Precolostral antibody reactivity against Histophilus somni conserved proteins and Escherichia coli whole cells in stillborn and live calves

Recent studies have demonstrated that neither the uterus nor the fetal gastrointestinal tract is sterile. We hypothesized that antibodies (Ab) that react with bacterial antigens are common in fetuses. Plasma samples from 121 stillborn calves were used as the experimental group and 21 live-born healthy calves were used as the control group. In precolostral plasma samples, IgG₁, IgG₂, and IgM Ab reactivity with Histophilus somni rHsp60 and rOMP40 proteins and Escherichia coli whole cells was tested by ELISA. Selected samples from stillborn and live-born calves were evaluated for antibody reactivity with E. coli antigens separated by SDS-PAGE to verify the recognized protein profile. To investigate whether the antibodies were of maternal origin or self-produced, the sera of the dams were evaluated by immunoblotting.

In calves, positive reactions to all antigens were detected by ELISA. In ELISA, the greatest variation in the results was observed for IgM class reactivity with selected proteins and the E. coli strain. Stillborn calves showed significantly greater reactivity in the IgG₁ subclass with only E. coli. Immunoblotting analysis revealed reactions of IgG₁ and IgM class Ab with E. coli antigens of different molecular weights, both in the control and stillborn groups. The reactivity of the tested calves was not identical to that of their mothers, indicating that the antibodies were self-produced by the calves during pregnancy.

These results suggest that calves are exposed to different Gram-negative bacteria during pregnancy, and that the stillborn group elicited diverse responses.