1. ¹Immunology Group, International Centre for Genetic Engineering and Biotechnology, New Delhi, India
2. ²Structural Biology Laboratory, National Institute of Immunology, New Delhi, India

Correspondence: Dr Pawan Sharma, Immunology Group, International Centre for Genetic Engineering and Biotechnology (ICGEB), Aruna Asaf Ali Marg, PO Box-10504, New Delhi 110067, India. E-mail: pawan37@gmail.com

Received 1 June 2007; Revised 21 July 2007; Accepted 16 August 2007; Published online 2 October 2007.

Abstract

Mycobacterium tuberculosis (Mtb) causes death of 2–3 million people annually and is considered one of the most successful intracellular pathogens to persist inside the host macrophage. Recent studies have implicated the role of RD-1 region of Mtb genome in the mycobacterial pathogenesis. The role of RD-1-encoded secretory proteins of Mtb in modulation of macrophage function has not been investigated in detail. Here we show that RD-1 encoded two major secretory proteins, namely, culture filtrate protein-10 kDa (CFP-10) and early secreted antigenic target-6 kDa (ESAT-6), and their 1:1 CFP-10:ESAT6 complex inhibit production of reactive oxidative species (ROS) in RAW264.7 cells. These proteins also downregulated the bacterial lipopolysaccharide (LPS)-induced ROS production, which, in turn, downregulated LPS-induced nuclear factor-B (NF-B) p65 DNA-binding activity, as well as inhibited the NF-B-dependent reporter gene (chloramphenicol acetyl transferase) expression in the treated macrophages. Moreover, addition of N-acetyl cysteine, which is a scavenger of ROS, also inhibited LPS-induced reporter gene expression by scavenging the ROS, thereby preventing NF-B transactivation. These studies indicate that the secretory proteins CFP-10, ESAT-6 and the CFP10:ESAT6 complex of Mtb can inhibit LPS-induced NF-B-dependent gene expression via downregulation of ROS production.