The rapid rejection of allogeneic lymphocytes by a non-adaptive, cell-mediated mechanism (NK activity).

The fate of allogeneic lymphocytes (AO or DA) transferred to non-immune PVG recipients was studied in the light of previous evidence (Heslop & McNeilage, 1983; Rolstad & Ford, 1983) that allogeneic lymphocytes can be rapidly destroyed in certain strain combinations of rats and mice by a mechanism that is distinct from either T-cell mediated immunity or an alloantibody response. AO lymphocytes injected into PVG recipients were discriminated from syngeneic lymphocytes within 15-30 min of i.v. injection, as testified by the excess release of 51Cr into the lymph plasma of the recipient. The following experiments were intended to distinguish between natural antibody and natural killer (NK) cells as the mechanism responsible for the allogeneic lymphocyte cytotoxicity (ALC) displayed by PVG rats. Nude rats treated from birth with anti-mu chain serum and shown to be lacking B and T lymphocytes, as well as being profoundly deficient in immunoglobulin, displayed more aggressive ALC than did control nude rats which, in turn, showed stronger ALC than did euthymic rats. Serum from PVG nude rats exerted no inhibitory or destructive effect on allogeneic lymphocytes in an antibody-dependent cellular cytotoxicity system, an assay of graft-versus-host activity, or when injected into 3-4-week-old PVG rats which had not yet developed ALC. Treatment of nude rats with anti-asialo GM 1 antiserum depressed ALC and NK activity in parallel, thus adding to a wide range of circumstances in which ALC and NK activity are closely correlated. In conclusion, ALC is implemented by a non-adaptive, cell-mediated mechanism independent of immunoglobulin, but the precise identity of the effector cell in the recipients' lymphatic tissues remains to be settled.