High‐affinity Bet v 1‐specific secretory IgA antibodies in nasal fluids protect against birch pollen allergy

low- affinity SIgA. As NAs were shown to possess more high- affinity SIgA, such an effect was absent. Here, we first-time demonstrate that healthy individuals exposed to birch pollen mount a distinct nasal fluid antibody repertoire toward Bet v 1. Functional high- affinity SIgA in NA was identified as protective factor that can prevent allergic sensitization through efficient allergen capture in the nasal mucosa. Further studies will reveal the potential of SIgA as diagnostic marker to discriminate allergic and atopic individuals and to monitor the success of allergen- specific


S U PP O RTI N G I N FO R M ATI O N
Additional supporting information may be found online in the Supporting Information section. DOI: 10.1111/all.14782 High-affinity Bet v 1-specific secretory IgA antibodies in nasal fluids protect against birch pollen allergy To the Editor, Nasal fluid antibodies act as specific barrier molecules against inhaled antigens through neutralization and shielding mechanisms.
They comprise (i) the most abundant and locally produced dimeric secretory IgA (SIgA), (ii) pentameric secretory IgM (SIgM), and (iii) monomeric IgG from passive leakage through blood. 1 The few allergy studies on nasal fluid antibody subclasses showed divergent results regarding quantification of total or allergen-specific reactivities. [2][3][4] So far, comprehensive profiling of antibody subclasses combined with functionality tests is lacking.
In this study, ten non-allergics (NA) and ten birch pollen allergics (BPA) from Austria were recruited (Ethics Commission Land Salzburg, 01/20/2011). NA were free of allergy symptoms and IgE negative to birch pollen and Bet v 1 (Table 1). BPA suffered from rhinitis/rhino-conjunctivitis, and two patients also presented with asthma. BPA were SPT-positive to birch pollen with medium/high serum IgE levels to birch pollen (mean = 21.8 kU/L) and Bet v 1 (mean = 23.2 kU/L) ( Figure E1).
Using nasal fluids from NA and BPA obtained immediately after the birch pollen season, antibody subclass reactivity to Bet v 1 was determined ( Figure 1A). Bet v 1-specific IgE in nasal fluids of BPA was generally low due to the mild sampling technique, but patients with high serum IgE also showed elevated levels in nasal fluids (Table E1). Interestingly, BPA showed significantly higher nasal fluid IgG4 (p < 0.001) and IgG (p < 0.01) compared to NA. This observation is a consequence of elevated serum IgG4 that accompanies IgE production in allergics, as nasal fluid IgG is not produced locally but originates from serum transudation. 5,6 Indeed, Bet v 1-specifc IgG was also higher in serum of BPAs and correlated well with serum IgG (Table E1). High Bet v 1-specific SIgA and moderate SIgM reactivity was observed, revealing no difference between NA and BPA ( Figure 1A). Interestingly, complete nasal fluids of BPA lacked efficient blocking activity despite the fact that purified IgG showed some inhibitory capacity ( Figure 1E). Solely in allergics, an interplay of mucosal antibody subclass interaction led to outcompeting of allergen-IgG binding by the high abundance of low-affinity SIgA.
This bound SIgA might however in turn elute off during ELISA wash steps or, more likely, high-affinity allergen-specific serum IgE displaces the low-affinity SIgA. As NAs were shown to possess more high-affinity SIgA, such an effect was absent. Here, we firsttime demonstrate that healthy individuals exposed to birch pollen mount a distinct nasal fluid antibody repertoire toward Bet v 1.
Functional high-affinity SIgA in NA was identified as protective factor that can prevent allergic sensitization through efficient allergen capture in the nasal mucosa. Further studies will reveal the potential of SIgA as diagnostic marker to discriminate allergic and atopic individuals and to monitor the success of allergen-specific immunotherapy.

K E Y WO R DS
allergens and epitopes, allergy diagnosis, immunologic tests, mucosal immunity, pollen

FU ND IN G INFO R M ATI O N
The study was funded by the Austrian Science Fund (FWF) project P26125.  We measured ASM contraction using organ baths. Both C48/80

CO N FLI C T O F I NTE R E S T
and HDM induced marked constriction in trachea from sensitized guinea pigs (Figure 1). The effects of HDM were most likely due to specific IgG which, in addition to IgE, has been shown to induce smooth muscle contractions in guinea pig trachea 3 ( Figure S1).
Antagonizing histamine H 1 receptors inhibited the concentrationresponse curves and the initial 15 minutes of responses induced by submaximal bolus dose challenges, indicating that the early response of both treatments was mediated by histamine. In contrast, the whole phase responses could only be dampened by inhibition of both histamine and 5-lipoxygenase (5-LOX) pathways, suggesting that both C48/80 and HDM contractions were mediated through histamine and 5-LOX products (Figure 1).
For measuring mediator release induced by C48/80 and HDM, a bolus dose of the strongest concentration of each stimulus was given.
Histamine and lipid mediators in the bath fluids were measured by ELISA and a recently developed mass-spectrometry platform with high specificity and sensitivity for detecting lipid mediators. 4 Both C48/80 and HDM released histamine to similar levels ( Figure 2). In addition, 29 lipid mediators were changed after 60 minutes stimulation; 15 were elevated by both C48/80 and HDM challenge, and an additional 13 only by C48/80, while LTE 4 was only elevated by HDM ( Figure S2 and Table S1).
The prostanoids were the most abundant bioactive lipid mediators detected in the organ baths after challenges. Prostaglandin (PG) D 2 , a major lipid mediator from MCs, together with PGD 1 and PGD 3 , were elevated in bath fluids challenged by C48/80 and HDM to similar levels. On the other hand, thromboxane (TX) B 2 , was to a greater extent released by C48/80 than HDM, and PGE metabolites, PGF 2α , 6-keto-PGF 1α , and TXB 3 were solely increased by C48/80 (Figure 2 and Figure S3).
Both C48/80 and HDM increased LTB 4 , whereas only HDM triggered the release of cysteinyl leukotrienes (CysLTs) reflected by the elevation of LTE 4 (LTC 4 0%, LTD 4 1.7%, and LTE 4 98.3% of measured products by an additional analysis). In addition to prostanoids and leukotrienes, low levels of other lipid mediators were primarily increased by C48/80 (Figure 2 and Figure S3).
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