Suppressor of cytokine signaling-1 influences bacterial clearance and pathology during the infection with Mycobacterium tuberculosis

Tuberculosis results from an interaction between a chronically persistent pathogen counteracted by IFN-g-mediated immune responses. Modulation of IFN-g signaling could therefore constitute a major immune evasion mechanism for M. tuberculosis. SOCS1 plays a major role in the inhibition of IFN-g-mediated responses. We found that M. tuberculosis infection stimulates SOCS1 expression in mouse and human myeloid cells. Significantly higher levels of SOCS1 were induced after in vitro or in vivo infection with virulent M. tuberculosis-than with attenuated M. bovis BCG. Different innate and adaptive immune mechanisms participated in infection-induced SOCS1 expression. SOCS1 hampered M. tuberculosis clearance both in macrophages and during murine infection in vivo. On the other hand, SOCS1 protected the host from an infection-induced inflammation. Despite SOCS1 expression, mycobacteria-infected macrophages were not tolerant to IFN-g. Instead, an impaired IFN-g secretion by macrophages, associated to lower responses to IL-12, accounted for the increased mycobacterial intracellular growth in presence of SOCS1. SOCS1 attenuated the expression of the majority of genes modulated by infection of macrophages (6,1% of the transcriptome), indicating the relevance of the molecule in the outcome of infection with M. tuberculosis. We suggest that SOCS1 is expressed during M. tuberculosis infection to establish a successful chronic infection, and dampen inflammatory damage. Difference in genotype and TB infection comparison Relative gene expressions were determined by normalized intensity values. GeneSpring analysis was performed using the Treg transcriptome data with following comparisons: no GvHD d90 versus no GvHD d150, no GvHD d90 versus acute GvHD, no GvHD d150 versus chronic GvHD, acute GvHD versus chronic GvHD, acute GvHD versus GvHD d90 and chronic GvHD versus GvHD d150 (Figure 2). Cut-off was a transcript fold change of +2 or -2 in at least one comparison. Student´s t-test was used to identify significant expression changes.