CHARACTERIZATION OF A HUMAN-ANTIGEN WITH SERA FROM INFERTILE PATIENTS

We report the cDNA cloning and subsequent characterization of a novel antigen implicated in antibody-mediated human infertility. This antige n, designated AgX (unknown antigen), was identified originally by scre ening a human testis lambda gt11 cDNA expression library with infertil e patients' sera known to contain anti-sperm antibodies. AgX cDNAs iso lated from testis and placenta cDNA libraries (AgX-1 and AgX-2, respec tively) differed by a 48-bp deletion in the open-reading frame (ORF). The AgX-1 and AgX-2 ORFs encoded putative peptide chains of 505 and 52 1 amino acids (similar to 55.5 and similar to 57.3 kDa), respectively. The AgX amino acid sequences contained consensus motifs indicative of NTP binding. However, computer homology searches did not identify any significant similarity with known sequences. Quantitative analysis us ing the reverse transcriptase-polymerase chain reaction (RT-PCR) indic ated that the AgX-1 mRNA was fiftyfold more abundant than AgX-2 in the testis, while AgX-2 was more abundant than AgX-1 in somatic tissues. An anti-AgX peptide antiserum identified two AgX isoforms on Western b lots of human tissue extracts. An abundant 56-kDa isoform was detected only in testis and sperm. These data suggest that the 56- and 58-kDa isoforms are AgX-1 and AgX-2, respectively. AgX was localized by immun ofluorescence to the principal piece of the sperm tail. Therefore, ant ibodies against an AgX isoform may reduce fertility by affecting sperm function.