Studies on the Mechanism of Immunological Enhancement of Tumor Homografts. III. Interaction Between Humoral Isoantibodies and Immune Lymphoid Cells2

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Abstract
Immunological enhancement was studied specifically to demonstrate the possible occurrence of “efferent” inhibition of transplantation immunity caused by humoral antibodies. Enhancement could be induced in preimmunized foreign recipients by treatment of tumor cells with antibodies in vitro before their inoculation. Tumor cells coated with humoral isoantibodies had a lower capacity to absorb antibodies of the same specificity than untreated cells, as their antigenic receptors seemed partially blocked and could no longer react with antibodies. Passive transfer of humoral antibodies into preimmunized recipients prevented an efficient secondary response. The experiments suggested that enhanced growth of antiserum-treated tumor cells in preimmunized recipients may be caused by a dual effect of antibodies, an “afferent” inhibition of transplantation immunity inhibiting the development of the secondary response and an “efferent” suppression of the homograft reaction protecting the tumor cells from destruction by the immune effector mechanisms. The protective effect of antibodies was studied. Tumor cells were mixed with antibodies and immune lymphoid cells and inoculated into foreign hosts or recipients which were compatible with the tumor cells and lymphoid cells. Antibodies antagonized the neutralizing effect of immune lymphoid cells efficiently in foreign recipients, caused partly by inhibition of the homograft reaction of the host itself and partly by protection of the tumor cells. Protection by humoral antibodies was also demonstrated in compatible recipients and, since the homograft reaction could not interfere, the effect of antibodies could be ascribed exclusively to “efferent” inhibition of transplantation immunity.

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