Class I chitinases with hevein-like domain, but not class II enzymes, are relevant chestnut and avocado allergens.

BACKGROUND

Several foods associated with the latex-fruit syndrome present relevant allergens of around 30 kd. Neither these components nor any other responsible for the reported cross-reactions have been identified and purified.

OBJECTIVE

We sought to isolate and characterize the 30 kd allergens from avocado fruit and chestnut seed, two of the main allergenic foods linked with latex allergy.

METHODS

Sera from patients allergic to chestnut and avocado were selected according to clinical symptoms, specific IgE levels, and positive skin prick test responses. Class I and II chitinases were purified by affinity and cation-exchange chromatography and characterized by specific IgE and anti-chitinase immunodetection, immunoblot inhibition assays, enzymatic activity tests, and N-terminal sequencing.

RESULTS

Relevant 32 kd allergens were detected by specific IgE immunodetection in both avocado and chestnut crude extracts. The same bands, together with others of 25 kd, were revealed by a monospecific antiserum against class II chitinases. Purification and characterization of the 32 kd allergens from both plant sources allowed their identification as class I chitinases with an N-terminal hevein-domain. The purified allergens fully inhibited IgE binding by the corresponding crude extract when tested in immunoblot inhibition assays. Highly related 25 kd class II chitinases that lack the hevein-like domain were also isolated from the same protein preparations. No IgE-binding capacity was shown by these class II enzymes.

CONCLUSIONS

Class I chitinases are relevant allergens of avocado and chestnut and could be the panallergens responsible for the latex-fruit syndrome. The hevein-like domain seems to be involved in their allergenic reactivity.