Origin of an 84‐kDa Protein with ABH Blood‐Typing Antigen Activity in Human Seminal Plasma

Abstract

In order to investigate the origin of an 84‐kDa protein with ABH blood‐typing antigen activity (p 84) and its concentration in human seminal plasma, a monoclonal antibody (mAb p 84) was produced. The protein was recognized in breast milk as well as in seminal plasma by an indirect, enzyme‐linked immunosorbent assay (ELISA) using this mAb. mAb p 84 identified 84‐kDa and 83‐kDa forms of the protein in seminal plasma and breast milk, respectively, on immunoblotting. The mean concentration of p 84 in seminal plasma was 949 μg/ml (n = 54 subjects). There was no significant difference in the concentration of p 84 between individuals who secreted (Se) or did not secrete (non‐se) the ABH antigen into their seminal plasma, nor were there any significant correlations between the concentration of p 84 and the total seminal protein concentration. An immunohistochemical study using mAb p 84 with light microscopic detection showed that p 84 was located in the cytoplasm of the inner layer of pseudostratified cuboidal epithelial cells of the seminal vesicles, but no immunoreactivity was found in the prostate. These data indicate that p 84 originates from a single tissue, the seminal vesicles, and suggest that p 84 is an ABH epitope‐bearing protein that has not previously been identified but possesses some immunological properties similar to those of lactotransferrin.