Allergenic relationship among four common and dominant airborne palm pollen grains from Eastern India

BACKGROUND: Palm pollen grains are predominant aeroallergens in the tropics including India. Evidence of allergenic crossreactivity had been reported from various parts of the world on different families, e.g. Poaceae, Asteraceae, etc. No such information is available about the palm pollen of tropical countries. OBJECTIVES: The present study was undertaken to find out the allergenic relationship, if any, in four common and important palm pollen in India. METHODS: A 2-year aerobiological survey was carried out at Madhyamgram situated at the suburban fringe of Calcutta Metropolis using Burkard volumetric sampler to know the seasonal variation of Areca catechu, Borassus flabellifer, Cocos nucifera and Phoenix sylvestris among others. Skin-prick tests (SPT) were performed with the relevant pollen extracts on the respiratory allergic patients. Sera from the subjects were tested directly by ELISA for estimating the allergen specific IgE. ELISA inhibitions and dot blotting were performed with pooled patients sera and four palm pollen extracts to detect the cross-reactivity. RESULTS: Among 70 patients, Areca catechu exhibited the maximum percentage (48.5%) of positive responses followed by Cocos nucifera (45.7%), Phoenix sylvestris (42.85%) and Borassus flabellifer (38.5%). On an average, 30-50% of the patients showed positive skin reactions and enhanced specific IgE level to more than one palm pollen extract. Further evidence of allergenic crossreactivity among the four palm pollen grains were provided by dot blotting and ELISA inhibition studies. In ELISA inhibition, a distinct inhibition was obtained with comparable amounts of the pollen extracts. CONCLUSION: The suburban aerobiological survey of Calcutta and SPT results confirmed that the relevant pollen types are significant contributors of aeroallergen load of the study area. ELISA inhibition studies with the pooled patients sera using antihuman IgE probe revealed the presence of shared allergenic components among the four palm pollen grains.