Immunogenetic studies of soluble Fc receptor (CD16) antigens in human seminal plasma

Two forms of CD16 Fc receptors (FcRIII) have been defined on human leukocytes. Type 1, present on polymorphonuclear neutrophils (PMN), expresses the NA alloantigen system and type 2, present on natural-killer (NK) cells and macrophages, has no known polymorphic variations. We have described the presence of soluble FcRIII antigens in human seminal plasma (SP). These SP antigens retain an affinity for IgG-Fc and are biochemically distinct from leukocytic FcRIII. Their origin within the male reproductive tract and how they relate to FcRIII types 1 and 2 were not known. By using monoclonal antibodies CLB/Gran 11 and Leu 11c that differentially react with FcRIII type 1 and type 2 from different individuals, we studied how SP FcRIII antigens relate to leukocytic FcRIII. CLB/Gran 11 and Leu 11c reactivities with PMN and NK cells from a selected panel of male donors were compared with enzyme-linked immunosorbent assay reactivities of CLB/Gran 11 and Leu 11c with SP samples from these donors. The reactivity pattern with SP samples was shown to be different from findings with donors' PMN, but it corresponded with their NK cells. Our results indicate that SP FcRIII antigens do not manifest the polymorphic variations that are detected by CLB/Gran 11 and Leu 11c on PMN. These findings suggest that SP FcRIII antigens do not originate from PMN.