Role of natural killer cells in the rejection process of corneal allografts in rats.
BACKGROUND
The exact mechanism of human corneal allograft rejection, which is the major cause of corneal transplant failure, remains unclear. We investigated the role of natural killer (NK) cells in rat corneal allograft rejection by examining the aqueous humor (AH) cell infiltrate on different postoperative days.


METHODS
Flow cytometric analysis was performed on the AH and submandibular draining lymph node (DLN) cells before transplantation and at different time points thereafter. In addition, we performed functional cytotoxicity assays with cells present in the AH during corneal rejection.


RESULTS
We demonstrated a gradual increase in the absolute cell number of different hematopoietic subpopulations in the AH after allogeneic cornea transplantation. CD3CD4 cells, mainly monocytes and macrophages, were the predominant subpopulation 2 days after transplantation, followed by a successive relative increase of CD4 T cells, CD8 T cells, CD161 T cells, and NK cells. NK and CD161 T cells were present at a 10- to 15-fold higher percentage than in the DLN, suggestive of local expansion of these cells. A higher percentage of NK cells were CD8-negative compared with DLN NK cells. AH cells specifically lysed allogeneic cells, and this cytotoxicity was mainly attributable to NK cells but not to CD4 or CD8 T lymphocytes.


CONCLUSIONS
These results confirm the crucial role of CD4 cells in the allogeneic corneal graft rejection process and implicate NK cells as possible mediators of the rejection.
Claerhout
Ilse
I
Department of Ophthalmology, Ghent University Hospital, Ghent, Belgium. ilse.claerhout@UGent.be
Kestelyn
Philippe
P
Debacker
Veronique
V
Beele
Hilde
H
Leclercq
Georges
G
D000818:Animals; D001082:Aqueous Humor / Q000166:cytology / Q000276:immunology; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology; D016827:CD8 Antigens / Q000032:analysis; D018414:CD8-Positive T-Lymphocytes / Q000276:immunology; D016039:Corneal Transplantation / Q000276:immunology*; D006084:Graft Rejection / Q000276:immunology*; D007694:Killer Cells, Natural / Q000276:immunology*; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D014184:Transplantation, Homologous
D016827:CD8 Antigens