The structural and functional relations between the α- and β-subunits of the human lymphocyte function-associated antigen (HLFA) and the human Mac-1 antigen (HMac-1) have been analyzed with the use of five monoclonal antibodies that react with these proteins. The specificities of these antibodies were examined by immunoprecipitation of proteins from 125I-labeled cells and purified HLFA and HMac01 antigens. Three antibodies reacted with the Mr 95,000 common β-subunit of the proteins, and also co-precipitation the Mr 175,000 HLFA α-subunit, the Mr 165,000 HMac-1 α-subunit, and a third polypeptide α-subunit of Mr 150,000. The other antibodies were specific to noncross-reactive epitopes present on the α-subunit of HLFA or HMac-1. These specificities were confirmed in sequential immunoprecipitation studies. Peptide mapping showed that the β-subunits of HLFA and HMac-1 were identical, whereas the two α-subunits differed considerably. The HLFA α-subunit-specific monoclonal antibody inhibited phytohemagglutinin stimulation, the mixed lymphocytes reaction, cytolytic T lymphocyte-mediated killing, and tetanus toxoid stimulation, but did not affect natural killer cell-mediated killing or complement receptor type 3 function. The HMac-1 α-subunit-specific monoclonal antibody inhibited complement receptor type 3 function but had no effect on T cell or natural killer cell functions. Three monoclonal antibodies to the β-subunit inhibited all functions tested, including T cell, natural killer cell, and complement receptor type 3 activities. The results suggested that the functions of the HLFA and HMac-1 molecules may be determined by the α-subunit, and the common β-subunit also bears functionally important epitopes.
|Original language||English (US)|
|Number of pages||9|
|Journal||Journal of Immunology|
|State||Published - 1985|
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