Association of antisperm antibodies with conception and molecular mimicry between spermatozoal and genital bacterial proteins in crossbred cows

Antisperm antibodies (ASA) have been implicated in reproductive failure in cows. Present study investigated 58 crossbred cows, of which 38 (normal-cows, NC, n = 16; repeat-breeder-cows, RBC, n = 22) were used for ASA analyses and fertility evaluation, while subsequent bacteriological component included additional 20 cows. ASA levels were assessed from maiden to conceptional-estrus using mixed-antiglobulin reaction (MAR-IgG and MAR-IgA) tests and ELISA, and candidate spermatozoal-bacterial protein pairs were assessed for sequence and three-dimensional structural similarity. MAR-IgG and MAR-IgA levels were significantly lower during conceptional-estrus than during maiden-estrus in both NC and RBC cows, whereas differences between NC and RBC at same estrus stage were less pronounced, indicating that ASA levels were closely associated with conception status than with fertility classification. Receiver operating characteristic analysis based on cow-level measurements showed that MAR-IgG and MAR-IgA discriminated conceptional from non-conceptional status, with area under the curve values of 0.799 and 0.806, respectively. Head-bound spermatozoa represented predominant antibody binding, suggesting that sperm head antigens constitute major ASA targets. Bacillus spp., Escherichia coli and Staphylococcus spp. were predominant bacterial isolates recovered from the genital tract. Sequence and structural analyses of previously identified cross-reactive sperm and bacterial proteins revealed substantial peptide-level similarity and structural-overlap, and structural-superimposition produced low root mean square deviation values, indicating close structural similarity between sperm and bacterial proteins. Collectively, these findings indicate that lower ASA levels are associated with successful conception and support molecular mimicry between genital bacterial and sperm proteins as a plausible mechanism contributing to reproductive immunoinfertility in cows.