Der p I, a major allergen of the house dust mite, proteolytically cleaves the low‐affinity receptor for human IgE (CD23)

The nature of the proteases that cleave CD23 in vivo is of considerable interest, but remains unknown. Here, we demonstrate that Der p I, a major allergen of the house dust mite Dermatophagoides pteronyssinus, cleaves CD23 from the surface of cultured human B cells (RPMI 8866 B cell line). The cleavage of the receptor from the B cell surface was associated with a parallel increase in soluble CD23 (sCD23) in the culture supernatant. Furthermore, the proteolytic effect of Der p I was specific for CD23, since none of the other B cell markers tested (CD20, HLA‐DR, CD71 and CD49d) were affected. Labeled antibody experiments and protease inhibition assays clearly demonstrate that Der p I is a cysteine protease that directly cleaves a 25‐kDa fragment of CD23. These data suggest that the cysteine protease Der p I, in addition to being highly immunogenic, may up‐regulate IgE synthesis by virtue of its ability to cleave CD23.