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.