We have continued our studies of the mechanisms of B lymphocyte activation, proliferation, and differentiation at both the molecular and cellular levels. Studies of the role of soluble factors in the regulation of B and T cell activation have been continued with a particular emphasis on several cytokines which are made by B cells themselves. Studies of the role of transforming growth factor-B (TGF-Beta) in the regulation of B cell immune function have progressed and we have shown that exposure to TGF-Beta markedly impairs the transcription of kappa and lambda light chain. Our studies with B minus T subtracted cDNA clones have progressed. Initial studies investigating the expression and probable function of one of the subtracted clones, BL-CAM, have been completed. Current studies are directed at mapping the transcriptional start site(s) and preparing constructs to study the promoter. Three other subtracted clones are in various stages of analysis. We are also isolating B cell genes which are expressed either exclusively or predominantly in the germinal center region. We have largely completed the analysis of the CD20 promoter and have characterized a site in the promoter which confers B cell specific expression on a minimal promoter. We have continued studies with 3 human homeobox containing genes; HOX 2.3., HB24, and HB9. Initial sequencing and expression studies with HB9 and HB24 have been completed. Human genomic clones for HB9 and HB24 have been isolated and partially sequenced. A mouse genomic clone for HB9 has been isolated and will be used for homologous recombination experiments. Screening of a mouse B cell cDNA library with the human HB9 and HB24 cDNAs resulted in the isolation of 3 cDNA clones which are related to either HB9 or HB24, but each identifies a distinct gene. The overexpression of HB24 in Jurkat cells resulted in the induction of an activation phenotype. Besides activated lymphocytes HB9 and HB24 are expressed in bone marrow progenitor cells and differentiation along specific lineages results in disappearance of HB24 and HB9 mRNA. Studies with the human HB9 and HB24 cDNA probes have revealed expression of murine and Drosophila homologs during embryogenesis. We have completed studies examining the effects of inhibiting certain specific phosphatases in lymphocytes on the expression of the transcription factors AP-1 and NF-KappaB; and the cytokine TNF-Alpha. Studies with the vasoactive peptide endothelin have shown the presence of endothelin receptors on mast cells in addition to the production of endothelin by these cells. The production of endothelin by astrocytes is partially regulated by endothelin itself since it can induce peptide secretion.
