Partial reversal of radiation-induced immunosuppression by T-lymphocyte lysate.

BN rats were irradiated with 500 rad of 60Co 1 day before immunization with 0.1 mg of ovalbumin in alum hydroxide gel. The onset of reaginic and haemagglutinating antibody synthesis was suppressed to a non-detectable level for at least 3-4 weeks. When these irradiated rats were injected intraperitoneally with 10(8) viable or sonicated thymocytes 1 day after irradiation, the suppressed reaginic and haemagglutinating antibody synthesis was successfully restored. This suggests that: (i) thymocytes can restore the radiation-induced immunosuppression, but viability of thymocytes is not essential in this immune restoration; (ii) active biological molecules exist in the cytoplasmic pool of the normal thymocytes which can restore the radiation-induced immunosuppression; and (iii) the thymus not only plays a central role in the normal morphological development of the lymphoid system and its functional immunological maturation, but may also play an important role in the reversal of radiation-induced immunosuppression. To investigate tissue specificity of the factors that are actively engaged in the restoration of the suppressed immune response, peripheral lymphocytes, spleen cells, bone marrow cells and kidney cells were also tested. The results demonstrated that both peripheral lymphocytes and spleen cells could restore the suppressed immune response, but not bone marrow cells or kidney cells. This suggests that the active factors may be present only in T lymphocytes. Since the active factors could be found in the tissues other than thymocytes and non-stimulated lymphocytes, they appear to be different from thymosin, transfer factor or lymphokines derived from sensitized lymphocytes, and they were most likely not synthesized de novo.