Epitopes of the Highly Immunogenic Trichomonas vaginalis α-Actinin Are Serodiagnostic Targets for Both Women and Men

There is a need for a point-of-care serodiagnostic test for women and men for sexually transmitted infections (STIs) caused by Trichomonas vaginalis. Sera from women with this STI and sera from men that were analyzed in studies showing a relationship between serostatus and prostate cancer are highly seropositive in response to trichomonad alpha-actinin and its truncated protein (ACT-P2) (positive control sera). Epitope mapping experiments showed that positive control sera from women had antibodies to 13 distinct epitopes, 5 of which were detected by positive control sera from men. Sera from women and men that were unreactive with alpha-actinin (negative control sera) failed to detect any of the epitopes or other alpha-actinin amino acid sequences. The T. vaginalis alpha-actinin amino acid sequence and the sequences of the epitopes showed little or no identity with those of other proteins of microbial pathogens or the human alpha-actinin 1 (HuACTN1) homolog. Immunoassays such as dot blot, immunoblot, and enzyme-linked immunosorbent assays were used. Positive control sera did not detect HuACTN1 in immunoassays, and the range of levels of identity of alpha-actinin epitopes with HuACTN1 was 0% to 50%. Comparison of the T. vaginalis alpha-actinin epitopes with proteins in data banks, such as Tritrichomonas suis, Candida albicans, and Saccharomyces cerevisiae proteins, gave a range of identity levels of 0% to 22%. Specific 15-mer peptide epitopes of alpha-actinin with low to no identity with other proteins were synthesized and were reactive with positive control sera only. These findings identify epitopes of alpha-actinin as candidate serodiagnostic targets and suggest strongly that a highly seropositive reaction to alpha-actinin suggests exposure to T. vaginalis.