Endogenous testosterone levels do not affect filarial worm burdens in mice

It has been observed for several years that males of many mammalian species exhibit higher prevalence and intensity of parasitic infections than females. It has been theorized that this sexual dichotomy may be due to the immunosuppressive properties of testosterone. The administration of exogenous testosterone to laboratory animals often results in higher yields of several parasitic nematodes, lending credence to this hypothesis. We sought to determine if worm burdens in individual mice were related to serum testosterone concentrations. We found that in a cage of five male mice, one or two individuals exhibited high circulating testosterone levels, while the rest had low to undetectable levels. Serum testosterone did not correlate with worm recoveries. The implications of these findings are twofold. First, our data suggest that high endogenous testosterone does not necessarily decrease the ability of mice to resist nematode infection and second, that results obtained from administration of exogenous testosterone should be interpreted with caution.