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

The S100 proteins comprise a large sub-family of the EF-hand calcium-binding proteins. Here we describe a novel monoclonal antibody recognizing a B cell surface antigen. This monoclonal antibody immunoprecipitates three proteins in the 12-18 kDa range and the smallest of these proteins has a striking homology at its amino-terminus to human MRP8, a myeloid specific member of the S100 family. Similarly to MRP8 in myeloid cells, this antigen is expressed in the cytoplasm of B cells and is secreted by LPS-induced activated B cells. This surface antigen is not B cell specific. Since MRP8 is not expressed by lymphoid cells, however, this antibody appears to recognize a new member of the S100 family.