The role of soil exposure in asthma prevention during neonatal period To the Editor: We read with great interest the article titled ''Soil exposure modifies the gut microbiota and supports immune tolerance in a mouse model'' by Ottman et al. 1 The study investigated the effect and mechanism of soil exposure-induced immune tolerance. However, soil exposure to adults might not be practical in asthma treatment and prevention. Exposure to new microbiota might induce activation of innated and acquired immune system, which might lead to symptoms indicating intestinal inflammation, such as diarrhea. 2 Intestine microbiota of people from different areas varies greatly, and travel to a new area might cause traveler's diarrhea. 3 However, Ottman et al 1 did not show the pathology of intestine, severity of diarrhea, hematochezia, and weight loss during soil exposure and before sensitization and airway challenge in their study. The immune tolerance effect of soil exposure might be caused by rebalance of immunity and intestine microbiota. The neonatal period is the most proper period for soil exposure. Neonates were born to a relatively safe environment with extensive safe antigens and little pathogens. Thus, one of the major targets of the neonatal immune system is to build immune tolerance to environmental antigens. Several immune-suppressive cells have been found to induce immune tolerance to environmental antigens. 4 Soil exposure begins right after birth for mammals, which might play a significant role in immune tolerance and prevention of allergic diseases including asthma. 5 Thus, soil exposure should be a given for pregnant mice and should remain persistent during the neonatal period, which might lead to a more significant effect in reducing ovalbumin-induced lung inflammation.
