Oral, but not intravenous, alloantigen prevents accelerated allograft rejection by selective intragraft Th2 cell activation.

We studied the mechanisms by which oral or intravenous administration of allogeneic splenocytes prevents sensitization by skin allografts and development of accelerated rejection of subsequent cardiac allografts. LEW rats were sensitized with BN skin allografts 7 days prior to receiving heterotopic (LEW x BN)F1 vascularized cardiac allografts. While unsensitized cardiac allografts are rejected on days 6-8, control sensitized grafts were rejected within 24 to 48 hr. Oral administration of BN splenocytes during the sensitization phase (between skin and heart grafting) has been found to prevent accelerated allograft rejection and prolong cardiac allograft survival to 7 days. An alternative route of antigen exposure, specifically intravenous administration of BN splenocytes (50 x 10(6) daily for 5 days starting on the day of skin grafting), also prevented accelerated cardiac allograft rejection and prolonged allograft survival to 9 +/- 1 days (n = 5). Immunoperoxidase studies of cardiac allografts harvested 24-48 hr posttransplant showed that, when compared with sensitized controls, animals that received oral splenocytes had reduced deposition of IgG (end-point titer of 1/1000 vs. 1/4000), IgM (1/1000 vs. 1/16000), C3 (1/4000 vs. 1/16000), and fibrin (1/4000 vs. 1/16000). There was also decreased infiltration by macrophages (18 +/- 8 vs. 37 +/- 8 cells/HPF, P < 0.01), T cells (5 +/- 3 vs. 19 +/- 7, P < 0.01), and IL-2R+ T cells (5 +/- 3 vs. 15 +/- 4, P < 0.01), and a significant reduction in the numbers and extent of intragraft mononuclear cells stained with antibodies to IL-1, IL-2, IL-6, IL-8, IFN-gamma, and TNF-alpha. In contrast, these grafts showed markedly increased IL-4 staining (including most mononuclear and all endothelial cells), as compared with control grafts (< 20% of mononuclear cells and only focal endothelial staining). Immunoperoxidase studies of cardiac allografts harvested from rats receiving intravenous splenocytes also showed markedly reduced humoral deposits and cellular infiltrates, comparable to that found in the oral splenocytes-treated group, but showed significantly different cytokine expression. In particular, some intragraft mononuclear cell labeling for IFN-gamma remained, and IL-4 staining was not increased relative to control grafts. Attempts were then made to abrogate spleen cell-induced prolongation of cardiac allograft survival by daily injections of CD4 monoclonal antibody (BWH-4 mAb, 700 micrograms) from the time of cardiac transplantation, therapy previously shown unable to prolong cardiac survival in this model when commenced after skin graft-induced sensitization has occurred.(ABSTRACT TRUNCATED AT 400 WORDS)