Evidence for the involvement of lung-specific gammadelta T cell subsets in local responses to Streptococcus pneumoniae infection.

Although gammadelta T cells are involved in the response to many pathogens, the dynamics and heterogeneity of the local gammadelta T cell response remains poorly defined. We recently identified gammadelta T cells as regulators of macrophages and dendritic cells during the resolution of Streptococcus pneumoniae-mediated lung inflammation. Here, using PCR, spectratype analysis and flow cytometry, we show that multiple gammadelta T cell subsets, including those bearing Vgamma1, Vgamma4 and Vgamma6 TCR, increase in number in the lungs of infected mice, but not in associated lymphoid tissue. These gammadelta T cells displayed signs of activation, as defined by CD69 and CD25 expression. In vivo BrdU incorporation suggested that local expansion, rather than recruitment, was the principal mechanism underlying this increase in gammadelta T cells. This conclusion was supported by the finding that pulmonary gammadelta T cells, but not alphabeta T cells, isolated from mice that had resolved infection exhibited lung-homing capacity in both naive and infected recipients. Together, these data provide novel insights into the origins of the heterogeneous gammadelta T cell response that accompanies lung infection, and the first evidence that inflammation-associated gammadelta T cells may exhibit distinct tissue-homing potential.