Antigen Processing in Adaptive Immunity

Adaptive immunity

• body’s ability to recognize and create defenses against invaders

• carried out by lymphocytes that act against specific pathogens

• Cell-mediated (T cells) = act against intracellular pathofens

• Antibody-mediated (B cells) = act against extracellular pathogens

Specificity

• each response acts against one specific antigen

Inducibility

• cells of adaptive immune system respond to specific pathogen

Clonality

• adaptive immune cells proliferate to form many generations of nearly identical cells

Unresponsiveness to self

• does not act against normal body cells

Memory

• adapts to respond faster and more effectively in subsequent encounters with a particular pathogen or toxin

Natural Active Immunity (acquired)

Natural exposure to antigen induces immune response

Natural Passive Immunity (acquired)

transfer of antibodies or cells produced by others

• antibodies of mother transferred to infant across placenta or milk l

Artificial Active immunity (acquired)

deliberate exposure to antigen induces immune response

• vaccination

Artificial Passive immunity (acquired)

Antibodies in immune serum are introduced into the body

Antigens

• portions of cells or viruses that the body recognizes as foreign

• body recognizes the epitope, the 3D shape

Major Histocompatibility Complex (MHC)

• glycoproteins in membranes of most vertebrate cells

• present antigens to immune cells

• specificity determines which antigens trigger immune response

Antigen Presenting Cells (APC)

• present antigens to cells of adaptive immune system

• antigens must be processed to isolate epitopes before they can be displayed

Endogenous Antigen processing

• cell breaks down its own internal proteins

• polypeptide catabolized into epitopes

• epitopes are loaded onto complementary Class I MHC proteins

• MHC I protein-epitope complex will be displayed on cytoplasmic membrane of cells

Exogenous Antigen Processing

• APCs capture foreign pathogens using phagocytosis

• epitopes bind to MHC II proteins

• MHC II protein-epitope complex are displayed on APC membrane surface