VP4-Specific IgA level as a correlate of neutralizing antibody and fecal shedding of porcine rotavirus infection.

Rotavirus (RV) causes diarrhea in children, infants, and young animals globally, with public health implications. Porcine rotavirus (PoRV) leads to economic losses in swine farming. Neutralizing antibodies (NAb) are vital for protecting piglets from intestinal infections. However, which serum and mucosal markers correlate with NAbs against PoRV and relate to post-infection fecal shedding remains unclear, crucial for pathogen-specific detection. We used indirect ELISA to measure IgG/IgA in sera, sIgA in colostrum from recovered pigs, and feces from diarrheal piglets against VP4*, VP7*, VP6, and NSP4*. Analyses showed specific IgA/sIgA levels correlated better with NAb titers than IgG. Among them, VP4*-specific IgA/sIgA had the highest positive correlation with NAb titers in sera (R = 0.848, P < 0.0001) and colostrum (R = 0.865, P < 0.0001). Also, VP4*-specific IgA/sIgA in sera (R= -0.446, P < 0.001) and feces (R= -0.497, P < 0.0001) had the strongest inverse relationship with viral RNA load. Piglet passive protection tests confirmed VP4*-specific IgA's high neutralizing capacity, highly correlated with NAb titers (R = 0.858, P < 0.0001), reducing viral shedding. In conclusion, mucosal IgA/sIgA responses to VP4 are important for PoRV diagnosis assays and vaccine efficacy evaluation.