Rv3615c is a highly immunodominant antigen and specifically induces potent Th1-type immune responses in tuberculosis pleurisy.

T-cell responses have been demonstrated to be essential for preventing infection. The Th1-cytokines produced by T cells, such as INF-γ, IL-2, and TNF-α, not only limit the invasion of but also eliminate the pathogen at the site of infection. Bacillus Calmette-Guérin (BCG) is known to induce Th1-type responses but the protection is inadequate. Identification of immunogenic components, in addition to those expressed in BCG, and induction of a broad spectrum of Th1-type responses provide options for generating sufficient adaptive immunity. Here, we studied human pulmonary T-cell responses induced by the -specific antigen Rv3615c, a protein with a similar size and sequence homology to ESAT-6 and CFP-10, which induced dominant CD4 T-cell responses in human tuberculosis (TB) models. We characterized T-cell responses including cytokine profiling, kinetics of activation, expansion, differentiation, TCR usage, and signaling of activation induced by Rv3615c compared with other -specific antigens. The expanded CD4 T cells induced by Rv3615c predominately produced Th1, but less Th2 and Th17, cytokines and displayed effector/memory phenotypes (CD45ROCD27CD127CCR7). The magnitude of expansion and cytokine production was comparable to those induced by well-characterized the 6 kDa early secreted antigenic target (ESAT-6), the 10 kDa culture filtrate protein (CFP-10) and BCG. Rv3615c contained multiple epitopes Rv3615c, Rv3615c, Rv3615c, Rv3615c and Rv3615c that activated CD4 T cells. The Rv3615c-specific CD4 T cells shared biased of T-cell receptor variable region of β chain (TCR Vβ) 1, 2, 4, 5.1, 7.1, 7.2 and/or 22 chains to promote their differentiation and proliferation respectively, by triggering a signaling cascade. Our data suggest that Rv3615c is a major target of Th1-type responses and can be a highly immunodominant antigen specific for infection.