LUNG ALLOGRAFT REJECTION IN THE RAT: III. CORRESPONDING MORPHOLOGICAL REJECTION PHASES IN VARIOUS RAT STRAIN COMBINATIONS

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Abstract
Rejection of RT1-incompatible lung grafts results in 4 consecutive morphological rejection phases: the latent, the vascular, the alveolar and the destruction phase. The most prominent signs of rejection occur early in the vascular phase in the bronchus-associated lymphoid tissue (BALT) of these grafts. Whether these 4 phases and the early rejection signs in BALT are universal phenomena of lung allograft rejection was investigated. Various donor-recipient combinations of inbred rat strains, incompatible for the MHC [major histocompatibility complex] or for minor loci, were compared with respect to histological rejection-phenomena, both in the lung graft and in the recipient''s spleen, and alloantibody formation. The 4 rejection phases appeared sequentially in grafts of all combinations. Duration of the phases depended on the degree of histoincompatibility of the graft. BALT was involved early in the rejection process. During the vascular phase a strong immune response developed in the spleen, and in the alveolar phase antibodies circulated in the blood. These morphological rejection phases are universal phenomena of the rejection process against lung allografts in rats. Corresponding phenomena have been described for other species, even in immunosuppressed recipients. A new concept of the universal rejection process of lung allografts is postulated.