Sensitization and anaphylactic properties of main egg-white allergens in an animal model

Resumen

Egg allergy is one of the most common food allergies of childhood with an estimated prevalence of 2.6 %. One of the most abundant egg white proteins, ovalbumin (OVA), ovomucoid (OM) and lysozyme (LYS) are clinically relevant allergens, however their contribution to the allergenic potential of egg white is not known. The aim of this study was to compare the ability of these proteins to induce sensitization and elicitation of the allergenic response, using a mouse model of egg-allergy. [Methods]: Six-week-old female BALB/c mice were orally sensitized during 7 weeks either with 1 mg of OVA, OM or LYS. On week 8, each group of mice was orally challenged with 20 mg of the sensitizing protein. If no response was observed, increasing doses of the egg protein was administered i.p. Anaphylactic severity was evaluated by mMCPT-1 levels, clinical signs (ranging from 0, no reaction to 5, death) and rectal temperature 30 minutes upon challenge. Protein specific-IgE was measured by ELISA. Spleens and mesenteric lymph nodes were cultured, stimulated with OVA, OM and LYS and the immune response was evaluated by quantification of Th1 (IFN-γ) and Th2 (IL-4, IL-5 and IL-13) cytokines. [Results]: A significantly higher temperature drop (3.7 º and 1.7 ºC) and severe anaphylactic signs (score 3) were observed following oral challenge in LYS- and OM-sensitized groups as compared with the OVA-sensitized group. mMCPT-1 values were significantly increased (P<0.001), although they did not differ among the sensitized groups. Mice sensitized to LYS generated the highest specific IgE response 15 days after sensitization had started. However, after challenge, the highest levels corresponded to OVA- and OM-specific IgE. LYS stimulated an important production of Th2 cytokines (IL-4 and IL-13) as compared with OVA and OM (P<0.05). Spleen production of IFN-γ was significantly enhanced (P<0.05) in OM and LYS sensitized groups in comparison with OVA sensitized mice. [Conclusion]: Among the main egg allergens, LYS together with OM triggered the strongest anaphylactic responses. LYS also induced early production of specific IgE during the sensitization and strong Th1 and Th2 responses by splenocytes. These results point at LYS as the immunodominant allergen in egg white in this animal model.