The goal of this study was to investigate the relationship between the presence of Class II antigen-expressing cells (Class II+) cells in the cornea and the generation of allograft immunity. Wistar/Furth (W/F) rat Class II+ cells were injected in various numbers (0.01, 0.1, 1.0, 5.0, 10.0, and 20.0 X 10(6) into the corneal stroma of Fischer 344 (F344) rats. For comparison, the same numbers of W/F Class II+ cells were injected directly into the peritoneal cavity of F344 rats. Also, W/F cells were injected into the corneas of F344 rats and the corneas were "grafted" intraperitoneally in F344 hosts. The results showed that up to 20 X 10(6) class II+ cells injected in situ into the corneal stroma did not elicit a serum cytotoxic antibody response or a splenic or blood cytotoxic T-cell response against donor Class II antigens. In contrast, systemic immune responses were elicited by both direct intraperitoneal injection of large numbers (10 or 20 X 10(6] of allogeneic Class II+ cells and by intraperitoneal grafting of syngeneic corneas carrying similar numbers of allogeneic Class II+ cells. F344 recipients of a syngeneic cornea containing 10 or 20 x 10(6) W/F Class II+ cells or a suspension of W/F cells exhibited an accelerated rejection of W/F skin allografts (13.3 versus 9.0 days, first- versus second-set rejection). These results indicate that the number of Class II+ cells required to elicit a systemic immune response is larger than the number of Class II+ cells present in the normal cornea.