Conspiculatus,
I can find you several references of studies demonstrating this point. I would have to search again though. A better example would be immunotherapy in humans for a cutaneous Protozoal infection like leishmaniasis. humans are exposed to antigens in order to stimulate an immune response.
Badaro R, Lobo I, Munos A, et al. (October 2006). "Immunotherapy for drug-refractory mucosal leishmaniasis". J Infect Dis. 194 (8): 1151–9. doi:10.1086/507708. PMID 16991091.