Grass pollen allergens globally: the contribution of subtropical grasses to burden of allergic respiratory diseases

Abstract

Grass pollens of the temperate (Pooideae) subfamily and subtropical subfamilies of grasses are major aeroallergen sources worldwide. The subtropical Chloridoideae (e.g. Cynodon dactylon; Bermuda grass) and Panicoideae (e.g. Paspalum notatum; Bahia grass) species are abundant in parts of Africa, India, Asia, Australia and the Americas, where a large and increasing proportion of the world's population abide. These grasses are phylogenetically and ecologically distinct from temperate grasses. With the advent of global warming, it is conceivable that the geographic distribution of subtropical grasses and the contribution of their pollen to the burden of allergic rhinitis and asthma will increase. This review aims to provide a comprehensive synthesis of the current global knowledge of (i) regional variation in allergic sensitivity to subtropical grass pollens, (ii) molecular allergenic components of subtropical grass pollens and (iii) allergic responses to subtropical grass pollen allergens in relevant populations. Patients from subtropical regions of the world show higher allergic sensitivity to grass pollens of Chloridoideae and Panicoideae grasses, than to temperate grass pollens. The group 1 allergens are amongst the allergen components of subtropical grass pollens, but the group 5 allergens, by which temperate grass pollen extracts are standardized for allergen content, appear to be absent from both subfamilies of subtropical grasses. Whilst there are shared allergenic components and antigenic determinants, there are additional clinically relevant subfamily-specific differences, at T- and B-cell levels, between pollen allergens of subtropical and temperate grasses. Differential immune recognition of subtropical grass pollens is likely to impact upon the efficacy of allergen immunotherapy of patients who are primarily sensitized to subtropical grass pollens. The literature reviewed herein highlights the clinical need to standardize allergen preparations for both types of subtropical grass pollens to achieve optimal diagnosis and treatment of patients with allergic respiratory disease in subtropical regions of the world.

Relevance of Allergenic Sensitization to Cynodon dactylon and Phragmites communis: Cross-reactivity With Pooideae Grasses

“…Two patients (#12 and #14 in Table 1) had high sIgE to Phl p 1 but negative results for Cyn d 1. This observation confirms previous reports of immunologic differences between the 2 allergens [17] in terms of recognition of T-cell epitopes [21,22] and in amino acid sequence and 3D structure [13]. In addition, the correlation coefficient (R 2 ) between Phl p 1 and Cyn d 1 sIgE values was 0.5, corroborating the presence of different IgE binding epitopes.…”

“…Our findings are consistent with the fact that GM is the primary sensitizer in the study population. Asymmetric cross-reactivity between temperate and subtropical grasses has been reported [21] and varies according to the geographic origin of patients.…”

“…However, there are other subfamilies with species capable of inducing allergic symptoms, such as Chloridoideae (Cynodon dactylon) and Arundinoideae (Phragmites communis). Both C dactylon and P communis have been identified in warm temperate and subtropical areas in Africa, Asia, Australia, and America [1], and also in Europe up to a latitude of approximately 53°N [2]. Although C dactylon is now cosmopolitan, it is generally recognized that its present distribution is largely due to human activities [3] as it is used as livestock herbage and turf.…”

“…C dactylon has been found to flower later than temperate grasses [6], possibly explaining the onset of symptoms in grass-sensitized patients in late June or July. Patterns of sensitization depend on primary grass sensitization and differ from one geographic region to the next [1].…”

“…Moreover, group 1 allergens in C dactylon have different epitopes to group 1 allergens in Pooideae grasses [1,17]. These differences are probably responsible for the low cross-reactivity between C dactylon and members of the Pooideae subfamily [1,18].…”