Some odds and ends
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Some “odds and ends”…. Why are they “odd”? Maybe because they don’t easily fit in the “big picture.” Let’s look at the “ big picture ”.  - T -CELLS. The initial impression is that they may not have much of an existence in the adult. But is that “impression” true?.  - T -CELLS.

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Some “odds and ends”…

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Some odds and ends

Some “odds and ends”…

Why are they “odd”?

Maybe because they don’t easily fit in the “big picture.”

Let’s look at the “big picture”


T cells

 - T-CELLS

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

But is that “impression” true?


T cells1

 - T-CELLS

Let’s locate these cells in the “periphery.”

The intraepidermal

cell is a  T-cell

that expresses

neither CD4 or CD8.

(Figure 2-23)


T cells2

 - T-CELLS

Let’s locate these cells in the “periphery.”

The intraepithelial

cell is a  T-cell

that expresses

CD8 (but not CD4).

(Figure 2-22b)


Another oddity super antigens

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.


Superantigens

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.


Superantigens1

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.


Superantigens2

SUPERantigens…

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


Superantigens3

SUPERantigens…

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


Ok let s switch to b cells and antibody synthesis

OK, let’s 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.


Some odds and ends

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).


There are two general sorts of thymus independent antigens

There are two general sorts of thymus independent antigens…

Principal example:

LPS

(bacterial lipopolysaccharide)


There are two general sorts of thymus independent antigens1

There are two general sorts of thymus independent antigens…

Principal example(s):

Bacterial capsules

Bacterial flagella

Mechanism:

extensive cross- linking of mIg


Some more surprises

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...


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