Local graft-versus-host reaction suppressed by immuno-blocking antibody secreted by antibody-forming cells transferred with the graft.

The graft versus host (GVH) reactivity of Lewis (L) rat spleen cells was measured using a popliteal lymph node (PLN) assay in Lewis-Brown Norway (LBN) recipient rats. Specific sensitization of donors with a single intravenous injection of LBN spleen cells 7-14 days prior to assay resulted in a significant decrease in GVH reactivity. Thirdparty sensitization of donors with Lewis-Buffalo spleen cells did not alter GVH reactivity. L spleen cells suspended in L anti-LBN serum were equally as reactive in the PLN assay as L spleen cells suspended in normal L serum. An association was observed between the degree of immunosuppression as a function of time after sensitization and the titer of cytotoxic antibody in the donor serum. This association was not shown in a study of GVH reactivity and serum cytotoxic antibody titer as a function of the number of cells used. Velocity sedimentation was used to separate spleen cells obtained from specifically sensitized L rats into fractions either enriched or depleted 5 6 of antibody-forming cells (AFC). The addition of 10 or 10 sensitized cells from the 7 AFC-enriched fraction to 10 normal spleen cells resulted in a significant decrease in GVH reactivity. The addition of 10 sensitized cells depleted in AFC did not significantly change the GVH reactivity of 10 normal L spleen cells. From these data we conclude that the suppression in GVH reactivity produced by donor sensitization can be accounted for by immunoblocking antibodies secreted by cells transferred with the graft.