Immune response to a Trichinella spiralis infection in house mice from lines selectively bred for high voluntary wheel running.

Four lines of mice bred for high voluntary wheel running (HR lines) have high baseline circulating corticosterone levels and increased daily energy expenditure as compared with four non-selected control (C) lines. High corticosterone may suppress immune function and competing energy demands may limit ability to mount an immune response. We hypothesized that HR mice have a reduced immune response and therefore a decreased ability to fight an infection by Trichinella spiralis, an ecologically relevant nematode common in mammals. Infections have an acute, intestinal phase while the nematode is migrating, reproducing and traveling throughout the bloodstream, followed by a chronic phase with larvae encysted in muscles. Adult males (generation 55 of the selection experiment) were sham-infected or infected by oral gavage with ~300 J1 T. spiralis larvae. During the chronic phase of infection, mice were given wheel access for 6 days, followed by 2 days of maximum aerobic performance trials. Two weeks post-infection, infected HR had significantly lower circulating immunoglobulin E levels compared with infected C mice. However, we found no statistical difference between infected HR and C mice in numbers of encysted larvae within the diaphragm. As expected, both voluntary running and maximum aerobic performance were significantly higher in HR mice and lower in infected mice, with no line type-by-infection interactions. Results complement those of previous studies suggesting decreased locomotor abilities during the chronic phase of T. spiralis infection. However, despite reduced antibody production, breeding for high voluntary wheel exercise does not appear to have a substantial negative impact on general humoral function.