killer T-cells seek out, bind to, and destroy these infected

Killer T-cells (aka cytotoxic T cell)

• Attack infected cells

→ bind to MHC class I-antigen complex

Killer T-cels destroy infected cell similarly to the Natural Killer Cells mentioned earlier

• Secrete perforins

→ form pores in infected cell’s membrane

• Secrete granzymes

→ destroy cell’s DNA

→ stimulate apoptosis

Helper T cells

Interact w/ antigen-presenting cells

→ bind to their MHC class II-antigen complexes

Helper T cells become activated

• Do not directly attack infected cells

• Bind to and stimulate B-cells to reproduce and differentiate

• Secrete cytokines to enhance immune response

→ Interferon-gamma

→ colony-stimulating factors

→ interleukins

Interferon-gamma

Activate macrophages

Colony-stimulating factors

Enhance leukocyte production

Interleukins (ex: IL-2)

• Activate killer T-cells

• Enhance mast cell and eosinophil function

• Activate plasma cells to produce antibodies

Defenses against bacteria

Defenses against viruses

1. Killer T-cells

2. B lymphocyte

3. Immunoglobulins

4. Opsonization

5. Killer T cells

6. Bradykinin