Mycobacterium tuberculosis (MTB) infection induces a strong immune response, but by an as yet unknown mechanism, can persist within macrophages. In July Journal of Immunology Erika Noss and colleagues from Case Western Reserve University, Cleveland, Ohio show that a 19-kDa lipoprotein produced by MTB, inhibits antigen processing by macrophages and prevents recognition by T cells, thereby promoting chronic TB infection.

Using electroelution techniques, Noss et al. extracted a specific component from an MTB Triton X-114 lysate which they identified with Abs to be MTB 19-kDa lipoprotein. This lipoprotein inhibited macrophage expression of class II MHC (MHC-II) molecules and MHC-II Ag processing of both soluble Ags and Ag 85B from intact MTB bacilli. The inhibition of MHC-II Ag processing induced by MTB 19-kDa lipoprotein was dependent on macrophage Toll-like receptor (TLR) 2, which normally enables the cell to recognize invading pathogens (J Immunol 2001, 167:910-918).

These results suggest...