Inhibition of Th1 responses in BLV-infected pregnant cattle.
To reveal the association of parturition with the progression of BLV infection, in this study, we focused on the immunosuppressive function of PGE2, which is also an important factor for the induction of parturition in pregnant animals. To investigate whether PGE2 is involved in immune dysfunction in pregnant cattle, we examined the PGE2 kinetics and Th1 responses of BLV-infected pregnant cattle (Figures 2a–2c and Supplemental Figures 1a–1c). Compared to the samples collected about 2 weeks before the parturition (Pre, day −17–day −12), PGE2 concentrations in sera were significantly increased on the day of parturition (day 0, Figure 2a). In contrast, Th1 responses against Con A were significantly suppressed on day 0 (Figure 2b). Th1 responses against BLV-antigen tended to be suppressed on day 0 (Figure 2c). Our previous studies have demonstrated that PGE2 suppresses the production of Th1 cytokines from bovine PBMCs, and the inhibition of PGE2production using a COX-2 inhibitor activates BLV-specific Th1 responses [16, 17]. Taken together, these results suggest that PGE2 induction before delivery is associated with the inhibition of Th1 responses in pregnant cattle.