Serum IgG Immunoglobulin Levels are Associated with Reduced PCR Detection of Mycoplasma bovis in Naturally Infected...

Mycoplasma bovis (M. bovis) is an important pathogen of American bison (Bison bison), associated with high morbidity and mortality epizootics of respiratory and reproductive disease. Despite the significant negative impact on bison health, little is known about the kinetics of disease and the host immune response to infection. To address these questions, a cohort of bison calves was created and serially sampled 5 times, once every 2-3 mo, over a 12-mo period. At each sampling period nasal swab samples were collected and tested by PCR for the presence of M. bovis. Serum samples were also collected and assessed for M. bovis-specific antibodies using both a commercial and an in-house ELISA. Overall, 19/41 bison (46.3%) had positive PCR tests, and 31/41 (75.6%) were seropositive. Over the course of the study, the frequency of PCR-positive nasal swabs and the ELISA scores decreased, although serum samples remained positive for at least 6 mo following the final positive PCR test. Bison were grouped according to results from the in-house ELISA into high-responder (n=7), low-responder (n=5), and seronegative (n=7) groups. M. bovis-specific IgG antibody levels were significantly elevated in the high-responder group compared to the low-responder and seronegative groups. The differences were statistically significant for 3/5 sampling periods. A trend toward increased IgG2 levels was observed in the high-responder group. High total IgG responses correlated with a decline in positive PCR tests from nasal swabs. These data provide evidence that a strong humoral response is beneficial and is probably involved in the clearance of M. bovis from bison.