In order to investigate the origin of an 84-kDa protein with ABH blood-typi
ng 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 imm
unosorbent 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, o
n immunoblotting. The mean concentration of p 84 in seminal plasma was 949
mu g/ml (n = 54 subjects). There was no significant difference in the conce
ntration 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 signi
ficant correlations between the concentration of p 84 and the total seminal
protein concentration. An immunohistochemical study using mAb p 84 with li
ght microscopic detection showed that p 84 was located in the cytoplasm of
the inner layer of pseudostratified cuboidal epithelial cells of the semina
l vesicles, but no immunoreactivity was found in the prostate. These data i
ndicate that p 84 originates from a single tissue, the seminal vesicles, an
d suggest that p 84 is an ABH epitope-bearing protein that has not previous
ly been identified but possesses some immunological properties similar to t
hose of lactotransferrin.