Significance Bacteria stimulate host cells in part via secreted products, some of which are packaged in membrane vesicles (MV). MV released by the major human pathogen Mycobacterium tuberculosis (Mtb) carry lipoprotein LpqH, a major agonist for host Toll-like receptor 2 (TLR2). This study identifies a gene, rv0431 , which appears to regulate mycobacterial MV formation, and therefore we suggest it be named “vesiculogenesis and immune response regulator” ( virR ). This gene encodes a protein that includes a unique fold, as determined by NMR spectroscopy, and a disordered domain suggestive of participation in a higher-order complex. By restraining the release of most of the material released by Mtb that activates host cells through TLR2, VirR reduces Mtb’s immunostimulatory potential and increases its virulence.