The presence of I-region-associated antigens on B cells in molecules distinct from immunoglobulin and H-2K and H-2D.

The distribution of I-region-associated antigenic specificities in murine lymphoid cells was studied by immunofluorescence. The antigens were mostly represented in B cells and in macrophages. The complexes of I-anti-I-region-associated antigens were found to be distributed throughout the lymphocyte surface both at 4 degrees and 37 degrees . In about two-thirds of the lymphocytes the complexes redistributed into caps after incubation with a second ligand (an anti-mouse immunoglobulin). The I-region specificities were in molecules distinct from immunoglobulin or from the molecules coded by the H-2K and H-2D regions.