Evaluation of innate immune responses in bovine forestomachs

Previous studies had indicated an active role of bovine forestomachs in the response to digestive disorders as well as to inflammatory and infectious processes in the gastro-intestinal (GI) tract and elsewhere. We investigated the potential of bovine forestomachs to receive, amplify and produce mediators of the innate immune response. Indeed, we detected the expression of TIR8 and other receptors and cytokines of the innate immune response, such as Tolllike receptor (TLR)4, interleukin (IL)-1beta, IL-10 and Caspase-1 in the forestomach walls of healthy cows. Their presence suggests an active role of forestomachs in inflammatory disorders of the GI tract and other body compartments. We confirmed and further characterized the presence of leukocytes and cytokines in the rumen fluids. In particular, T and B lymphocytes and myeloid lineage cells were detected in the ruminal content of both rumenfistulated heifers and diseased cows. Also, leukocyte infiltration was modulated by feeding disorders: an acidogenic diet based on daily supplements of maize was shown to inhibit leukocyte accumulation, as opposed to a control, haybased diet, with or without a soy flour (protein) supplement. A survey of 11 dairy farms indicated that low-stress diets and management were correlated with low levels of CD45 gene expression and B cell infiltration in rumen fluids, such as in the “control farm”. In other farms, the rumen fluids of dairy cows showed increased levels of CD45 gene expression and numbers of leukocytes of different lineages (B-cells, T-cells, myeloid cells). This latter pattern of infiltration was correlated with an increased prevalence of inflammatory markers (positive and negative acute phase responses). On the whole, our results indicate that bovine forestomachs can receive and amplify signals for the immune cells infiltrating the rumen content and oral lymphoid tissues. Owing to the above, the examination of the rumen fluid could be a novel and useful diagnostic tool to support the clinical inspections of cattle herds.