Subtropical grass pollen allergens are important for allergic respiratory diseases in subtropical regions

Abstract

Background: Grass pollen allergens are a major cause of allergic respiratory disease but traditionally prescribing practice for grass pollen allergen-specific immunotherapy has favoured pollen extracts of temperate grasses. Here we aim to compare allergy to subtropical and temperate grass pollens in patients with allergic rhinitis from a subtropical region of Australia.

Methods: Sensitization to pollen extracts of the subtropical Bahia grass (Paspalum notatum), Johnson grass (Sorghum halepense) and Bermuda grass (Cynodon dactylon) as well as the temperate Ryegrass (Lolium perenne) were measured by skin prick in 233 subjects from Brisbane. Grass pollen-specific IgE reactivity was tested by ELISA and cross-inhibition ELISA.

Results: Patients with grass pollen allergy from a subtropical region showed higher skin prick diameters with subtropical Bahia grass and Bermuda grass pollens than with Johnson grass and Ryegrass pollens. IgE reactivity was higher with pollen of Bahia grass than Bermuda grass, Johnson grass and Ryegrass. Patients showed asymmetric cross-inhibition of IgE reactivity with subtropical grass pollens that was not blocked by temperate grass pollen allergens indicating the presence of species-specific IgE binding sites of subtropical grass pollen allergens that are not represented in temperate grass pollens.

Conclusions: Subtropical grass pollens are more important allergen sources than temperate grass pollens for patients from a subtropical region. Targeting allergen-specific immunotherapy to subtropical grass pollen allergens in patients with allergic rhinitis in subtropical regions could improve treatment efficacy thereby reducing the burden of allergic rhinitis and asthma.

Figure 1

Phylogenetic tree of Poaceae grasses with allergenic pollens. Subfamily levels are underlined and clinically relevant species whose pollen investigated herein are coloured.

Figure 2

Inclusion of participants to subject groups. The number recruited to the grass pollen allergic group, other allergies group, or the non-atopic group based on clinical history and skin prick test (SPT) are given. The number in each group from whom plasma was available for IgE testing is given in the next level. A subset of grass pollen-allergic subjects were recalled for IgE cross-reactivity studies.

Figure 3

Allergic sensitization to different grass pollen extracts. A. Average skin prick test diameters for subtropical Bahia, Johnson and Bermuda grass pollens and temperate Ryegrass pollen. Box and whisker plots show median, interquartile range, 10^th and 90^th percentiles and minimal and maximal individual values for data from 48 grass pollen allergic donors from Brisbane. Significant differences by Friedman ANOVA and Dunn's multiple comparison test. B and C. Pairwise data for individual patient sensitivity comparing either Bahia or Bermuda grass pollen with Ryegrass pollen.

Figure 4

Plasma IgE reactivity with pollen of subtropical Bahia, Johnson and Bermuda grasses and temperate Ryegrass pollen. Box and whisker plots show median, interquartile range, 10^th and 90^th percentiles and minimal and maximal individual values for data from 55 grass pollen allergic donors from Brisbane. Significant differences by Friedman ANOVA and Dunn's multiple comparison test. Data on IgE reactivity with Bahia and Ryegrass pollen for 47 of these subjects were published in ref 21.

Figure 5

Cross-inhibition ELISA of serum IgE reactivity with different grass pollen extracts. Serum numbers are given on the top right of each row and the target grass pollen extract with botanical subfamilies are given for each column of graphs. Inhibitors were added to diluted sera from 0.05 to 50 μg/ml (red triangle symbol, Bahia grass; orange inverted triangle symbol, Johnson grass, pink diamond symbol, Bermuda grass, blue square symbol, Ryegrass, light blue circle symbol, Timothy grass and * Peanut extract; a non-grass pollen, allergen control). Data is expressed as the percentage inhibition of uninhibited IgE reactivity with standard errors for three technical replicates shown. The relative avidity of interaction between serum IgE and a target grass pollen is indicated by the maximum level of inhibition achieved with 10 fold excess of pollen inhibitor in solution over target solid-phase pollen allergen, as well as the concentration of pollen inhibitor required to block 50% (IC50; indicated dotted line) of IgE reactivity. Pooled data from four of these donors for inhibition of IgE reactivity with Bahia and Ryegrass pollen was published in reference 21.