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.