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.

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