Effect of prolactin, rIFN-gamma or rTNF-alpha in murine toxoplasmosis

Mice lethally infected with T. gondii and treated with prolactin (PRL), recombinant interferon gamma (rIFN-gamma) or recombinant tumour necrosis factor (rTNF-alpha) were protected against death, as compared to untreated controls. The protective effect of PRL (0.5-2 mg/kg/twice daily for 12 days) was dose dependent and statistically significant (P < 0.001). The survival was 50% or 40% in mice that received doses of 1 x 10(4) U of rIFN-gamma or 4 x 10(4) U of rTNF-alpha at -2, 0, +2 days before and after infection (P < 0.0001). An increase of time to death, up to 60 days after challenge, and of survival rate (50% up to 70%) were observed in animals treated with PRL in combination with either rTNF-alpha or rIFN-gamma, compared to those that received treatments with the same therapeutic agents alone; however the differences were not statistically significant. In addition, a slight synergistic effect on brain cyst formation, with lower number of Toxoplasma cysts, was observed in mice treated with PRL plus TNF-alpha (P < 0.01), compared with animals that received rTNF-alpha alone (P < 0.05). These data suggest that PRL can regulate in vivo endogenous TNF-alpha production in the cytokine cascade. We conclude that prolactin may play an important role in modulating the host's immune defence against T. gondii opportunistic infection.