Ozone　(O-3)　and　nitrogen　dioxide　(NO2)　are　thought　to　play　primary　roles　in　aggravating　air　pollution　induced　health　problems.　However,　the　effects　of　joint　O-3/NO2　on　the　allergenicity　of　pollen　allergens　are　unclear.　Humulus　japonicus　pollen　allergen　1　(Hum　j1)　is　a　profilin　protein　that　causes　widespread　pollinosis　in　eastern　Asia.　In　order　to　study　the　effects　of　combined　O-3/NO2　on　the　allergenicity　of　Hum　j1,　tandem　six-histidine　peptide　tag　(His6)-fused　recombinant　Hum　j1　(rHum　j1)　was　expressed　in　a　prokaryotic　system　and　purified　through　His6　affinity　chromatography.　The　purified　rHum　j1　was　used　to　immunize　SD　rats.　Rat　sera　with　high　titers　of　IgG　and　IgE　antibodies　against　rHum　j1　were　used　for　allergenicity　quantification.　The　rHum　j1　was　exposed　to　O-3/NO2,　and　changes　in　allergenicity　of　the　exposed　rHum　j1　were　assayed　using　the　immunized　rat　antibodies.　Tandem　LC-MS/LC　(liquid　chromatography-mass　spectrometer/liquid　chromatography　spectrometer)　chromatography　and　UV　and　circular　dichroism　(CD)　spectroscopy　were　used　to　study　the　structural　changes　in　rHum　j1.　Our　data　demonstrated　that　a　novel　disulfide　bond　between　the　sulfhydryl　groups　of　two　neighboring　cysteine　molecules　was　formed　after　the　rHum　j1　exposure　to　joint　O-3/NO2,　and　therefore　IgE-binding　affinity　was　increased　and　the　allergenicity　was　reinforced.　Our　results　provided　clues　to　elucidate　the　mechanism　behind　air　pollution-induced　increase　in　pollinosis　prevalence.　(C)　2017　Elsevier　Ltd.　All　rights　reserved.