Cp. Larsen et al., FAS-MEDIATED CYTOTOXICITY - AN IMMUNOEFFECTOR OR IMMUNOREGULATORY PATHWAY IN T-CELL-MEDIATED IMMUNE-RESPONSES, Transplantation, 60(3), 1995, pp. 221-224
Fas/Fas ligand interactions serve as a signaling pathway for apoptosis
(1-3), an important regulatory mechanism in the development and funct
ion of the immune system (4-9). Recent evidence that Fas-dependent apo
ptosis is also an important mode of T cell cytotoxicity (10-13) sugges
ted that Fas might play a critical role in the effector phase of T-dep
endent immune responses, such as allograft rejection. We observed that
Fas transcripts are constitutively expressed in syngeneic and allogen
eic murine cardiac transplants, while Fas ligand (Fast) is up-regulate
d only in rejecting allografts. Surprisingly, the absence of an intact
Fas/FasL pathway did not alter the tempo of allograft rejection, even
CD4-dependent rejection. These results indicate that Fas/FasL interac
tions are not essential mediators of T cell-induced allograft damage.
Rather, as suggested in other studies, the Fas pathway may be principa
lly involved in the regulation of clonal expansion and subsequent cont
raction of T cell populations during immune responses.