Dynamics of the intracerebral and splenic cytokine mRNA production in Toxoplasma gondii-resistant and -susceptible congenic strains of mice.

Oral infection with a low-virulence strain of Toxoplasma gondii (Tg) induced a persisting encephalitis in resistant strains of mice. In the present study we have examined transcripts of various cytokines during acute and chronic stages of murine Tg encephalitis. In the brain of infected animals, interferon-gamma (IFN-gamma), tumour necrosis factor-alpha (TNF-alpha), interleukin-2 (IL-2), IL-6, IL-10 and IL-12 mRNA were induced to a significant extent, but only low levels of IL-4 mRNA were detectable. A similar cytokine profile was observed in the spleen. However, in contrast to the brain, the increase of IL-2 mRNA was particularly pronounced in the spleen, whereas the opposite was found for IFN-gamma and TNF-alpha mRNA. Thus, cytokines involved in T-cell proliferation were more prevalent in the spleen, but in the brain, where Tg actively multiplies, the effector molecules IFN-gamma and TNF-alpha were preferentially up-regulated. In addition, a detailed analysis of cytokine mRNA levels in major histocompatibility complex (MHC)-congenic strains of BALB and B10 mice revealed that the genetically regulated susceptibility to Tg was correlated with the amount of intracerebrally produced cytokine mRNA for IFN-gamma, TNF-alpha and IL-6. Mice with a strong increase of these cytokine mRNA were significantly better protected against Tg. This indicates that the outcome of toxoplasmosis may be critically dependent on an adequately regulated intracerebral immune response.