PERSISTENT PRODUCTION OF INTERFERON-GAMMA (IFN-GAMMA) AND IL-12 IS ESSENTIAL FOR THE GENERATION OF PROTECTIVE IMMUNITY AGAINST LISTERIA-MONOCYTOGENES

IFN-gamma and IL-12 are believed to be important in the host defence a gainst Listeria infection in mice. However, the relationship between t hese two cytokines and generation of protective immunity remains poorl y understood. In the present study, it was found that at least 4 days of immunizing infection were required for the generation of protective immunity against L. monocytogenes. Protective immunity was generated only by immunizing infection with virulent strain. Even repeated injec tions of avirulent strain failed to induce protective immunity. When t he immunizing infection was terminated with antibiotics, generation of protective immunity and IFN-gamma-producing ability was impaired, whi le expression of IFN-gamma and IL-12 was also impaired. The mutual rel ationship between IFN-gamma and IL-12 in L. monocytogenes infection wa s analysed in vitro. After neutralization of IL-12, IFN-gamma producti on was completely blocked and IFN-gamma expression was also inhibited. In contrast, there was no change of IL-12 expression after neutraliza tion of IFN-gamma. Taking all facts into consideration, it may be conc luded that persistent production of IFN-gamma induced by persistent pr oduction of IL-12 during immunizing infection is essential for the gen eration of protective immunity against L. monocytogenes.