PowerPoint PresentationReview…Initial differen- tiation… ='s “thymic matura-tion”Initial differen- tiation… c-Kit (receptor for stem cell growth factor) CD44 (an adhesion molecule) CD25 ( chain of IL-2 receptor)Fundamental notion:Another fundamental notion…The effectEvidence for Positive selection & Negative selectionActivation…“Overview” (!)Some common themes in signal transduction…The co-stimulatory signalCo-Stimulatory Differences among Antigen Presenting Cells (APC’s)IMMUNOLOGYBios 328a textbook-based study of immunologySpring 2003http://www.lehigh.edu/~sk08/Courses/Bios328/mainpage.htmReview…Initial differen-tiation…='s “thymic matura-tion”Initial differen-tiation…c-Kit (receptor for stem cell growth factor)CD44(an adhesion molecule)CD25 ( chain of IL-2 receptor)Fundamental notion:Positive selection of thymocytes bearing receptors capable of binding self-MHC molecules which results in MHC restriction.Negative selection by elimination of thymocytes bearing high-affinity receptors for self-MHC molecules alone or self-antigen presented by self-MHC, which results in self-tolerance.Another fundamental notion…There are first “double negatives” (DN’s)…Then there are “double positives” (DP’s)….DN and DP refer to the presence of CD4 and CD8The effectNote what’s happening and whereEvidence for Positive selection & Negative selectionActivation…in the per ipher y…some key events:“Overview” (!)Some common themes in signal transduction…•The involvement of receptors•The generation of second messengers•The action of protein kinases and phosphatases•The induced assembly of critical components of a signal transduction pathway•Cascades•The involvement of large and small G proteins•The default setting for signal transduction is OFFThe co-stimulatory signalCo-Stimulatory Differences among Antigen Presenting Cells