How far can we simplify in vitro diagnostics for Fagales tree pollen allergy? A study with three whole pollen extracts and purified natural and recombinant allergens.
BACKGROUND
Current diagnostic tests for Fagales tree pollen allergy are often composed of mixtures of pollen of birch, alder and hazel. Their complex composition hampers accurate standardization.


OBJECTIVE
The aim of this study was to investigate whether mixtures of tree pollen extracts can be replaced by a single pollen species, and whether a single pollen species can be replaced by a limited number of purified natural or recombinant major allergens.


METHODS
Sera (n = 1725) were selected on ground of a general suspicion for inhalant allergy, and tested in a RAST for birch, alder and hazel pollen. Sera with > 0.5 RU/mL for any of the three species were tested in a RAST for natural Bet v 1 and Bet v 2 as well as for recombinant versions of both allergens.


RESULTS
Specific IgE antibodies (> 0.3 RU/mL) against birch, alder and hazel were found in 242, 298 and 292 sera, respectively. All sera with a positive RAST for alder and/or hazel and a negative RAST for birch were low-responder sera on alder and hazel, only five sera having a RAST value > 1.0 (all < 2.0). For all sera with a RAST > 0.5 RU/mL (n = 250), the mean of individual ratio's alder/birch and hazel/birch was 1.02 and 0.54, respectively. Of 223 of these sera, 63.2% had specific IgE against natural Bet v 1 and 63.7% against natural Bet v 2. When responses to both allergens were combined 93.7% were positive. The mean ratios Bet v 1 + 2/extract were 1.00, 1.04 and 2. 11 in case of birch, alder and hazel, respectively. For 211 sera the same analysis was performed with recombinant Bet v 1 and Bet v 2. Only six sera with Bet v 1-specific IgE (all < 0.5 RU/mL) were negative (< 0.3 RU/mL) on recombinant Bet v 1. For Bet v 2, 77/132 sera with specific IgE to the natural allergen did not react to the recombinant version. Twelve false-negatives had RAST values > 1.0 RU/mL. The mean of the individual recombinant/natural ratios was 0. 98 for Bet v 1 and 0.38 for Bet v 2 (P < 0.001). The mean ratio rBet v 1 + 2/birch was 0.75 with 17.5% false-negatives on the combination of recombinant allergens.


CONCLUSIONS
Reliable in vitro diagnosis is possible with a single tree pollen extract (birch or alder). The same is true for purified natural Bet v 1 and Bet v 2. A combination of recombinant molecules is slightly less efficient.
Van Ree
R
R
C.L.B., Sanquin Blood Supply Foundation, and the Laboratory for Experimental and Clinical Immunology, Academic Medical Centre, University of Amsterdam, The Netherlands.
Van Leeuwen
W A
WA
Akkerdaas
J H
JH
Aalberse
R C
RC
D000485:Allergens / Q000276:immunology; D052179:Antigens, Plant; D002241:Carbohydrates / Q000276:immunology; D003285:Contractile Proteins; D000939:Epitopes / Q000276:immunology; D006801:Humans; D006967:Hypersensitivity / Q000175:diagnosis*; D007073:Immunoglobulin E / Q000276:immunology; D008840:Microfilament Proteins / Q000276:immunology; D010936:Plant Extracts / Q000276:immunology; D010940:Plant Proteins / Q000276:immunology; D011058:Pollen / Q000737:chemistry / Q000276:immunology*; D051304:Profilins; D011994:Recombinant Proteins; D014197:Trees / Q000276:immunology*
D000485:Allergens; D052179:Antigens, Plant; D002241:Carbohydrates; D003285:Contractile Proteins; D000939:Epitopes; D008840:Microfilament Proteins; D010936:Plant Extracts; D010940:Plant Proteins; D051304:Profilins; D011994:Recombinant Proteins; C061312:Bet v 1 allergen, Betula; D007073:Immunoglobulin E