Immunotherapy comprises administration of an alkaloid at a dose sufficient to induce IL-2 production in dendritic cells in a patient. The alkaloid induces the production of IL-2 in dendritic cells. The alkaloids need not be naturally occurring, and may be synthetic analogues or derivatives of naturally occurring counterparts. Such analogues or derivatives are preferably pharmaceutically acceptable analogues, salts, isomers or derivatives as herein defined. However, preferred alkaloids are phytochemicals. Such phytochemicals may be isolated from natural sources or synthesised in vitro. Particularly preferred are alkaloids is selected from piperidine alkaloids; pyrrolin alkaloids; pyrrolidine alkaloids; pyrolizidine alkaloids: indolizidine alkaloids and nortropane alkaloids.