Functional clonal deletion in immunological tolerance to major histocompatibility complex antigens.

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Abstract
CBA (H-2k) mice were rendered tolerant to H-2d antigens by injection of (CBA .times. BALB/c)F1 spleen cells at birth. At intervals of 2 days to 12 wk, the frequencies of anti-H-2d cytotoxic T lymphocyte precursor cells (CTL-P) in thymus and spleen were determined by using a limiting-dilution microculture assay system for CTL-P. This assay, utilizing irradiated H-2d stimulator cells and concanavalin A-induced spleen cell conditioned medium, was linear over the range 30-100,000 responder cells and was uninfluenced by IJ-positive cells. A profound and long-lasting deficit in activatable CTL-P, first demonstrable by day 5 of life in the thymus and day 8-10 in the spleen, developed in mice rendered tolerant, reaching a > 95% reduction by 6 wk. Functional clonal deletion thus seems to be at least as important in the tolerant state as suppressor T cells. Repeated in vivo administration of anti-IJk serum partially inhibited clonal deletion, suggesting that suppressor T cells are actively involved in producing clonal deletion or that IJk-bearing cells in the donor inoculum or the host represent an important factor.