Selective Th2 pattern of cytokine secretion in Mycobacterium avium subsp. paratuberculosis infected Crohn's disease

The pathogenesis of Crohn's disease (CD) remains unclear. A major controversy has been whether infection with Mycobacterium avium subspecies paratuberculosis (MAP) plays a significant role. Current support for a role of MAP is largely based on epidemiological data. The aim of this study was to determine whether MAP detection in gut biopsies is associated with a different cytokine secretion profile as observed in whole blood culture.

A whole blood culture system was employed to measure cytokine secretion, using an ELISA assay, in subjects with CD (n = 46), ulcerative colitis (n = 30), irritable bowel syndrome (n = 22) and normal controls (n = 18). MAP status was defined by nested PCR using an IS900 sequence unique to MAP.

Significantly higher levels of interleukin (IL)-4 (P < 0.05) and IL-2 (P < 0.05) were found in MAP+ CD compared to MAP- CD. This was selective, as MAP+ subjects in both normal and disease controls had similar levels of IL-4 and IL-2 to those with no detectable MAP. IL-4 secretion was correlated with IL-2 production in blood cultures in CD (P < 0.01), consistent with a skewed Th2 immune response.

This data set provides the first evidence of altered T cell function linked to MAP infection in CD, and provides a link between detection of MAP and disease. The pattern of cytokine shift in CD is consistent with the concept that the increasing incidence of CD is in part related to the hygiene theory.