Reduced cytotoxic responses with normal CTL precursor numbers in tolerant mice

Balb/c (H-2d) thyroid lobes were cultured for 48 hours in 2.5 atmospheres of O2 and inserted under the kidney capsule of C57B1/6 (H-2b) mice. 36 out of 52 grafts survived for more than 30 weeks. Unlike freshly grafted mice long term recipients failed to reject the original grafts or a new transplant following the injection of donor spleen cells. Cytotoxic T lymphocytes precursor (CTLp) frequency was found to be in the same range (1/500 to 1/1000 spleen cells) in tolerant and normal mice. Nevertheless CTL responses were reduced both in vivo and in vitro. CTL responses in vivo were measured by injecting live P815 tumor cells (H-2d) i.p. into primed tolerant and normal C57B1/6 mice. The peak of specific 51Cr release (E:T = 80:1) of 9 normal mice was 39 +/- 7% on day 3, while the peak response of 11 tolerant mice was 12 +/- 2% on day 5. CTL responess measured in vitro were less strinkingly reduced than the in vivo responses. However, the in vitro responses were reduced in different experiments by either (1) reduced specific 51Cr release at the same E:T ratio or (2) reduced cell number at the end of the culture. Further evidence that the in vitro CTL responses of tolerant mice were suppressed was found in their restoration to normal levels by the addition of ConA supernatant to the culture media