Antibodies

Structure

• 2 light chains, 2 heavy chains

• Antibodies that originate from the same plasma cell have antigen specificity identical to each other and the BCR of the activated B cell

• Fab region = antigen binding region

• Fc region = antibody stem

Functions

• neutralization of microbes and toxins

• opsonization of phagocytosis of microbes

• Antibody-dependent cellular cytotoxicity

• Lysis of microbes

• phagocytosis of microbes opsonized with complement fragments

• inflammation

• complement activation

Neutralization

• blocks binding of microbe and infection cells

• immobilization and adherence prevention

• antibody blocks adhesion molecules on bacterial surface

• inactivation of toxins and viruses

Opsonization

• facilitates removal of pathogen by phagocytes

• antibodies act as opsonins

• bind with antigens and mark pathogens to be destroyed by phagocytosis

Antibody Dependent Cellular Cytotoxicity (ADCC)

• allows host to selectively kill cells

• antibodies coat target cell by binding epitopes all over surface

• antibody stem binds to receptors on NK cells

Complement Activation

• stems of antibodies bind to complement protein, activating it

• activates complement pathway which releases inflammatory mediators

• results in opsonization and lysis of microbe

Immunological Memory

• subsequent exposure to antigen results in faster and more effective response due to memory

• basis of immunization