We have continued our studies of the mechanisms of B cell activation, proliferation, and differentiation at the molecular and cellular levels. We have isolated a cDNA clone for the B cell membrane antigen CD22 and have shown that it functions to mediate B-B cell interactions and may be in part responsible for the maintenance of B cell enriched regions in lymphoid tissues. It is referred to as BL-CAM an acronym for B lymphocyte cell adhesion molecule. The CD20 promoter has been sequenced and CAT constructs spanning 4 kb 5 prime to the transcriptional start site have been made. These CAT constructs have been used to transfect B and T cell lines and a region necessary for B cell specific expression has been mapped. Current studies are devoted to determining the precise cis element(s) necessary for B cell specific expression. We have isolated 3 homeotic genes which are expressed in activated B cells. One of the genes, HB24, encodes for a protein with a homeobox highly related to a drosophila homeodomain, H2. These genes are likely to have important regulatory roles in certain developing tissues and in lymphocytes. Both in vivo and in vitro activated B cells have been found to secrete TNF-alpha and IL-6 and their production has been shown to be important in B cell function. TGF-beta has been shown to markedly inhibit the production of kappa and lambda light chain in B cells. The decrease in light chain mRNA is not accompanied by changes in 3 transcriptional factors (Oct-2, NF-kB, and kE2 binding proteins) known to be important in kappa transcription. TGF-beta did decrease AP-1 levels both in normal B cells and in B cell lines. We have begun to study the role of phosphatases in B and T cell activation and have found okadaic i acid, a specific phosphatase inhibitor, to be a potent activator of NF-kB, AP-1, and TNF-alpha mRNA (only B cells). Studies in collaboration with the metabolism branch and the Laboratory of Chemoprevention have demonstrated an increased production of TGF-beta by leukemic cells from patients with adult T cell leukemia. The increase in TGF-beta may be related to the transactivation of the TGF-beta promoter by the HTLV-1 p4Ox (TAX) protein. The cis response element in the TGF-beta promoter was mapped to two AP-1 sites known to be important in the autoinduction of TGF-beta. Finally we have demonstrated the production of potent vasoactive peptides, endothelin-1 and -3, by human macrophages and monocytes. Macrophage derived endothelins may be important regulatory factors which function within the macrophage microenvironment.
