Diets containing different fermentable substrates can affect mucosal and systemic immune parameters in rats under homeostatic conditions

•Immune effects varied with diet and tissue examined.•A wheat bran-containing diet increased levels of IL-10 in the ileum of male rats and spleen of female rats.•Diets containing oat bran or resistant starch induced pro-inflammatory cytokine profiles in the colon and MLN, respectively.•Oat bran and resistant starch heightened levels of the regulatory cytokine TGF-β1 in the liver under resting conditions.