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The fetal lamb was found to reject orthotopic skin homografts applied at any time after the 77th day of gestation. Prior to this, grafts remained in place without stimulating any detectable immunologic response. Once the fetus achieves the ability to reject the graft, the process occurs with the same competence and rapidity as in the adult. Graft rejection in the fetal lamb is unaccompanied by formation of plasma cells or by the production of typical immunoglobulins, thus supporting the suggestion that circulating antibody does not play an obligatory role in the process.

Specific rejection of sterile orthotopic skin homografts by the fetal lamb in utero was unaccompanied by the presence of plasma cells in either the graft and its bed, or in the reactive draining lymph node. The grafts appeared not to stimulate the production of circulating immunoglobulins. The presence in the fetal circulation of rabbit anti-sheep 7S gamma-globulin and anti-beta(2M)-globulin did not inhibit the normal course of homograft rejection. These data support the contention that conventional circulating antibody is not an obligatory participant in the rejection of solid-tissue homografts.