CHARACTERIZATION OF MOUSE CD6 WITH NOVEL MONOCLONAL-ANTIBODIES WHICH ENHANCE THE ALLOGENEIC MIXED LEUKOCYTE REACTION

Human CD6 is a cell surface protein expressed by thymocytes, mature T cells, a subset of B cells and certain cells of the brain. On human T cells, CD6 has been shown to act as a co-stimulatory molecule which mo dulates T cell receptor (TCR)-mediated T cell activation. To study Fur ther the recently identified mouse CD6 (mCD6), we generated and charac terized a set of anti-mCD6 mAb. Anti-mCD6 mAb recognizing the mCD6 sca venger receptor cysteine-rich (SRCR) extracellular domains 1 and 3 wer e identified. mAb against SRCR domain 3, but not domain 1, inhibited t he interaction of CD6 with a recently identified ligand. activated leu kocyte cell adhesion molecule (ALCAM). Immunohistochemical analysis in dicated that mCD6 expression was largely localized to the T cell areas of lymphoid tissue and, as previously reported in the human, CD6 was also expressed by neurons. CD6 was highly expressed on mouse T cells i solated from the spleen, lymph node and thymus as demonstrated by two- color immunofluorescence analysis. The CD4(-) and CD8(+) cells in thes e lymphoid compartments expressed similar levels of CD6. Immunoprecipi tation studies showed mouse thymocytes predominantly express a CD6 iso form of similar to 130 kDa. while splenocytes predominantly express a CD6 isoform of similar to 100 kDa. Anti-mCD6 mAb enhanced allogeneic m ixed leukocyte reactions (MLR). indicating that CD6-ALCAM interactions may regulate the proliferative capacity of T cells.