Heterogeneity of the tolerant state in rats with long established skin grafts.

Tolerance in rats with long established allogeneic skin grafts brought about by the neonatal inoculation of hybrid lymphomyeloid cells is immunologically heterogeneous because 2 states of tolerance may be defined operationally as fully and partially tolerant. T cells from fully tolerant donors transfer tolerance and are unresponsive in MLC, but T cells from partially tolerant donors do not transfer tolerance and are modestly responsive in MLC. A state of tolerance may exist without detectable suppression. Therefore, tolerance, traditionally defined as the permanent acceptance of an allogeneic skin graft, does not reflect a uniform immunologic state.