Cytokine secretion by peripheral blood mononuclear cells from cows infected with Mycobacterium paratuberculosis

Objective-To compare cytokine secretion patterns of peripheral blood mononu clear cells (PBMC) from healthy cows and cows subclinically and clinically infected with Mycobacterium paratuberculosis. Animals-5 noninfected cows, 6 cows with subclinical paratuberculosis, and 4 cows with clinical paratuberculosis. Procedure-PBMC were isolated, and con centrations or activities of secreted interleukin (IL)-1, IL-2, IL-6, tumor necrosis factor (TNF), and interferon-gamma (IFN-gamma) were measured afte r in vitro stimulation of cells with concanavalin A (ConA), lipopolysacchar ide (LPS), or a whole-cell sonicate of M paratuberculosis (MpS). Proliferat ive responses of PBMC were also determined after stimulation with ConA, phy to-hemagglutinin, pokeweed mitogen (PWM), or MpS. Results-After stimulation with ConA, cells from subclinically infected cows secreted significantly more, and cells from clinically infected cows secre ted significantly less, IFN-gamma, compared with cells from control cows. C ells from cows with subclinical paratuberculosis produced significantly mor e TNF and IFN-gamma in response to MpS than cells from the other 2 groups. Stimulation of PBMC from subclinically infected cows with ConA or MpS resul ted in significantly higher proliferative responses, compared with cells fr om control and clinically infected cows. In contrast, clinically infected c ows had significantly higher proliferative responses to PWM than cells from the other 2 groups. Conclusions and Clinical Relevance-A decrease in T-cell responses to mitoge ns or MpS was observed in cows clinically infected with M paratuberculosis, compared with subclinically infected cows, suggesting that activated T cel ls may delay the progression of paratuberculosis.