Some

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Some odds and ends

• Why are they odd?
• Maybe because they dont easily fit in the big
  picture.
• Lets look at the big picture

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?? - T-CELLS

• The initial impression is that they may not have
  much of an existence in the adult.

But is that impression true?
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?? - T-CELLS

• Lets locate these cells in the periphery.

The intraepidermal cell is a ?? T-cell that
expresses neither CD4 or CD8.
(Figure 2-23)
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?? - T-CELLS

• Lets locate these cells in the periphery.

The intraepithelial cell is a ?? T-cell that
expresses CD8 (but not CD4).
(Figure 2-22b)
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Another oddity SUPERantigens

• Que pasa aqui?

What happens when a SUPERantigen
is present? Depends if it is present in
the thymus or in the periphery.
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SUPERantigens

• If superantigens are in the thymus, they produce
  through clonal deletion holes in the
  repertoire.
• If superantigens are in the periphery, there is
  indiscriminate and extensive activation leading
  to shock.

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SUPERantigens

• If superantigens are in the thymus, they produce
  through clonal deletion holes in the
  repertoire.
• If superantigens are in the periphery, there is
  indiscriminate and extensive activation leading
  to shock.

These superantigens are often endogenous.
These superantigens are often exogenous.
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SUPERantigens

• If superantigens are in the thymus, they produce
  through clonal deletion holes in the
  repertoire.

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SUPERantigens

• If superantigens are in the periphery, there is
  indiscriminate and extensive activation leading
  to shock.

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OK, lets switch to B-cells and antibody
synthesis

• What is one of the most fundamental tenets?
• viz. that development of B-cells exists in
  antigen-independent and antigen-dependent phases.
• The antigen-dependent phase occurs in the lymph
  nodes.
• What happens in the paracortex (of lymph nodes)?
• ANSWER association with T-helper cells which
  migrate towards the cortex the B-cells then
  going to follicles.

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ANSWER association with T-helper cells which
migrate towards the cortex the B-cells then
going to follicles...

• But is such T-cell dependence universal?
• No.
• There are thymus-
• independent antigens (TI).

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There are two general sorts of thymus independent
antigens
Principal example LPS (bacterial
lipopolysaccharide)
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There are two general sorts of thymus independent
antigens
Principal example(s) Bacterial
capsules Bacterial flagella Mechanism extensive
cross- linking of mIg
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Some more surprises.

• How does a limited repertoire of antibodies
  defend against diverse invading antigens?
• British and Israeli scientists have shown that
  an antibody can exist in several conformations,
  each with its own binding specificity.
• The down side conformational diversity run
  rampant might contribute to autoimmunity and
  allergy.
• Take a look...