Antigenic and allergenic relationships among airborne grass pollens in India

Pollen from grasses (Poaceae) are predominant aeroallergens throughout the world including tropical countries. Studies from USA, Europe, and Australia have shown extensive allergenic/antigenic cross reactivity among the grass pollen allergens prevalent there. No such information is available about airborne grass pollens of tropical countries.

The present study was undertaken to explore common antigenic/allergenic components, if any, of five important grass pollens of India.

Intradermal tests (ID) were performed with pollen extracts of Cenchrus, Cynodon, Imperata, Pennisetum, and Sorghum in patients with nasobronchial allergy. ELISAs were performed for estimating the allergen-specific IgE in sera of patients eliciting markedly positive ID response (2+ to 4+). To detect cross reactivity, ELISA inhibition experiments were carried out using pooled patient sera and five grasses, individually, as inhibitors with different solid phase antigens. To evaluate common antigenic components in Cenchrus, Imperata, and Pennisetum pollen extracts, rocket immunoelectrophoresis (RIE) and ELISA inhibition were conducted using rabbit antisera.

Among 133 patients, Cynodon extract elicited markedly positive skin reactivity in most patients followed by Pennisetum, Imperata, Cenchrus, and Sorghum. A large number of patients showed markedly positive skin reactions and enhanced specific IgE levels to more than one grass pollen extract. ELISA inhibition experiments showed different degrees of cross reactivity among the grass pollens studied. Rocket immunoelectrophoresis and ELISA inhibition using rabbit antisera with homologous and heterologous pollen revealed the presence of shared antigenic components in Cenchrus, Imperata, and Pennisetum extracts.

The varied dose-response curves obtained with ELISA inhibition using different inhibitors suggest the presence of both common and specific antigens/allergens in the grass pollens studied. Based on the extensive immunologic cross reactivity, among the tropical grass species, it may be possible to use mixed allergen preparations for allergy diagnosis and immunotherapy.