Protective effect of PN-1 from BM cells in bleomycin-injured chimeric mice.PN-1^−/− mice and their PN-1^+/+ littermates were irradiated and underwent transplantation with BM from appropriated mice and allowed to recover for 5 weeks before bleomycin-induced lung injury. PN-1^+/+ BM → PN-1^+/+: PN-1^+/+ mice receiving PN-1^+/+ BM transplants (n = 10). PN-1^−/− BM → PN-1^+/+: PN-1^+/+ mice receiving PN-1^−/− BM transplants (n = 8). PN-1^+/+ BM → PN-1^−/−: PN-1^−/− mice receiving PN-1^+/+ BM transplants (n = 7). PN-1^−/− BM → PN-1^−/−: PN-1^−/− mice receiving PN-1^−/− BM transplants (n = 5). (A) Percentages of surviving mice undergoing transplantation were plotted over a 14-day period after bleomycin treatment. Log-rank test was used to compare the difference between similar recipient mice. P = .03 for PN-1^+/+ BM → PN-1^−/− vs PN-1^−/− BM → PN-1^−/−, and P = .002 for PN-1^+/+ BM → PN-1^+/+ vs PN-1^−/− BM → PN-1^+/+. (B) Masson’s trichrome and Sirius red stainings of lung withdrawn the day of euthanasia from PN-1^+/+ and PN-1^−/− chimeric mice. Representative images are shown. Scale bars, 100 µm.