Profilin & Pan-Allergens

Cross-reactivity is often seen between unrelated species due to shared minor allergens such as Profilin. A minor allergen is an allergenic protein that has demonstrated clinical sensitivity in a minority of patients in a population. Common allergens that demonstrate clinical sensitivity across unrelated species are known as Pan-Allergens.

Profilin is a structual protein that is involved in the construction and maintenance of a cell’s cytoskeleton. It is found in all eukaryotic organisms (e.g. all complex, non-bacterial organisms such as plants and animals).

While it is a common protein found across many organisms, Profilin’s specific structure is more closely related between organisms of the same type (e.g. plants vs. animals). For example, Phl p 12, the Profilin found in Timothy grass, has a protein structure that is over 75% identical to Profilins found in other plants, while it is only 30 – 45% identical to Profilins found in animal cells. It has been estimated that for clinically significant cross-reactivity to exist between molecules, they must be at least 70% identical in structure.

Among similar plant Profilins, it has been shown that Phl p 12 sensitivity can lead to skin test reactivity among unrelated extracts. This suggests that a lot of skin test reactivity may be overestimating the number of clinically significant allergens. If a pan-allergen, such as Profilin, was originally sensitized from grass pollen, then grass may be the most significant allergen and should be the focus of treatment.

Since Timothy grass has significant Major Allergens that would confound results, ALK is evaluating use of Palm Tree extract as a marker of pan-allergen sensitivity. Palm lacks a clinically significant major allergen but contains Profilin (called Pho d 2, for Phoenix dactylifera). This molecule is similar to Profilins found in various grasses, weeds and fruits. It is hypothesized that if a patient reacts to Palm, and demonstrates widespread reactivity across plant species, then he may be exhibiting a Profilin sensitivity that confounds and compounds an underlying grass allergy.