Principles of Immunology Overview of Adaptive Immunity 1/24/06 “Too many people overvalue what they are not and undervalue what they are.” M Forbes

Adaptive Immunity  Specific host defenses that are mediated by B and T lymphocytes following exposure to antigens, and exhibit diversity and memory.

Word List  Clonal selection  CD 4  CD 8  Epitope  Endogenous antigen  Exogenous antigen  Phagolyzosome

Characteristics of Adaptive Immunity  Antigenic specificity  Diversity  Immunologic memory  Self recognition

Interface with Innate Immune System  Phagocytosis  Inflammation

Major Cells of Adaptive Immunity  Lymphocytes B T  T H  T C  Antigen presenting cells (APCs) Dendritic cells Macrophage B lymphocytes

B Lymphocytes  Originate and mature in bone marrow  Membrane bound antibody  Ag binding triggers division and differentiation  Progeny Plasma cells Memory B cells

T Lymphocytes  Mature in thymus  T cell receptors  MHC restriction Class I  Nucleated cells  Reacts with CD8 Class II  APCs  Reacts with CD4

T Lymphocytes(cont’d)  Progeny cells T helper  CD4  Class II restricted  Stimulates B and T cells (helper function) T cytotoxic  CD8  Class I restricted  Further differentiates CTLs(killing function) Memory T cells

Antigen Presenting Cells  Dendritic cells MHC I and II on surface Ag is internalized Stimulates T-helper cells  Macrophages  B lymphocytes

Humoral Immunity  Conferred via serum (cell-free) Antibody dependent Antibody functions  Enhanced elimination  Neutralization  C fixation/lysis

Cell-mediated Immunity  Conferred via lymphocyte exchange Cell dependent Modulates humoral immunity Cytotoxic

Antigen Recognition  Epitopes B cells recognize epitopes alone T cells require MHC association  Major molecules involved Membrane bound antibody TCR MHC I MHC II

Lymphocyte Diversity  Random rearrangement of gene segments potential specificities “Mature” lymphocytes are said to be “committed”

Antigen Processing  Exogenous antigens Phagocytosis Degradation Ag peptide/MHC II recognized by T helper  Endogenous antigens Viral or tumor induced Complexes with Class I Recognized by CTLs

Clonal Selection  Occurs in Secondary lymphoid organs  Specificity of all progeny is identical  Explains secondary response  Memory cells more numerous than naïve cells