Allergen-induced disulfide-linked dimers/oligomers of histamine-releasing factor enhance mast cell activation

Abstract Objective We are investigating the role of disulfide-linked HRF dimers/oligomers in facilitating allergen-induced anaphylaxis. Results Our lab has previously shown that IgE can act as a receptor for histamine-releasing factor (HRF). Interestingly, HRF dimers and oligomers are able to activate mast cells in an HRF-reactive IgE-dependent manner, whereas HRF monomers cannot. HRF homo-dimerization occurs via disulfide bonding through its C-terminal residue, cysteine 172 (C172). We have found that secretion of HRF dimers/oligomers in the small intestine is more abundant in food allergic than non-allergic mice. To investigate the role of C172-mediated HRF di-/oligomerization in allergic reactions, we generated a transgenic HRF-C172A mouse in which HRF’s C172 was substituted with alanine. Using ovalbumin-induced food allergy and passive systemic anaphylaxis experiments, we showed that the HRF-C172A mice exhibit much weaker anaphylactic responses compared to their wild-type counterparts. In vitro experiments showed that antigen/IgE-mediated mast cell activation is maintained in the C172A mice, indicating that mast cell functionality is intact in the mutant mice. Since both of the in vivo experiments represent IgE/mast cell-dependent models of anaphylaxis, the differences in phenotype demonstrate the crucial role of disulfide linkage of HRF dimer/oligomers in IgE-mediated anaphylaxis. We also show that HRF dimerization is mediated by disulfide-bond-forming Ero family members and related enzymes. Conclusion Disulfide-linked HRF dimer/oligomers are a key factor in enhancing anaphylactic symptoms in the murine allergy models.