Abstract
Fever, a component of our innate immunity, is suppressed in late pregnancy. This likely contributes to protecting the foetus from harmful temperatures that increase the risk of complications for mother and foetus. Our laboratory has shown that late-pregnant mice injected with the bacterial mimetic, lipopolysaccharide (LPS), do not have a fever but exhibit other sickness symptoms like reduced food intake, and body weight. As fever can also arise from viral infections, we aimed to establish a viral model of fever suppression in late pregnancy using the viral mimetic, polyinosinic:polycytidylic acid (poly I:C). We hypothesised that poly I:C will not induce a fever in late-pregnant mice compared to non-pregnant mice.
To investigate this, wild-type mice were injected with saline and poly I:C while radiotelemetry recorded body temperature. In non-pregnant mice (n=3) injections were randomized counterbalanced on dioestrus. Pregnant mice (n=3) were injected with saline on day 17 and poly I:C on day 18 of pregnancy. Supporting the hypothesis, non-pregnant mice had significantly higher body temperature when injected with poly I:C compared to late-pregnant mice (repeated-measures two-way ANOVA, P = 0.0063).
Along with the absence of a fever, pregnant mice displayed sickness symptoms with reduced food intake (1.83 ± 0.09 g compared to 3.70 ± 0.31 g (presented as mean ± SEM) (repeated-measures two-way ANOVA, P = 0.0005) and body weight (-1.49 ± 0.03 g compared to 0.60 ± 1.60 g, repeated-measures two-way ANOVA, P = 0.0009) when injected with poly I:C compared to saline.
These data suggest that regardless of the origin of infection, mice have a suppressed fever in late pregnancy but still become sick. Future research could use these two models to elucidate the mechanism leading to fever suppression during pregnancy and ultimately strive to improve maternal health.