PowerPoint PresentationSome “odds and ends”… - T-CELLSSlide 4Slide 5Another oddity… “SUPERantigens”SUPERantigens…Slide 8Slide 9Slide 10OK, let’s switch to B-cells and antibody synthesis…ANSWER: association with T-helper cells which migrate towards the cortex; the B-cells then going to follicles...There are two general sorts of thymus independent antigens…Slide 14Some more surprises….IMMUNOLOGYBios 328a textbook-based study of immunologySpring 2003http://www.lehigh.edu/~sk08/Courses/Bios328/mainpage.htmSome “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-CELLSThe initial impression is that they may not have much of an existence in the adult.But is that “impression” true? - T-CELLSLet’s locate these cells in the “periphery.”The intraepidermalcell is a  T-cellthat expressesneither CD4 or CD8.(Figure 2-23) - T-CELLSLet’s locate these cells in the “periphery.”The intraepithelialcell is a  T-cellthat expressesCD8 (but not CD4).(Figure 2-22b)Another oddity… “SUPERantigens”¿Que pasa aqui?What happens whena SUPERantigen ispresent?Depends if it is present in thethymus or in theperiphery.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 capsulesBacterial flagellaMechanism:extensive cross- linking of mIgSome 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