Identification with a monoclonal antibody of a predominantly B lymphocyte-specific determinant of the human leukocyte common antigen. Evidence for structural and possible functional diversity of the human leukocyte common molecule.

Initial studies with the monoclonal antibody F8-11-13 described in this paper showed that it reacted strongly with B lymphocytes, did not react at all with granulocytes, and reacted only weakly with a small subpopulation of thymocytes and peripheral T lymphocytes. This picture was entirely different from that seen with monoclonal antibodies to the leukocyte common (LC) antigen, where 100% of all the above-mentioned leukocyte populations were positive. Biochemical studies using detergent solubilized membranes labeled with 3H at the sialic acid residues showed that the molecule bearing the F8-11-13 determinant was a glycoprotein of 215,000 mol wt, and that the peak depleted by F8-11-13 monoclonal antibody affinity columns corresponded to the high molecular weight region of a broad peak previously shown to be completely depleted by monoclonal antibody (F10-89-4) affinity columns directed at the LC antigen. Proof that the F8-11-13 determinant was expressed on some LC molecules was established by cross-inhibition studies with affinity-column-purified and depleted material. This finding of a serologically identifiable conformational or other structural change selectively expressed on the LC molecule of a functionally discrete population of lymphocytes has interesting implications for the structure and function of the LC molecule, and might be relevant to functional consideration of other membrane molecules.