Are profilins relevant allergens or confusion allergens?

Advances in the techniques used to study allergic patients have allowed us to recognize multiple mistakes made in the past, and thus to avoid prescribing patient immunotherapy treatments that are not fully valid. One of the major achievements has been the molecular diagnosis of allergic diseases. In effect, while in the past we only had gross determinations of specific IgE to pollens, we can now identify which specific protein triggers the allergic reaction in many of our patients. Moreover, a group of these proteins are known to cluster in panallergen families which exhibit great similarity in their three-dimensional structure, causing the emergence of cross-reactions between the proteins. Several panallergen families have been identified -the profilins being an example of great clinical relevance. Profilins are small proteins with a molecular weight ranging between 12 and 19 kDa, and are present in all eukaryotic organisms, including plants. They participate in numerous biological processes such as cell cytoskeletal reorganization and the regulation of actin polymerization-depolymerization. They likewise intervene in cell structure and mobility, and play a critical role in cell division, embryogenesis and cytokinesis. Unlike plant calcium binding allergens from plants, which are present in most pollens, profilins are part of the storage tissues of plants (fruits, nuts, spices, latex) and, therefore, are also responsible for cross-reactivity between pollens and foods, and even between pollens and latex. Of all cases of cross-reactivity in pollen-food syndrome, profilin sensitization accounts for at least 20%. Profilins have highly preserved sequences, with identities of between 70 and 85% (Ole Bet v2 and Ole e2) and a prevalence of 20% in most patients allergic to pollen. However, there are exceptions such as Chenopodium profilin (Chenopodium album, Che 2), with a reported prevalence of 50% that has caused it to be regarded as the major allergen. Profilin was first described more than three decades ago, with a molecular weight of 15 kDa, joined the monomers and inhibited actin polymerization; as a result, these proteins are named after their property of maintaining profilamentous actin (PRO-FILamentous actIN). Profilins as allergens are found in pollens of Phleum pratense (Phl p 12), Cynodon dactylon (Cyn d 2), Artemisia vulgaris (Art v 4), Zea mays, Triticum aestiviam, Parietaria judaica (Par j 3), Chenopodium album (Che a 2), ambrosia elatior, Olea europaea (Ole e 2), Corylus avellana (2 Cor), Agnus aglutinosa, Castanea sativa, palm (Pho d 2), Mercuriales annua (Mer 1), and also in plant foods such as apple (Mal d 4), peach (Pru p 4), melon (Cuc m 2), watermelon, banana (Mus xp 1), celery (Api g 4), carrot (Dau c 4), hazelnut (Cor a 2), peanut (Ara h 5), cherry (Prop av 4), pear (Pyr c 4), pineapple (Ana c 1), tomato (Lyc e 1), soybean (Gly m 3), pepper (Cap 2) and even latex (Hev b 8). With respect to tree pollens, there is cross-reactivity in families of the order Fagales, including birch, hazel, alder, hornbeam and beech, with their respective allergens Bet v 1, Cor a 1, Aln g 1 and Car b1, for which there is a sequence identity of over 70%. Oleacea is of particular relevance, since Ole e 1 has high sequence identity with homologous allergens: 91% with Fra e1, and 88% and 90% with Lig v1 and v1 Syr. Allergenic plant profilins are highly preserved amino acids sequences. In contrast, non-allergenic profilins from other eukaryotes have lesser identities of close to 30%. One aspect worth noting is that the sequence of the amino and carboxyl terminals of profilins in lower animals, plants and fungi are highly preserved, whereas among vertebrates they are highly divergent. This feature is responsible for the crossreactivity that occurs in this family of panallergens. In northern and central Europe profilins have been identified as one of the four major allergens, because patients allergic to Rosaceae cross-react with birch pollen and/or grasses, with the recognition of specific IgE for profilin in less than 20% of the patients. In Spain sensitization to date palm, a common tree in the Mediterranean region, ranges from 5.6% in Elche to 29.4% in Zaragoza, but this type of pollen has not been found in monosensitized patients -thus suggesting cross-reactivity between pollens. Indeed, palm pollen extracts contain between 25 and 50 times the amount of the grass profilin. It is at this point that mention should be made of the article reviewing ‘‘Profilin sensitization in a Mediterranean