THE DIFFERENTIAL-EFFECTS OF DONOR VERSUS HOST LANGERHANS CELLS IN THE REJECTION OF MHC-MATCHED CORNEAL ALLOGRAFTS

The fate of MHC-identical, multiple minor H-disparate corneal grafts was examined in the rat. Although skin grafts exchanged between LEW and F344 rats were invariably rejected, only 26% of the corresponding corneal grafts underwent rejection. The immunologic privilege of the minor H-disparate corneal grafts was due, at least in part, to the absence of donor-derived Langerhans cells. Corneal grafts were normally devoid of donor-derived Langerhans cells; however, grafts pretreated with latex beads became infiltrated with donor-derived Langerhans cells and were rejected by 59% of the naive minor H-compatible recipients. By contrast, untreated LEW corneal grafts underwent rejection in 26% of the naive F344 hosts even though the grafts became heavily infiltrated with host-derived Langerhans cells. The immunologic privilege of minor H-disparate corneal grafts was not the result of efferent blockade or suppression of the immune response. F344 hosts bearing long-term surviving LEW corneal allografts were challenged with LEW skin grafts. In all cases, orthotopic skin grafts were rejected acutely. Moreover, all previously clear corneal grafts underwent rejection following skin graft rejection. Thus, the unique absence of donor-derived Ia+ passenger cells and the avascular graft bed conspire to provide the primary minor H-disparate corneal graft with an immunologic privilege not shared by other organ grafts.