Clinical Disease Upregulates Expression of CD40 and CD40 Ligand on Peripheral Blood Mononuclear Cells from Cattle Naturally Infected with Mycobacterium avium subsp paratuberculosis

CD40 and CD40 ligand (CD40L) have costimulatory effects as part of a complex series of events in host immunity. In this study, the expression of CD40 and CD40L on peripheral blood mononuclear cells (PBMCs) isolated from cattle with Johne's disease were measured on freshly isolated PBMCs and on cells cultured for 8, 24, and 72 h in the presence or absence of live Mycobacterium avium subsp. paratuberculosis and exogenous gamma interferon, interleukin 10, and transforming growth factor beta. Results demonstrated greater CD40 and CD40L expression on fresh PBMCs obtained from animals in the clinical stage of disease (symptomatic) than those from healthy control animals or cows in the subclinical stage of disease (asymptomatic). A similar expression profile with greater magnitude was noted for cultured PBMCs, with increased CD40 expression after 8 and 24 h of culture and increased CD40L expression between 24 and 72 h on PBMCs obtained from clinically infected animals. The addition of live M. avium subsp. paratuberculosis to cell cultures resulted in downregulation of CD40L expression in naturally infected cows, regardless of the disease stage. In contrast, the addition of live M. avium subsp. paratuberculosis to cultures resulted in upregulation of CD40 expression on cells obtained from clinically infected animals, while a decrease in expression was noted for healthy and subclinically infected cows. No effects of exogenous cytokines on CD40 or CD40L expression were observed. These results clearly point for the first time to a disparity in the expression of these costimulatory molecules on immune cells from cattle in different stages of Johne's disease and suggest further investigation into their roles in paratuberculosis pathogenesis.