Intragraft proliferating T lymphocytes are associated with moderate acute pulmonary rejection

Acute allograft rejection is characterized by infiltration of the donor org an by host lymphoid cells, predominantly T lymphocytes, However, the site o f proliferation and clonal expansion of alloreactive T lymphocytes is not w ell defined in man. A group of normal transbronchial biopsies (TBB, n=9) fr om clinically well lung transplant recipients was compared to TBB showing a cute rejection (at least grade A2, n=9), using CD3- and Ki67-specific antib odies to double-label proliferating T lymphocytes. Few double-labeled lymph ocytes were present in the normal biopsies (range, 0-3 cells). However, fiv e of the rejection biopsies contained significant numbers of proliferating T lymphocytes (range, 19-47; Fisher's exact test; P=0.029), Furthermore, th is positive group contained all three cases of grade A3 rejection in the st udy, as well as a case with persistent grade A2 rejection on follow-up biop sy, These data demonstrate that T lymphocytes do proliferate in transplante d human lungs; such proliferation is associated with more severe rejection.