Mechanisms in immune tolerance. I. A specific block of immunological memory in HSA-tolerant mice

Evidence is provided indicating that the transient immune response detected during the induction of tolerance to HSA in mice, results in immunological memory which persists in an immunosuppressed state in the tolerant animals. The mechanism which blocks this memory is antigen-specific and can be selectively inactivated by total body irradiation in the range of 650–900 R. Consequently tolerant mice, irradiated within this range and restored with normal syngeneic spleen cells, respond better to the tolerizing antigens than do similarly treated normal mice. The tolerizing block can be transmitted from “tolerant” to normal spleen cells when a mixture of both is transferred to normal irradiated recipients. Since similar inhibitory activity is also demonstrated by fresh sera of tolerant mice, it is suggested that the blocking mechanism depends on inhibitory cells which act via a humoral inhibitor.