Grass pollen allergy
Grass pollen allergy is probably the most studied allergic pathology. There is a broad allergen panel for CRD of grass allergy, and a SLIT AIT product that is the only one with a complete clinical program, including several five-years studies,12 that provides the best available information to understand the link between sensitization profiles and AIT.
Allergen composition studies of a Phleum pollen extract34 allowed to establish that Phl p 5 and its related allergen Phl p 6 are the most abundant proteins, accounting for more of 50% of protein content. Accumulated content of Phl p 1 represents less than 10%. The rest of allergen components are in a range from 1-10% of total protein. Despite the relatively low abundance, Phl p 1 is the most relevant single allergen sensitizer of grass allergic patients. Epidemiological studies performed in Spain35,36and CRD analysis of 1905 patients included in AIT clinical trials of grass pollen allergy in North America27 demonstrated the preponderance of Phl p1 as primary sensitizer to grass pollen. In fact, a significant proportion of patients were mono sensitized to this allergen. Similar results in pediatric grass allergen patients have been reported 37.
Recently a potential explanation for this has been published38. Group 1 grass allergens, belonging to the beta expansins family, are present in other plant parts. In Autumn, upon plant death, plant particles are aerosolized and might be presented together with Alternaria spores, initiating sensitization process. No loss of effect in AIT is observed in patients mono-sensitized to either Phl p 1 or Phl p 527; however, patients with low (first tercile) sIgE to any of the two major allergens presented no clinical benefit in the first pollen treatment season. As we have already mentioned, early effect is governed by desensitization in a dose-dependent manner. Patients with low sIgE levels might need a higher allergen dose to get desensitized; however, in a five-year mechanistic study 9, an impaired regulatory response for this type of patients was not observed, and thus they should not be excluded for AIT if they meet clinical inclusion criteria.