Recombinant reference allergens (Bet v 1.0101, Bet v 1.0102, Aln g 1.0101, Cor a 1.0104, Car b 1.0109 and Que a 1.0301) were produced according to published methods [9 (link), 10 (link)] and characterized physico-chemically [6 (link)]. Endotoxin content was < 0.3 ng/mg for Bet v 1.0101, < 0.3 ng/mL for Bet v 1.0102, < 0.3 ng/mL for Aln g 1.0101, 0.8 ng/mL for Cor a 1.0104, < 0.3 ng/mg for Car b 1.0109, and < 0.3 ng/mg for Que a 1.0301 as determined by limulus amoebocyte lysate (LAL) assay (Associates of Cape Cod, Inc., East Falmouth, MA, USA).