Adaptive immunity in the postpartum uterus: Potential use of vaccines to control metritis

After parturition, dairy cows rely on an effective innate immune response, through the actions of neutrophils, macrophages, and antimicrobial peptides, to clear the uterus from pathogenic bacteria, such as E. coli, Bacteroides spp, F. necrophorum and T. pyogenes. However, the role of adaptive immunity in the postpartum uterus is less understood. In this review, we explore concepts of mucosal adaptive immunity and discuss recent findings regarding the efficacy of vaccines to reduce metritis in dairy cows. Areas of lymphocytic aggregates are seen throughout the bovine reproductive tract after parturition, but it is unknown if their development is influenced by previous exposure to pathogens or other intrinsic factors. Through the actions of Treg cells and γδ T cells, the uterus is an immune-tolerant environment during pregnancy. After parturition, the dynamics in the endometrial and circulating lymphocytic populations differ among cows that develop uterine diseases and healthy counterparts. However, the functionality of those cells has not yet been determined. It has been hypothesized that cows that fail to switch their uterine environment from an anti-inflammatory state prior to parturition to a pro-inflammatory state after calving are more susceptible to uterine infections. Given the nature of metritis related pathogens and the importance of innate immunity to uterine defense mechanisms, we speculate that an adaptive immunity biased towards a Th1/Th17 cellular response will provide best protection against uterine infections. Few studies have evaluated the efficacy of immunization in reducing the incidence of metritis in dairy cows revealing inconsistent findings.