Studies on transplantation immunity

Elimination of allogeneic lymphocytes by mice

Two major classes of response to allogeneic lymphocytes can be detected in mice in vivo, based on injecting them intravenously with 51Cr-labelled lymph node cells and examining them in a short term assay. A natural immunity discriminating between allogeneic and syngeneic lymphocytes is seen in the lymph nodes (and to a lesser extent, the spleen), which has such close similarities to natural cell-mediated responses of the NK class as thymic-independence and radioresistance. However, it has immunological specificity of a conventional kind, probably towards serologically determined K/D antigens. There is also an active immune response, produced by immunisation with dissociated lymphoid cells or allografting, which consists of three elements: an IgG opsonising alloantibody response, diverting circulating lymphocytes to the liver; an IgM opsonin, localising them to the spleen; and a cell-mediated serum-dependent elimination mechanism that destroys cells entering the lymph nodes and spleen. Dose-response curves for the primary response show evidence of high-dose paralysis of elimination. Dose-time-response results for the secondary show a variety of unique characteristics; evidence is presented to suggest that several aspects of the phenomenon betray primitive features retained from an earlier stage in the evolution of the immunological system.

Studies on transplantation immunity. IV. Murine natural immunity to lymphoid cells in vivo

A natural response acting to discriminate between allogeneic and syngeneic lymphocytes in vivo is described for normal mice. Eighteen to 24 h after systemic injections of low doses of 51Cr-labeled cells, less radioactivity is found in the lymph nodes after allogeneic transfer. The spleen but not the liver participates in the response. It can be abolished by neonatal induction of transplantation tolerance, is shown to be immunologically specific, and is resistant to irradiation up to 1000 rd, although a radiosensitive phase occurs during recovery from sublethal irradiation. The response is cell-mediated but depends upon cooperation from a factor present in normal serum. It is thymus-independent: this clearly distinguishes it from the superficially similar immune response acquired by immunization and aligns it with the class of responses to which the hybrid histocompatibility response and natural killer-like phenomena belong. Unlike these, however, it is present at birth and directed primarily against H-2 antigens. It appears to follow the classical transplantation rules in a limited range of strains. Some of the difficulties inherent in this type of study are discussed.