A synthetic peptide administered with IL-12 elicits immunity to Listeria monocytogenes

IL-12 is a pivotal cytokine signal for the development of Th1-type cellular responses that are required for control of intracellular pathogens. We previously demonstrated that coinjection of IL-12 with heat-killed Listeria monocytogenes, which was not immunogenic when injected alone, elicited intense Ag-specific T cell responses that conferred protection against subsequent challenge with Listeria. Herein we describe the remarkable finding that a nonimmunogenic synthetic peptide corresponding to a dominant MHC class II (H-2k)-restricted listerial determinant, when coinjected i.p. with murine IL-12, elicited potent Ag-specific immune responses that conferred protective immunity against Listeria.