c Antigen-specific ␥␦ T cells may play an important role in the immune response to Mycobacterium tuberculosis. However, little is known about the characteristics of the length distribution of the ␦2-chain complementarity determining region 3 (␦2 CDR3) of the ␥␦ T-cell receptor (TCR) in patients with active pulmonary tuberculosis (TB) on a large scale. In addition, M. tuberculosisactivated ␥␦ T cells potentially inhibit intracellular mycobacterial growth, but phosphoantigen-activated ␥␦ T cells do not. Only a few M. tuberculosis-related antigen peptides or proteins that are recognized by ␥␦ TCR have been identified. Twenty-four healthy donors (HDs) and 27 TB patients were included in the present study. The gene-scanning technique found that the ␦2 CDR3 length distribution patterns of ␥␦ TCR in TB patients were perturbed, and each pattern included different predominant CDR3 sequences. The predominant ␦2 CDR3 sequences of ␥␦ TCRs, which originated from TB patients and HD ␥␦ T cells that were stimulated by M. tuberculosis heat resistance antigen (Mtb-HAg), were used as probes to screen peptides recognized by ␥␦ TCR using a phage display library. We identified four peptides that bound to the predominant ␦2 CDR3 fragments and showed homology to M. tuberculosis genes in a BLAST search. Notably, one peptide was related to M. tuberculosis H37Rv (QHIPKPP), and this fragment was confirmed as a ligand for the ␥␦ TCR. Two fragments, Ag1 and Ag2, activated ␥␦ T cells from HD or TB patients. In summary, the ␦2 CDR3 lineage of TB patients apparently drifts, and the predominant ␦2 CDR3 sequence that recognizes M. tuberculosis may exhibit specificity. The identified M. tuberculosis-related antigen peptides may be used as vaccines or adjuvants for protective immunity against M. tuberculosis.
Mycobacterium tuberculosis causes tuberculosis (TB), which is one of the most common serious chronic infectious diseases. TB is a threat to human health, especially with the increasing human immunodeficiency virus (HIV) pandemic and multidrugresistant strains of M. tuberculosis (1). An estimated 8.6 million people developed TB in 2012, and 1.3 million people died from the disease, including 320,000 deaths in people infected with HIV (2). Different pathways and cell types interact to mediate the innate and adaptive immunities against M. tuberculosis (3). The ␥␦ T-cell subset V␥9V␦2 cells was shown to play an important role in host immunity against M. tuberculosis in many studies (4-6). ␥␦ T cells generally recognize antigens in a non-major histocompatibility complex (MHC)-restricted manner, which is similar to how B cells directly recognize a ligand or antigen. The human ␦ chain is composed of eight V␦ gene fragments, two D␦ gene fragments, three J␦ gene fragments, and one C␦ gene fragment, and these fragments are located on the long arm of the 14th chromosome (7). Varying numbers of nucleotides (3 to 24) randomly insert into the connection area of the rearranged T-cell receptor (TCR) V␦ and form a VNDNJ sequence with a highly variable compleme...