The Glycosylated Rv1860 Protein of Mycobacterium tuberculosis Inhibits Dendritic Cell Mediated TH1 and TH17 Polarization of T Cells and Abrogates Protective Immunity Conferred by BCG

We previously reported interferon gamma secretion by human cd4+ and cd8+ t cells in response to recombinant e. coli-expressed rv1860 protein of mycobacterium tuberculosis (mtb) as well as protection of guinea pigs against a challenge with virulent mtb following prime-boost immunization with dna vaccine and poxvirus expressing rv1860. in contrast,a statens serum institute mycobacterium bovis bcg (bcg-ssi) recombinant expressing mtb rv1860 (bcg-tb1860) showed loss of protective ability compared to the parent bcg strain expressing the control gfp protein (bcg-gfp). since rv1860 is a secreted mannosylated protein of mtb and bcg,we investigated the effect of bcg-tb1860 on innate immunity. relative to bcg-gfp,bcg-tb1860 effected a significant near total reduction both in secretion of cytokines il-2,il-12p40,il-12p70,tnf-α,il-6 and il-10,and up regulation of co-stimulatory molecules mhc-ii,cd40,cd54,cd80 and cd86 by infected bone marrow derived dendritic cells (bmdc),while leaving secreted levels of tgf-β unchanged. these effects were mimicked by bcg-tb1860his which carried a 6-histidine tag at the c-terminus of rv1860,killed sonicated preparations of bcg-tb1860 and purified h37rv-derived rv1860 glycoprotein added to bcg-gfp,but not by e. coli-expressed recombinant rv1860. most importantly,bmdc exposed to bcg-tb1860 failed to polarize allogeneic as well as syngeneic t cells to secrete ifn-γ and il-17 relative to bcg-gfp. splenocytes from mice infected with bcg-ssi showed significantly less proliferation and secretion of il-2,ifn-γ and il-17,but secreted higher levels of il-10 in response to in vitro restimulation with bcg-tb1860 compared to bcg-gfp. spleens from mice infected with bcg-tb1860 also harboured significantly fewer dc expressing mhc-ii,il-12,il-2 and tnf-α compared to mice infected with bcg-gfp. glycoproteins of mtb,through their deleterious effects on dc may thus contribute to suppress the generation of a th1- and th17-dominated adaptive immune response that is vital for protection against tuberculosis. © 2014 satchidanandam et al.