Accumulation of gamma/delta T cells in the lungs and their roles in neutrophil-mediated host defense against pneumococcal infection

The present study was designed to elucidate the role of Vγ4+ γδ T cells, a major subset of pulmonary γδ T cells, in host defense against infection with Streptococcus pneumoniae. The proportion and number of whole γδ T cells, identified as CD3+ and TCR-δ+ cells, and Vγ4+ γδ T cells, identified as CD3+ and TCR-Vγ4+ cells, increased in the lungs at 3, 6 and 12 h post-infection. Survival of infected mice and lung bacterial clearance were severely impaired in TCR-Vγ4−/− mice compared with control wild-type (WT) mice. The impaired host protection in TCR-Vγ4−/− mice correlated well with attenuated recruitment of neutrophils in lungs. MIP-2 and TNF-α synthesis in the infected tissues was significantly reduced in TCR-Vγ4−/− mice compared with WT mice. Similar results were noted in the synthesis of TNF-α, but not clearly of MIP-2, by lung leukocytes stimulated with live bacteria. Our results demonstrate that Vγ4+ γδ T cells play an important role in the neutrophil-mediated host defense against S. pneumoniae infection by promoting the synthesis of TNF-α and possibly of MIP-2 in the lungs.