Altered energy balance and cytokine gene expression in a murine model of chronic infection with Toxoplasma gondii.

The temporal pattern of changes in energy balance and cytokine mRNA expression in spleen and brain were examined in a mouse model of infection with Toxoplasma gondii. During days 1-7 postinfection, food intake was unaltered, but energy expenditure was significantly increased, and this was associated with elevated tumor necrosis factor-alpha (TNF-alpha), interleukin (IL)-1, IL-5, and interferon (IFN)-gamma. The hypermetabolic state persisted during subsequent anorexia, whose onset coincided with elevated IL-2, and at the end of the acute phase of cachexia, the dual anorexic and hypermetabolic states were associated with the cytokines examined: TNF-alpha, IL-1 beta, IL-2, IL-4, IL-5, IL-6, IL-10, and IFN-gamma. In the chronic phase of the infection, the mice showed either partial weight recovery (gainers) or no weight regain (nongainers). The infected gainers, though still hypophagic, were no longer hypermetabolic, and their cytokine mRNA was no longer elevated, except for TNF-alpha and IL-10. In contrast, the infected nongainers continued to show both anoroxia and hypermetabolism, which were associated with elevations in all cytokines examined and particularly those of the TH2 profile (IL-4 and IL-5) and IL-6. Taken together, these studies reveal a distinct pattern of cytokine mRNA expression underlying 1) hypermetabolism vs. anorexia, 2) acute vs. chronic cachexia, and 3) stable weight loss vs. partial weight recovery.