IDENTIFICATION AND CHARACTERIZATION OF CELLS INFILTRATING THE GRAFT AND AQUEOUS-HUMOR IN RAT CORNEAL ALLOGRAFT-REJECTION

In a rat model of corneal transplantation, Fischer 344 (RT1(lv1)) rats received orthotopic corneal isografts or Wistar-Furth (RT1(u)) donor allografts. Rejection was observed in 25 of 26 allograft recipients, a t a median time of 18 days, with all isografts surviving > 100 days. F low cytometric analysis of aqueous humour identified cellular infiltra tion of the aqueous at the time of allograft rejection, in contrast to the acellular aqueous found in isografts at corresponding times follo wing transplantation. A higher proportion of CD8(+) than CD4(+) cells was found at days 1-3 following rejection, whereas there was a higher proportion of CD4(+) cells at days 5-8. No changes in peripheral blood T cell subsets were found at the time of rejection. Immunohistochemic al analysis of cells infiltrating recipient iris and grafted cornea un dertaken at days 1-2, 4 and 7-10 following onset of rejection, demonst rated inflammatory cells in the graft epithelium, stroma and aggregate d on the endothelium. Large numbers of macrophages, T cells (CD4(+) > CD8(+) at all time points), natural killer (NK) cells and neutrophils were detected in graft tissue at days 1-2 and 4, diminishing after tha t time. Most infiltrating cells expressed MHC class II antigen, and a smaller number expressed IL-2R. Expression of the co-stimulatory marke r B7 was identified in a few cells at day 4 in the region of the graft -host wound. The immune response in graft rejection was characterized at day 4 also by expression of intercellular adhesion molecule-1 (ICAM -1) on endothelial cells of iris and corneal vessels, demonstration of interferon-gamma on mononuclear cells in the peripheral (recipient) c ornea, and tumour necrosis factor-alpha on aggregated mononuclear cell s on the graft, but not recipient, endothelium. Only sparse cellular i nfiltrates were found in isograft controls, with inflammation located at the graft-host wound. These findings suggest that inflammatory cell s reach a corneal allograft by two routes-from vessels in the peripher al recipient cornea, and from vessels in the recipient iris via the aq ueous humour. Different aqueous and intragraft T cell subset proportio ns were seen early in rejection, although a preponderance of CD4(+) ce lls was found in both aqueous and graft at later times.