The lung contains large numbers of preformed IL-17A secreting recipient γδ T cells. (A) G-CSF mobilized BALB/c.WT (CD45.1⁺) grafts were transplanted into lethally irradiated (CD45.2⁺) B6.WT and B6.IFN-γR^−/− recipients (n = 8 to 10 per group combined from 2 experiments). Lung tissue was harvested and cells were sort purified based on donor hematopoietic (CD45.1⁺) or recipient hematopoietic (CD45.2⁺) congenic markers at day 5 post-SCT. IL-17A expression was analyzed by qRT-PCR and normalized to β2M. ****P < .0001; **P < .01. (B) G-CSF mobilized BALB/c.WT (CD45.1⁺) grafts were transplanted into B6.IL-17-eYFP fate map reporter recipients (n = 3 per group) and flow cytometry undertaken on lung cells before and after alloSCT. Representative plots demonstrating that 1% to 2% of lung cells report for IL-17A even prior to alloSCT (top panel) and that these cells are predominantly (72% to 86%) γδTCR⁺ T cells (middle panel). The majority of all γδTCR⁺ T cells (63% to 76%) report for IL-17A, even prior to alloSCT (bottom panel). (C) The recipient IL-17A reporter⁺ γδTCR⁺ T cells persist in the lung for at least 5 days after SCT. (D) Representative plots of recipient T cells in the lungs of B6.WT or B6.IFN-γR^−/− recipients 3 days after alloSCT, and (E) total numbers (n = 5 per group), *P < .01.