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.
Anatomical and Functional Consideration of the Trigemino-Facial Nervous Communication and Facial Expresssion Muscles