Microevolutionary response of a gut nematode to intestinal inflammation.

Parasitic helminths interfere with the immune response of their hosts to establish long-lasting, chronic infections. While favorable to the parasite, the capacity to dampen the immune response can also provide a benefit to the host in terms of reduced risk of immune disorders and immunopathology. The immunomodulatory role of nematodes has been exploited in clinical trials to treat a number of inflammatory and immune diseases. However, how parasites adapt to an inflammatory environment remains a poorly explored question. Here, we conducted a serial passage experiment where the gut nematode Heligmosomoides polygyrus was maintained for nine generations in mice with a drug-induced intestinal inflammation or in control hosts. The life history traits of parasites from the selected lines were assessed in hosts that were either exposed to the inflammatory environment or kept as controls. In addition to the nematode life history traits, we assessed the severity of the intestinal inflammation. We found that H. polygyrus adapted to the inflammatory environment through both plastic and microevolutionary responses. In particular, per capita fecundity was globally enhanced in worms that experienced intestinal inflammation and that were selected in the inflammatory environment. Interestingly, we also found that worms selected in the inflammatory environment were better able, after nine generations of selection, to alleviate the inflammatory symptoms. This latter result further highlights the potential therapeutic role of gut nematodes in the treatment of inflammatory diseases.