CELLULAR ACTIVATION IN DIFFERENT STAGES OF INFECTION WITH MYCOBACTERIUM AVIUM SUBSP. PARATUBERCULOSIS IN CATTLE
Location: Infectious Bacterial Diseases Research Unit
Title: Osteopontin: A Novel Cytokine Involved in the Regulation of Mycobacterium avium subsp. paratuberculosis Infection in Periparturient Dairy Cattle
Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 6, 2008
Publication Date: August 1, 2008
Citation: Karcher, E.L., Bayles, D.O., Bannantine, J.P., Beitz, D.C., Stabel, J.R. 2008. Osteopontin: A Novel Cytokine Involved in the Regulation of Mycobacterium avium subsp. paratuberculosis Infection in Periparturient Dairy Cattle. Journal of Dairy Science. 91(8):3079-3091.
Johne's disease is a chronic, debilitating intestinal disorder in cattle characterized by diarrhea, reduced feed intake, weight loss and death. Cattle usually become infected as young calves by ingesting feces containing the causative bacteria. However, symptoms of disease do not usually present themselves until the animals reach 3 to 5 years of age or even older. Clinical signs of disease may be precipitated by stressors such as parturition, heavy lactation, concomitant viral or bacterial infections, and malnutrition. It is well known that parturition causes cows to become immunosuppressed and makes them more susceptible to infections such as mastitis and metritis as well as other viral and bacterial pathogens. The present study was designed to evaluate the effects of the periparturient period on the expression and secretion of a novel protein, osteopontin, involved in host immunity to mycobacteria. Parturition decreased host immunity in cows regardless of infection status. In addition, paratuberculosis resulted in changes in expression of this protein compared to healthy noninfected cows. These results suggest that the periparturient period is a highly significant period for the dairy cow and may result in increased susceptibility to infectious diseases due to changes in host immunity.
Osteopontin (Opn), an important mediator of the cell-mediated immune response, enhances the host immune response against mycobacterial infections. Infections caused by the intracellular bacterium, Mycobacterium avium subsp. paratuberculosis (MAP), have a devastating impact on the dairy industry. We sought to characterize Opn at both the level of gene and protein expression in periparturient dairy cows naturally infected with MAP. Peripheral blood mononuclear cells (PBMCs) were isolated from control, subclinical, and clinical periparturient dairy cows naturally infected with MAP beginning 3 wks pre- to 5 wks post-calving and incubated with medium alone (nonstimulated: NS), concanavalin A (ConA) or a whole-cell sonicate of MAP (MPS). Real-time PCR was performed to evaluate expression of Opn and classical Th1 and Th2 cytokines. Results demonstrated greater Opn expression in nonstimulated PBMCs isolated from subclinical cows compared with control and clinical cows. For clinical cows, there was a strong correlation between Opn expression and expression of the Th1 cytokines, IFN-gamma and IL-1alpha for nonstimulated PBMCs, and IFN-gamma and IL-12 for PBMCs stimulated with MPS. Expression of TNF-alpha was greater in clinical cows than the other groups. In support of a Th1/Th2 dichotomy, nonstimulated (NS), ConA, and MPS-stimulated PBMCs from subclinical cows secreted more IFN-gamma, and MPS-stimulated PBMCs from clinical cows secreted more IL-4 compared with the other groups. Immunoblot analysis of PBMCs detected four Opn proteins at 60, 52, 34, and 27 kDa. There was an interaction of infection group and parturition with increased Opn protein in PBMC lysates at calving for both subclinical and control cows. This is the first study to evaluate the role of Opn on the immune response of dairy cows naturally infected with MAP. Results of this study suggest Opn may be a key regulator against MAP infection.