STB1, a mouse lymphocyte marker found on T cell and B cell subpopulations.

A set of monoclonal antibodies has been raised to cell surface markers which are either hyperexpressed, or exclusive to activated murine lymphocytes. One antigen is present on all B cells of the Ly1 lineage and defines a novel subpopulation of classical B cells, most of which are activated B cells. In Western blots, this antigen appears as a single glycoprotein of 95 kDa molecular weight but of greater interest, is its expression at high levels on all mature peripheral T cells but on only 30% of thymocytes. This marker is expressed at high levels on all CD4 and CD8 thymocytes, most double-negative (CD4-CD8-) thymocytes, and at low levels on double-positive (CD4+CD8+) thymocytes. It may prove useful as a developmental marker for subdividing the double-positive (CD4+CD8+) and double negative (CD4-CD8-) thymocyte populations. Taken together these results indicate that mab 3.17 recognises a novel lymphocyte antigen expressed on subsets of T and B cells, which is hyperexpressed on lymphocyte activation.