[Show abstract][Hide abstract] ABSTRACT: Previous studies have suggested that currently available brucellosis vaccines induce poor or no protection in elk (Cervus elaphus nelsoni). In this study, we characterized the immunologic responses of elk after initial or booster vaccination with Brucella abortus strains RB51 (SRB51) and 19 (S19). Elk were vaccinated with saline or 10(10) CFU of SRB51 or S19 (n=seven animals/treatment) and booster vaccinated with a similar dosage of the autologous vaccine at 65 weeks. Compared to nonvaccinates, elk vaccinated with SRB51 or S19 had greater (P<0.05) antibody responses to SRB51 or S19 after initial vaccination and after booster vaccination. Compared to nonvaccinated elk, greater (P<0.05) proliferative responses to autologous antigen after initial vaccination occurred at only a few sample times in SRB51 (6, 14, and 22 weeks) and S19 (22 weeks) treatment groups. In general, proliferative responses of vaccinates to nonautologous antigens did not differ (P>0.05) from the responses of nonvaccinated elk. Gamma interferon production in response to autologous or nonautologous Brucella antigens did not differ (P>0.05) between controls and vaccinates after booster vaccination. Flow cytometric techniques suggested that proliferation occurred more frequently in immunoglobulin M-positive cells, with differences between vaccination and control treatments in CD4+ and CD8+ subset proliferation detected only at 22 weeks after initial vaccination. After booster vaccination, one technique ([3H]thymidine incorporation) suggested that proliferative responses to SRB51 antigen, but not S19 antigen, were greater (P<0.05) in vaccinates compared to the responses of nonvaccinates. However, in general, flow cytometric and other techniques failed to detect significant anamnestic responses to autologous or nonautologous Brucella antigens in S19 or SRB51 vaccinates after booster vaccination. Although some cellular immune responses were detected after initial or booster vaccination of elk with SRB51 or S19, our data suggest that responses tend to be transient and much less robust than previously reported in SRB51-vaccinated cattle (Bos taurus) or bison (Bison bison). These data may explain why the vaccination of elk with S19 and SRB51 induces poor protection against brucellosis.
[Show abstract][Hide abstract] ABSTRACT: Elk (Cervus claphus) are reservoirs for Brucella abortus, Mycobacterium bovis, and Mycobacterium avium subsp. paratuberculosis, each a serious pathogen of domestic livestock. An understanding of the basic immune responsiveness of elk would aid efforts to develop methods to diagnose and prevent these diseases of elk. Peripheral blood mononuclear cells (PBMC) isolated from captive elk were examined for phenotype, lymphocyte subset proliferative capacity, and ability to produce nitric oxide (NO) upon pokeweed mitogen (PWM) stimulation. Although gamma delta TCR+ cells represented a high percentage of the peripheral blood lymphocyte pool, these cells responded poorly to PWM stimulation. B cells (i.e., sIgM+ cells), conversely, were responsive to PWM stimulation. Addition of PWM to PBMC cultures also resulted in a significant production of nitrite, the stable oxidation product of NO. Similar to other ruminant species, the majority of elk peripheral blood sIgM+ cells co-expressed MHC class II and B-B4, a B cell lineage marker that varies in expression during B cell development. Findings from the present study provide basic information on several parameters of cellular immunity of elk.