Decreased immune responses against alloantigens in vitro of allogeneic full-term fetal blood recipients.

Mice were challenged with third-party newborn C3H/HeJ hearts in vivo 45 to 82 days before the assay. Spleen cells were isolated 200 days after transplantation and stimulated in vitro with irradiated C3H/HeJ spleen cells for proliferation and CTL assay. Sera were obtained on the same day for alloantigen-specific cytotoxic antibody assay. (A) Proliferation was determined by [³H]thymidine incorporation. (B) Cytotoxicity was assessed with⁵¹Cr-labeled 2-day Con A–activated C3H/HeJ spleen cells. Nonspecific release against irrelevant antigens (B10.D2) was performed to ensure the specificity of killing. (C) Third-party alloantigen-specific cytotoxic antibody was detected by microcytotoxicity assay. Two-day Con A–activated C3H/HeJ spleen cells were used as target cells. Dead cells were visualized by trypan blue. Each group contained 2 to 5 animals. *P < .05, compared with allogeneic T-cell–depleted bone marrow recipients.^#P < .01, compared with normal C57BL/6 mice. TCD indicates T-cell–depleted.