Identification and characterization of cross-reactive natural rubber latex and Ficus benjamina allergens

An association between allergy to Ficus benjamina and natural rubber latex (NRL) has been suspected based on clinical and immunological observations. The responsible cross-reactive allergens have not been identified yet. This study was undertaken to investigate the cross-reactivity between hevein (Hev b 6.02, 4.7 kD), a major allergen of NRL, and F. benjamina and identify its counterpart in F. benjamina.

89 serum samples from subjects allergic to NRL were used in the study. Skin prick tests were performed with highly purified hevein and sap extract of F. benjamina. Specific IgE antibodies to NRL, F. benjamina and Hev b 6.02 were determined by the Pharmacia CAP method. Cross-reactivity among these allergens was investigated by means of CAP and immunoblot inhibition experiments. Two-dimensional gel electrophoresis separation and protein microsequencing were performed to identify the cross-reactive allergens in F. benjamina.

67 out of 89 (75%) sera showed elevated IgE to hevein. Specific IgE to Ficus were found in 22 (24.7%) sera, and with 1 exception, all these sera also had IgE to Hev b 6.02. Results of CAP inhibition assays using 11 sera showing IgE to both Hev b 6.02 and Ficus demonstrated that the IgE to Ficus could be completely inhibited by Hev b 6.02 in 6 of 11 sera. Immunoblots and immunoblot inhibition assays revealed that a protein of about 45 kD in F. benjamina is strongly recognized by serum IgE. In addition, the IgE-binding reactivity to this 45-kD protein could be completely inhibited by preincubation of the sera with Hev b 6.02. N-terminal protein sequencing of 14 amino acids indicated that this 45-kD protein has a hevein-like domain at the N-terminal region and may belong to the endochitinase family.

Latex-allergic patients are at higher risk of becoming sensitized to Ficus. Hev b 6.02 in latex is a major cross-reactive allergen and its counterpart in F. benjamina is an acidic protein with a molecular weight of about 45 kD and a hevein-like N-terminal domain.