Late pregnancy is associated with an increase in regulatory cytokines and a decline in nematode-specific antibody levels in sheep infected with Teladorsagia circumcincta.

The gastrointestinal nematode Teladorsagia circumcincta is a prevalent and economically important parasite of sheep. Sheep develop acquired immunity to T. circumcincta, characterised by nematode-specific antibody production and a type 2 T-helper (Th) cell response. During late pregnancy and early lactation, ewes experience increased nematode faecal egg count (FEC) known as the peri-parturient rise (PPR). The PPR is associated with a decline in nematode-specific antibodies, but research on the role of Th cell-mediated immunity in the PPR is limited. Here, we characterised the cellular and humoral immune responses of T. circumcincta-infected ewes fed at two dietary levels during the peri-parturient period. Diet had a limited effect on any trait, likely due to the high body condition of the ewes entering the study, but all ewes experienced a pronounced PPR. The PPR was associated with a decline in nematode-specific IgG, and antigen-dependent declines of IgA and IgE around parturition. Levels of the Th1-associated cytokine IFN-γ and the Th2-associated cytokine IL-4 showed antigen-dependent declines during the peri-parturient period. In contrast, the regulatory cytokine IL-10 increased around parturition in response to a generic mitogen, nematode antigens and Heptavac® vaccine, suggesting a generalised regulatory immune phenotype. Our results provide a comprehensive view of the immunological changes during the PPR and suggest a possible role for regulatory T cell responses.