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Pregnancy has an important impact on the maternal immune system, associated with a shift in the Th1/Th2 cytokine balance towards a type-2 response. However, listeria induced Th1 type cytokines are essential in host protection against this facultative intracellular bacterium. We have analyzed and compared the kinetics of maternal serum concentrations of IFN-γ, IL-10, TNF-α, IL-6 and KC by ELISA. Serum IFN-γ levels in infected pregnant mice were significantly reduced in comparison to infected virgin animals, while IL-10 levels were increased, being significantly higher on days 3 and 6 p.i. as compared to infected virgin mice. Upon L. monocytogenes infection, circulating TNF-α concentrations were below the detection limit. However, on day 6 p.i., in pregnant mice elevated levels of TNF-α were noticed, correlating to the severity of disease. Increased concentrations of IL-6 have been shown to follow the kinetics of bacterial numbers in the liver of infected animals. Murine chemokine KC production in maternal circulation followed a similar pattern as IL-6.

In comparison to virgin animals, pregnant mice mount lower levels of protective Th1 cytokines and are unable to eliminate the pathogen. Increased serum concentrations of IL-10, along with proinflammatory cytokines, may well contribute to the severity of pregnancy-associated listeriosis.

Maternal serum IL-6 level showed the highest correlation with the course of infection and pregnancy outcome.