This study was conducted to investigate the effect of vaccinating mares against melatonin on seasonal reproductive cycles. Melatonin-Bovine serum albumin (Mel-BSA) conjugate, mixed with a Quil A based adjuvant was utilized to immunize the mares during the anestrous season of two consecutive years (November, 1997–May, 1998, and November, 1998–May, 1999). In year 1, mares were vaccinated 4 times beginning in November at 1 week, 3 week and 3 week intervals with low antigen dose (0.25, 0.5, 0.5, 0.5 mg Mel-BSA per mare, n = 7), high antigen dose (2.5, 5.0, 5.0, and 5.0 mg Mel-BSA per mare, n = 6), control (0.25, 0.5, 0.5, 0.5 mg BSA per mare, n = 4) or none (no injection, n = 1). In year 2, mares were re-vaccinated 3 times beginning in November at 3 week, 3 week and 4 week intervals with 0.5 mg of Mel-BSA (n = 11) or BSA alone (n = 6). The seasonal reproductive cycles were evaluated by measuring serum progesterone concentration with ELISA and by following the ovarian activity using transrectal ultrasonography. In Year 1, the progesterone production patterns, percentage of cycling mares, the winter anestrous length, and the beginning of vernal transition (BVT) were similar between the treatment and control groups. However, in year 2 the progesterone production patterns in the treatment group was altered; 2 mares out of 11 were cycling throughout the winter and the percentage of cycling mares in the treatment group increased compared with the control; there was significant difference between the treatment and control groups in winter anestrous length (p < 0.05) and in BVT (p < 0.05) Anti-melatonin antibodies could directly neutralize circulating melatonin and block melatonin binding to its receptors on equine lymphocyte cell membrane (Kd = 172.9 ± 10.8 pM) and on equine pineal gland cell membrane (Kd = 139.2 ± 11.2 pM) in vitro. The results of this study demonstrated that vaccinating mares against melatonin could after the seasonal reproductive cycle, and the mechanisms underlying this effect likely include neutralization of circulating melatonin and the blockade of melatonin binding to its receptors by specific antibodies.

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Brucella abortus is a facultative intracellular gram-negative bacterium that causes chronic protracted infections of humans and livestock. It is also a potential biowarfare agent and thus development of vaccines for humans is an important goal. In mice infected with Brucella abortus, protective roles for CD4 and CD8 T cells have been demonstrated. A critical role for T cells is likely to be production of IFNγ as IFNγ-deficient mice succumb to brucellosis. Here we show both T cell subsets contribute to control of infection by virulent strain B. abortus 2308 by producing IFNγ and CD4 T cells but not CD8 T cells facilitate clearance of infection. Strikingly, antibody-independent B cell functions contribute to the development of the high plateau phase of infection as both B cell/antibody-deficient C57BL/6 and BALB/c mice cleared 99% of the infection by 2 weeks in an antibody-independent manner. Further characterization of the immune response revealed that B cells produced regulatory cytokines in both C57BL/6 and BALB/c mice. B cells from C57BL/6 mice produced IL-10 while B cells from BALB/c mice produced TGF-β, which in turn can dampen protective IFN-γ mediated immune responses. Consequently, clearance of infection in B cell deficient C57BL/6 mice coincided with a decrease in IL-10 and an increase in the proportion of IFNγ-producing T cells while the clearance of infection in B cell deficient BALB/c mice was associated with a decrease in TGF-β producing cells and CD4 T regulatory cells. Due to the rapid clearance of infection in B cell deficient mice, we tested whether B lymphocytes act as an infection niche for brucellae and found that IgM and complement-opsonized viable B. abortus were phagocytosed by and survived within B lymphocytes in vitro. Furthermore, live brucellae were harbored within B lymphocytes in infected mice and these cells transferred disease to uninfected animals. Throughout the infection, a greater proportion of infected B lymphocytes produced TGFβ compared to non-infected B cells. Thus, B lymphocytes contribute to chronic brucellosis, and possibly other diseases, by providing an intracellular niche that can shield the bacteria from the host immune system and dampen inflammatory responses needed to clear the infection.

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