SOCS1 gene expression is increased in severe pulmonary tuberculosis.

Suppressors of cytokine signalling (SOCS) molecules inhibit cytokine signalling and may regulate protective immunity in tuberculosis (TB). We investigated the association of SOCS with disease progression in patients with pulmonary TB. For this purpose, we studied peripheral blood mononuclear cells (PBMCs) and T cells from patients with pulmonary TB (TB, n=33) and healthy endemic controls (EC, n=15). Cases were stratified into those with moderately advanced (Mod-PTB) or far advanced disease (Adv-PTB). Interferon-gamma (IFN-γ), SOCS1 and SOCS3 gene expression was determined by RT-PCR. Statistical analysis was performed using the Mann-Whitney test. Levels of IL6 (P=0.018) and IL10 (P=0.013) were found to be elevated in PBMC supernatants from patients with TB as compared with EC. SOCS1 mRNA gene expression in T cells from patients with TB was increased as compared with that of EC (P=0.02). In addition, levels of SOCS1 mRNA transcripts were found to be elevated in PBMCs of Adv-PTB as compared with Mod-PTB (P=0.008) cases. Our data show that raised SOCS1 levels are associated with increased disease severity in TB. As SOCS1 regulates IFN-γ-driven immunity and SOCS1 can be further upregulated by IL6 levels, the increase in SOCS1 in severe disease indicates a mechanism by which mycobacteria impede disease control in TB.