Immune responses of elk to Mycobacterium bovis bacillus Calmette Guerin vaccination

Although rare, detection of Mycobacterium bovis infection of captive or free-ranging elk (Cervus elaphus) elicits serious concern due to regulatory and zoonotic implications. Few studies, however, have evaluated the immune response of elk to M. bovis or other pathogens. To model natural infection, elk were vaccinated with live M. bovis bacillus Calmette Guerin (BCG, Pasteur strain) for evaluation of immune responsiveness to this attenuated live vaccine. Peripheral blood mononuclear cells (PBMC) of vaccinated elk proliferated in response to stimulation with a soluble mycobacterial antigen preparation (i.e. M. bovis purified protein derivative, PPDb). Greater numbers of sIgM(+) cells (i.e. B cells) proliferated in this response than did either CD4(+), gammadeltaTCR(+) or CD8(+) cells. The in vivo response (i.e. delayed type hypersensitivity, DTH) to PPDb by vaccinated elk exceeded both the response by non-vaccinated elk and BCG-vaccinated cattle at 24, 48, and 72h post-administration of PPD. In vivo responses to PPDb by vaccinated elk diminished after 72h as compared to responses at 24 and 48h. Serum was also collected periodically and evaluated by ELISA for immunoglobulin (i.e. IgG heavy and light chains) reactivity to crude mycobacterial antigens. Two weeks post-vaccination and throughout the duration of the study, serum immunoglobulin reactivity to PPDb and to a proteinase K-digested whole cell sonicate of BCG exceeded that of serum from non-vaccinated elk. Intradermal administration of PPD for measurement of hypersensitive responses boosted the serum antibody response. These findings demonstrate that BCG vaccination of elk induces a serum antibody response to crude M. bovis antigens, a B cell in vitro proliferative response, and in vivo trafficking of mononuclear cells to sites of mycobacterial antigen administration (i.e. delayed type hypersensitivity). A predominant B cell in vitro proliferative response by elk PBMC to crude mycobacterial test antigens will likely impact the development of improved diagnostic tests of tuberculosis infection for this species.