Date of Award
Doctor of Philosophy (PhD)
During the activation and differentiation of B cells, there are critical stages of regulation which determine the fate of the B cell. Resting B cells are initially stimulated by either native antigen or T cells via antigen-specific cell surface receptors. The context and timing of this signal induces either activation, tolerance or apoptosis of the B cell. If the initial signal productively activates the B cell, it acquires enhanced responsiveness to antigen independent signals, i.e. cytokines. The array of cytokines with which the B lymphoblast interacts induces proliferation and/or differentiation. We have studied several aspects of each of these stages in the B cell immune response. We compared the requirements for membrane immunoglobulinmediated tyrosine phosphorylation with the requirements for downstream signaling events. Our results demonstrate that receptor crosslinking is required for the accumulation of tyrosine phosphorylated proteins and for the induction of in vitro phosphotransferase activity of at least one kinase. The protein tyrosine kinase syk is one of the major endogenous substrates of this kinase acti vi ty. Moreover, we demonstrated that the in vitro phosphorylation of syk is induced synergistically by IL-4 and anti-immunoglobulin. We subsequently isolated a cDNA clone of human syk that, along with ZAP-70, defines a novel family of protein tyrosine kinases. We modeled the SH2 domains of syk to design a mutational analysis of the structure and function of syk. To facilitate the study of B cell responses to membrane immunoglobulin-independent signals, we devised a system of B cell activation dependent on a cognate interaction between B cells and allogeneic T helper cells. These allo-activated B blasts were unique in that IL-2 proved to be the predominant cytokine promoting their proliferation and Ig secretion, including high levels of Ig utilizing downstream heavy chain constant region genes. Both phenotypically and functionally, these B lymphoblasts resembled the germinal center B cell.
Forman, Mark S., "B Cell Activation: The Regulation by T Cells and the Induction of the Protein Tyrosine Kinase SYK" (1994). Student Theses and Dissertations. 356.