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Delve into the world of T-cells, B-cells, and superantigens to uncover their roles and interactions in the immune system. Explore the oddities and intricacies of these components, from T-cell localization to B-cell development, and the impact of superantigens on immune responses. Learn how limited antibody repertoires defend against diverse antigens, and the potential implications of antibody conformational diversity on autoimmunity and allergies.
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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 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-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… “SUPERantigens” ¿Que pasa aqui? What happens when a SUPERantigen is present? Depends if it is present in the thymus or in the periphery.
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.
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.
SUPERantigens… • If superantigens are in the thymus, they produce — through clonal deletion — “holes in the repertoire.”
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… • 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.
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… Principal example: LPS (bacterial lipopolysaccharide)
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…. “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...
