Characterization of a B cell surface antigen with homology to the S100 protein MRP8

A novel activation induced lymphocyte surface antigen, 90.12, is also expressed on apoptotic cells

We describe a monoclonal antibody, mAb 90.12, which recognizes a novel activation induced lymphocyte surface antigen. Flow cytometric analysis of normal tissues shows the antigen to be expressed on higher percentages of B lymphocytes in the bone marrow than in the spleen and the lymph node. Similarly, the 90.12 antigen is expressed on higher percentages of thymocytes than peripheral T cells. MAb 90. 12 immunoprecipitates three proteins with a molecular weight of 12-18 kDa which are not linked to the membrane by phosphotidylinositol. Expression of the 90.12 antigen is increased on activated B cells and the extent of upregulation varies with the stimulus. Lipopolysaccharide (LPS) stimulation results in expression on most B cells, while expression is upregulated on only a subset of B cells stimulated with anti-immunoglobulin M (IgM), interleukin(IL)4 and IL5. Finally, we show that 90.12 antigen expression is also increased on apoptotic cells.