Vγ2Vδ2 cells, a class of T cells found only in primates, are reactive to nonpeptide organophosphate and alkylamine antigens secreted by bacteria and parasites. These cells make up 2-5% percent of human peripheral blood T cells but expand to make up 8–60% of peripheral blood T cells during bacterial and parasitic infections. We show here, using a chimeric severe combined immunodeficiency (SCID) mouse (hu-SCID) model, that human Vγ2Vδ2 T cells mediate resistance to extracellular gram-positive (Staphylococcus aureus) and gram-negative (Escherichia coli and Morganella morganii) bacteria, as assessed by survival, body weight, bacterial loads, and histopathology. Surprisingly, this bacterial resistance was evident 1 day after infection, and bacteria were cleared well before γδ T cell expansion was detected 6 days after infection. Decreased resistance in Vδ2 T cell–depleted hu-SCID mice correlated with decreased serum IFN-γ titers. Intravenous treatment of infected, reconstituted hu-SCID mice with pamidronate, a human Vγ2Vδ2 T cell–specific aminobisphosphonate antigen, markedly increased the in vivo antibacterial effect of Vγ2Vδ2 T cells. Therefore, this large pool of antigen-specific, yet immediately reactive memory human Vγ2Vδ2 T cells is likely to be an important mediator of resistance against extracellular bacterial infection and may bridge the gap between innate and acquired immunity.
Lisheng Wang, Arati Kamath, Hiranmoy Das, Lin Li, Jack F. Bukowski