Many isoforms of the allergen exist due to polymorphism. They can be classified as isoforms of type A (shown here) and isoforms of type B. A microheterogeneity is detected at positions 4 and 11 of isoforms of type A and at positions 4, 5, 10 and 11 of isoforms of type B. Causes an allergic reaction in human. Allergen from olive pollen. Important in Mediterranean countries and California. Its prevalence is related to the geographic area.