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
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Clonal selection
CD 4
CD 8
Epitope
Endogenous antigen
Exogenous antigen
Phagolyzosome
Characteristics of Adaptive
Immunity
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Antigenic specificity
Diversity
Immunologic memory
Self recognition
Interface with Innate Immune
System
 Phagocytosis
 Inflammation
Major Cells of Adaptive Immunity
 Lymphocytes
 B
 T
 TH
 TC
 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
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Membrane bound antibody
TCR
MHC I
MHC II
Lymphocyte Diversity
 Random rearrangement of gene
segments
 1010 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
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Occurs in Secondary lymphoid organs
Specificity of all progeny is identical
Explains secondary response
Memory cells more numerous than
naïve cells