Ingested dust mite favours sensitization to egg in mice independently of its proteinase activity

Despite it is well documented that house dust mite (HDM) can cause tissue damage and activate innate immune cells, its potential to promote gastrointestinal sensitization and allergenicity to food proteins has been relatively unexplored. This study aimed to determine the immunostimulant properties of HDM in the development of allergy to egg white (EW) when administered in a murine model of oral sensitization without exogenous adjuvant. The effect of its proteolytically inactivated form (iHDM) was also investigated to evaluate the contribution of protease activity to its potential adjuvant effect. HDM and iHDM stimulated allergy to unrelated egg allergens through the oral route as evidenced by signs of mast cell degranulation in the intestinal tract following challenge with the EW, although only iHDM induced detectable concentrations of serum EW-specific IgE and IgG1 antibodies. Although HDM affected the expression of genes encoding tight junction proteins and Th2-inducing alarmins in the intestine to a greater extent than iHDM, the presence of active proteinases was not a requirement for its adjuvant activity, since iHDM preferentially promoted Th2 responses in intestinal lymphoid tissues. These results suggest that the ingestion of environmental dust may favour food allergy initiation and highlight the complex and context-dependent nature of the adjuvant activity of HDM.