The role of pan-allergens
An interesting subgroup of grass pollen allergic patients are sensitized to profilin, a pan-allergen present in all vegetable tissues, with a highly conserved structure. Usually, profilin is a confounding diagnostic factor, which is minimized by CRD diagnosis either “in vitro” or even “in vivo”39. Profilin sensitization strongly associates with grass pollen allergy35 in base to a relatively high profilin content in grass pollen compared to other pollens 40. Usually, sensitized profilin patients present no food-mediated reaction or only local (oral) ones. However, in areas of very high grass pollen exposure, some allergic patients do not respond to AIT and present severe food profilin-mediated reactions41,42. In fact, T cell reactivity to profilin increases along with grass pollen intensity exposure. Moreover, in patients from central Spain, T cell proliferation induced by profilin is similar to that induced by the major allergen Phl p 134. These peculiar patients, as well as others exposed to very high pollen levels, can be identified by combining CRD with clinical evaluation and provide invaluable models to understand allergic inflammation and AIT mechanisms and its limitations.
Finally, patients sensitized simultaneously to the pollen pan-allergens polcalcin and profilin have been shown to have twice as many primary sensitizations and to duplicate as well allergy disease evolution time36, suggesting that AIT might not be effective. Similar results supporting clinical value for Phl p 7 and Phl p 12 have been described in pediatric cohorts37.Moreover, this specific double sensitization profile to pan-allergens is not linked to any particular pollen36. At this moment other grass allergens present a limited diagnostic value for AIT decisions and some of them provide confounding information due to lack of specificity 43.
Figure 1 represents an algorithm to support decision-making in the selection of AIT for grass pollen allergy.