Allergy is a global disease with overall frequencies of >20%. Symptoms vary from irritating local itching to life-threatening systemic anaphylaxis. Even though allergies are allergen-specific, there is a wide range of cross-reactivities (eg apple and latex) that remain largely unexplained. Given the abilities of low-affinity IgG antibodies to inhibit mast cells activation, here we elucidate the minimal affinity of IgE antibodies to induce type I hypersensitivity.
Three mature (high-affinity) IgE antibodies recognizing three distinct epitopes on Fel d 1, the major cat allergen, were back-mutated to germline conformation, resulting in binding to Fel d 1 with low affinity. The ability of these IgE antibodies to activate mast cells in vitro and in vivo was tested.
We demonstrate that affinities as low as 10-7  M are sufficient to activate mast cells in vitro and drive allergic reactions in vivo. Low-affinity IgE antibodies are able to do so, since they bind allergens bivalently on the surface of mast cells, leading to high-avidity interactions.
These results suggest that the underlying mechanism of allergen cross-reactivity may be low-affinity but high-avidity binding between IgE antibodies and cross-reactive allergen.

BACKGROUND: Allergic rhinitis and bronchial asthma are common allergic diseases. The pattern of dominant allergens depends on the degree of urbanization and the geographic region. The present study characterized the allergens of patients with allergic rhinitis and bronchial asthma in Ningxia region of China.
METHODS: A total of 309 patients were enrolled in this study. Western blotting assays were performed of the serum samples to evaluate allergen-specific IgE antibody for inhaled and ingested allergens. Statistical analysis was performed to compare the positive rate among different subgroups.
RESULTS: Among the 309 patients, 221 of them had positive test results. There were 157 positive cases for ingested allergens and 174 positive cases for inhaled allergens. No significant differences in positive rates were found between the ingested and inhaled allergens. Among the inhaled allergens, Artemisia was the most frequent allergen, followed by fungi and dog hair. Cashew was the most common ingested allergen, followed by crab, mango, and beef. Further analysis showed no significant differences in positive rate between males and females. However, significant differences in positive rate of inhaled and ingested allergens were found between children (1-13 years old) and adults (above 18 years old) (P < .05), while no significant differences were found between the children and teenagers (14-18 years old). For the comparison between teenagers and adults, significant difference in positive rate was found only in the ingested allergen.
CONCLUSIONS: This study provided the characteristics of allergens in Ningxia population, providing clinical and epidemiological data for prevention and treatment of the diseases in the region.