IL-6 is generated by recipient lung epithelium and endothelium. G-CSF mobilized BALB/c.WT grafts were transplanted into lethally irradiated B6.WT and B6.IFN-γR^−/− recipients (n = 5 to 12 per group combined from 2 experiments). Sera were obtained on days 1 to 5 and soluble protein extracts were prepared from homogenized lung, liver, and GI tract tissue harvested on day 5 post-SCT. (A) Serum IL-6 levels. (B) IL-6 and TNF levels measured in soluble protein extracts from lung, liver, and GI tract tissue. ****P < .0001; ***P < .001; **P < .01. (C) IL-17A, G-CSF, and GM-CSF levels measured in soluble protein extracts from lung tissue on day 5. ***P = .0008; G-CSF, **P = .002; *P = .011. (D) Lung tissue was harvested from B6.WT and B6.IFN-γR^−/− recipients (n = 4 to 10 combined from 2 replicate experiments) of G-CSF mobilized BALB/c CD45.1⁺ grafts and cells were sort purified based on donor hematopoietic (CD45.1⁺), recipient hematopoietic (CD45.2⁺), or recipient nonhematopoietic (CD45.1^negCD45.2^neg) congenic markers at day 5 post-SCT. Cytokine expression was analyzed by real time quantitative reverse transcription PCR (qRT-PCR) for IL-6, TGFβ, and IL-21 transcripts. mRNA expression was determined relative to the expression of the housekeeping gene, β2M. IL-6: ***P = .0006, host hematopoietic WT vs IFN-γR^−/−; ****P < .0001, host nonhematopoietic WT vs IFN-γR^−/−; *P = .03, host hematopoietic IFN-γR^−/− vs host nonhematopoietic IFN-γR^−/−; IL-21: *P = .02, donor hematopoietic WT vs IFN-γR^−/−; **P = .001, host nonhematopoietic WT vs IFN-γR^−/−; TGFβ: **P = .003, host hematopoietic WT vs IFN-γR^−/−; ****P < .0001, host nonhematopoietic WT vs IFN-γR^−/−. (E) IL-6 mRNA expression quantified in sort purified pulmonary endothelial cells (CD45^negCD31⁺) and epithelial cells (CD45^negCD326⁺) from lung tissue harvested at day 5 post-SCT (n = 5 to 9 per group combined from 2 replicate experiments). **P = .007, epithelial cells, WT vs IFN-γR^−/− recipients.