THE LUNG AS A SOURCE AND A TARGET ORGAN FOR T-LYMPHOCYTE AND B-LYMPHOCYTE

In lung transplantation, a substantial number of donor leukocytes are transferred from the donor to the recipient by the graft. Using a rat model, it was analyzed in this study to what extent leukocytes leave t he lung, to which phenotype they belong, and to which organs they migr ate. The model used was the orthotopic transplantation of the left lun g of LEW.7B(RT7(b)) rats into LEW(RT7(a)) recipients. Lung allografts are not rejected in this strain combination, which differs only in the RT7 system, a genetic polymorphism of CD45. Using the RT7(b) marker ( monoclonal antibody His41), the distribution of donor leukocytes passi vely transferred with the graft was studied by immunohistology 2 wk af ter transplantation. At this time, 2.9 +/- 0.1% (n = 6) of the periphe ral blood leukocytes in the recipients were derived from the donor lun g. The donor cell population detected in the blood consisted of T cell s (59 +/- 4%), B cells (5.1 +/- 0.2%) and a surprisingly high fraction of natural killer (NK) cells (36 + 3%). No monocytes or granulocytes were found. In lymph nodes, spleen and thymus donor-derived T-and B-ce lls could be shown in typical T-and B-areas, respectively. Donor-deriv ed leukocytes were found in the liver and the skin. In the tissue and the bronchoalveolar lavage (BAL) of the host lung, predominantly T cel ls were found. Furthermore, in the donor tissue and BAL more than 70% of T- and B-cells were host type, demonstrating that the donor lung ha d been repopulated to a great extent by host lymphocytes. This support s the relevance of BAL as a diagnostic tool in lung diseases. Thus, th e lung is an immunologically important site, releasing lymphocytes whi ch migrate to other organs and also attracting many lymphocytes from t he circulation.