Mechanisms of MHCII signaling in B lymphocytes

During the initiation of an antigen-specific immune response, peptide fragments originating from the antigen are presented in complex with MHC class II glycoproteins (MHCgpII) on the surface of the antigen presenting cells (APC). Antigen recognition by T lymphocyte is accompanied by the formation of the molecular structure at the interface with APC called immunological synapse (IS). During this contact, signal transduction is initiated at both, T lymphocyte and APC, sides of the IS. For a long time it was thought that the only function of MHCgpII is presentation of antigen. However, later it was found that stimulation of MHCgpII led to triggering of signals contributing to decision about the further fate of APC. MHCgpII do not have any signaling motifs in their cytoplasmatic domains, and so associated molecules are necessary for the transduction of the signals. This work focuses on B lymphocytes in which the associated molecules are Ig alfa/beta, MPYS, CD19 and CD20. After the stimulation of MHCgpII these proteins mediate signaling events including activation of several families of protein kinases, phospholipase C, mobilization of calcium and activation of transcriptional factors NFAT and AP-1. In B lymphocytes, activities of these pathways may result in proliferation and differentiation but also in the..