Mycobacterium avium subspecies induce differential expression of pro-inflammatory mediators in a murine macrophage model: evidence for enhanced pathogenicity of Mycobacterium avium subspecies paratuberculosis.

Mycobacterium avium subspecies (ssp.) paratuberculosis (MAP) is the etiological agent of paratuberculosis, a chronic, non-treatable granulomatous enteritis of ruminants. MAP is the only mycobacterium affecting the intestinal tract, which is of interest since it is presently the most favoured pathogen linked to Crohn's disease (CD) in humans due to its frequent detection in CD tissues. MAP is genetically closely related to other M. avium ssp. such as M. avium ssp. avium (MAA) and M. avium ssp. hominissuis (MAH) which can cause mycobacteriosis in animals and immunocompromised humans. We have recently shown that murine macrophage cell lines represent suitable systems to analyse M. avium ssp. patho-mechanisms and could show that MAP, but not MAA, specifically inhibited the antigen-specific stimulatory capacity for CD4(+) T-cells. In the present study, we compared gene expression profiles of murine RAW264.7 macrophages in response to infections with MAP or MAA using murine high-density oligonucleotide Affymetrix microarrays. A comparison of MAP and MAA infection revealed 17 differentially expressed genes. They were expressed at a much lower level in MAP-infected macrophages than in MAA-infected macrophages. Among these were the genes for IL-1beta, IL-1alpha, CXCL2, PTGS2 (COX2), lipocalin (LCN2) and TNF, which are important pro-inflammatory factors. The microarray data were confirmed for selected genes by quantitative real-time reverse transcription PCR and, by protein array analyses and ELISA. Similar to MAA, infection with MAH also showed robust induction of IL-1beta, CXCL2, COX2, LCN2 and TNF. Taken together, our results from M. avium ssp.-infected murine macrophages provide evidence that MAP in contrast to MAA and MAH specifically suppresses the pro-inflammatory defence mechanisms of infected macrophages.