Schistosoma japonicum infection downregulates house dust mite-induced allergic airway inflammation in mice.

The "hygiene hypothesis" is a theory try to explain the dramatic increases in the prevalence of autoimmune and allergic diseases over the past two to three decades in developed countries. According to this theory, reduced exposure to parasites and microorganisms in childhood is the main cause for the increased incidences of both T helper 1 (Th1)-mediated autoimmunity and Th2-mediated allergy. In this study, we investigated the impact of Schistosoma japonicum infection on the allergic airway inflammation induced by repeated intracheal inoculations of house dust mites (HDM), which is a Th17 and neutrophils dominant murine asthma model, mimicking severe asthma. We found that S. japonicum infection downregulated airway hyperresponsiveness. The infiltrating cells, Th17 and Th2 effector cytokines in the bronchoalveolar lavage (BAL) fluids and lungs were significantly reduced in the infected mice. Our findings indicated that S. japonicum infection was able to effectively inhibit host's allergic airway inflammation, which may be related to the upregulated Treg cells upon infection. To our knowledge, it is the first study to reveal the impact of S. japonicum infection on house dust mite induced severe asthma. More in depth investigation is need to elucidate the underlying mechanisms.