Natural and synthetic polymers of nucleic acids have been shown to enhance humoral antibody responses to sheep red blood cells and bovine γ globulin (1–4). The double stranded RNA, polyinosinic-polycytidylic acid (poly I:poly C), is a potent inducer of interferon production (5) and recently has been demonstrated to inhibit the growth of some types of tumors in mice (6). One explanation for the anti-tumor activity of poly I:poly C may be that it acts as an adjuvant in cellular immune reactions, causing enhanced immunologic rejection.

In order to test this hypothesis, spleen cells obtained from animals that were treated with poly I:poly C were injected into neonatal recipients. Graft-vs-host (GVH) reactions that resulted were compared to those obtained with spleen cells from untreated donor animals using a quantitative spleen-weight assay.

Materials and Methods. A modification (7) of the spleen assay described by Simonsen (8) was performed. The assay is based upon the observation that splenomegaly in recipient neonatal F1 mice is an early and constant finding following injections of lymphoid cells obtained from mice of one parental strain.

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