Recruiting CD33 on mast cells to inhibit IgE-mediated mast cell-dependent anaphylaxis.

IgE-mediated activation of mast cells is a hallmark of an anaphylactic reaction to allergen. In this issue of the JCI, Duan et al. describe an approach for suppressing IgE-dependent mast cell activation, thereby suppressing anaphylaxis. Specifically, the authors show that delivery of liposomes containing both the specific antigen recognized by the mast cell-bound IgE and a high-affinity glycan ligand of the inhibitory receptor CD33 (CD33L) to targeted mast cells inhibits antigen-induced, FcεRI-dependent spleen tyrosine kinase (Syk) phosphorylation and downstream protein tyrosine kinase (PTK) phosphorylation, Ca++ flux, and β-hexosaminidase release (i.e., degranulation). However, this strategy only worked if both the antigen (reactive with the mast cell-bound IgE) and CD33L were on the same liposome. This approach promises to rapidly reduce IgE-dependent mast cell activation in response to challenge with offending allergens.