Acute rejection of experimental lung allografts: Characterization of intravascular mononuclear leukocytes

Leukocytes interacting with endothelia of lung allografts probably play a seminal role in acute rejection, but have not been characterized before. Transplantation was performed in the Lewis to Lewis and in the Dark Agouti to Lewis rat strain combinations. DNA replication was detected in T-cells on day 2 after pulse-labelling in vivo with 5-bromo-2′-deoxyuridine (BrdU). On day 5, leukocytes were isolated by intensive perfusion the graft, subject to flow cytometry and to quantitative RT–PCR. About 34 million leukocytes accumulated in allograft vessels, but only 10 and 6 million cells in isografts and control lungs, respectively. During rejection, IFN-γ, IL-1β and IL-10 mRNA expression increased, IL-12 mRNA decreased, whereas IL-2, IL-6, TNF-α, and TGF-β mRNA did not change. The phenotype of graft monocytes was partially activated and intravascular T-cells proliferated. In conclusion, during rejection, monocytes with unusual properties accumulate and T-lymphocytes are activated in lung allograft blood vessels.