Biochemical and functional characteristics of the human leukocyte membrane antigen family LFA‐1, Mo‐1 and p!50,95

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Abstract
The human leukocyte function‐associated (LFA‐1) antigen, the monocyte differentiation antigen Mo‐1 which is characterized as the C3bi receptor and the glycoprotein p150,95 are characterized biochemically. Immunoprecipitations carried out with 6 different monoclonal antibodies (mAb) against LFA‐1 indicated that four mAb (SPV‐ L1, SPV‐L5, SPV‐L7 and SPV‐L11) were directed against the a chain, whereas mAb CLB54 and MHM‐23 were found to react with the common β chain of LFA‐1, Mo‐1 and p150,95. LFA‐1 and Mo‐1 expressed on KG‐1 cells or lymphocytes, monocytes and granulocytes from one donor were homogeneous. Interestingly the a chain of p150,95 showed heterogeneity. The molecular weight of the a chain expressed on monocytes was consistently higher than that of the α chain on granulocytes. The β subunits of LFA‐1 and Mo‐1 (as detected by mAb Bear‐1) are not only similar in molecular weight and isoelectric focusing patterns, but it is demonstrated here that they are also identically glycosylated and have similar protein backbones as judged by tryptic peptide mapping. In spite of their structural similarities, LFA‐1 and Mo‐1 differ completely in some of their biological functions. Anti‐LFA‐1 mAb strongly inhibited monocyte‐dependent T cell proliferation induced by tetanus toxoid or Helix pomatia hemocyanin and pokeweed mitogen‐driven specific antibody production in vitro, whereas the anti‐Mo‐1 antibody Bear‐1 was ineffective. These results suggest that the differences in these biological functions of LFA‐1 and Mo‐1 may be related to their different a subunits, which may recognize specific counter structures.

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