Conjunctival allergenicity-supporting factor (CASF) in DIIIa as the sea squirt antigen capable of inducing asthmatic attack and conjunctival reaction in sea squirt asthma.

Among three glycoproteins, DIIIa, Ei-M, and Gi-rep, isolated from sea squirt as antigens capable of eliciting skin reaction specific to sea squirt allergy, only DIIIa induces asthmatic attack and conjunctival reaction, whereas Ei-M and Gi-rep do not. Periodate oxidation eliminated not only the conjunctival allergenicity but also the skin allergenicity from DIIIa, suggesting that the conjunctival and skin allergenicity could both be ascribed to the epitope residing in the carbohydrate chains of DIIIa. On the other hand, proteolysis with Pronase E and chemical modifications of the carboxyl or amino groups by various methods eliminated the conjunctival allergenicity from DIIIa, whereas the skin allergenicity was still retained. Therefore, the expression of conjunctival reaction was expected to be supported by a relatively small structural factor residing in the protein moiety of DIIIa, which we have tentatively designated as conjunctival allergenicity-supporting factor (CASF). CASF might contribute to the permeability of the antigen into mucosa, enabling the carbohydrate epitope to interact with the allergy-specific IgE distributed in conjunctiva and bronchi . In specificity analysis of a rabbit anti-DIIIa serum, a periodate oxidation- and acid-stable but heat- and alkali-unstable epitope (type gamma) in the protein moiety of DIIIa was also characterized as a useful marker of the antigen. However, the type gamma epitope was apparently independent of CASF that was substantially stable to alkali and heat.