Immunomodulatory Effects of Orally-Administered Saponins and Nonspecific Resistance against Rabies Infection

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Abstract
We present evidence that orally fed Quillaja saponins offer nonspecific resistance to mice against rabies viral infection. Adoptive transfer of spleen cells and thymocytes from animals preconditioned with saponin (SAP), inactivated rabies antigen (AG), or a mixture of AG+SAP has offered significant protection against an intracerebral challenge with live rabies virus. Levels of serum rabies-neutralizing antibodies in the different groups of recipient animals did not correlate with the respective survival rates. Culture supernatants of concanavalin A-stimulated spleen cells from animals fed SAP or AG+SAP induced marked T cell and B cell proliferation, and also greatly enhanced the plaque-forming cell activity of unprimed spleen B cells. Irrespective of the presence or absence of rabies-specific antibodies, sera from animals fed a mixture of AG+SAP induced significant levels of cell proliferation and augmented phytohemagglutinin (PHA)-induced responsiveness of spleen lymphocytes in vitro. The addition of sera from animals fed AG alone resulted in inhibition of cell proliferation and suppressed PH A-induced responses.