Physical barriers to pathogens

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Physical barriers to pathogens Innate and
adaptive immunity Humoral and cellular
immunity Primary lymphoid tissue Secondary
lymphoid tissue Cells of the immune system
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Innate immunity phagocytosis and
inflammation rapid not antigen
specific antigen-specific memory is not
elicited macrophage activation is induced by
interaction of microbial products with cell
surface receptors (toll-like receptors,
CD14) cytokines play an important role
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• Vacuoles containing bacteria that have been
  engulfed fuse with lysosomes, which contain
  lysosomal enzymes - this results in the
  degradation of the engulfed microbe.

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• The interactions between microbes and macrophages
  also result in the rapid production of cytokines,
  soluble signaling molecules this triggers an
  inflammatory response (the local accumulation of
  fluid, plasma proteins, and WBC)

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pro-inflammatory cytokines
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Adaptive immune responses Antigen-specific Not
as rapid as innate responses, on initial response
to antigen However, much more rapid and
amplified responses on secondary exposure to the
same antigen (memory, amplification) Involves
recognition of antigen by T and B cell receptors
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Structure of T and B cell receptors Recognition
of antigen by T and B cell receptors Generation
of antigen-binding diversity in T and B cell
receptors Clonal selection Antigen-presenting
cells MHC molecules
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Cytokines Cytokine receptors
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Initial stages of B cell development are not
driven by contact with antigen (antigen-independen
t) Rearrangements that result in functional H-
and L-chains occur in a specific
order Elimination of self-reactive B
cells Antigen-driven B cell activation Different
iation to antibody-secreting (plasma) cells
Germinal center development Somatic
hypermutation Ig isotype switching
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Phase 1 development of B cells in bone marrow
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• The rearrangements that result in functional H-
  and L-chains occur in a specific order

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• These germinal centers (GC) contains
• proliferating (D - centroblasts) B cells
• differentiating (L - centrocytes) B cells

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T cell development Rearrangement of TCR genes in
T cell development Positive selection Negative
selection Antigen-driven T cell activation
Primary stimulatory signal (via
TCR) Secondary, co-stimulatory signals
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However, if b is rearranged first, then the T
cell continues to proliferate, and undergoes
further rearrangements. This results either in
rearranged a TCR gene, yielding an ab TCR lineage
cell, or rearranging g and d genes, resulting in
a gd TCR cell.  
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T cell subsets CD4 and CD8 cells Helper T
cells Helper T cell subsets TH1 and TH2
cells Cytotoxic T cells (CTL)
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NK cells Complement Acute-phase response
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Immune surveillance theory Oncogenic viruses -
interactions with immune system Tumor-specific
antigens Tumor-associated antigens
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Autograft Syngeneic transplants Allograft or
allogeneic transplants Immunosuppressive drugs