Figure 1. Allergic subjects can be further sub-divided into those with low or high serum-induced basophil responses (‘low basophil responders’ vs ‘high basophil responders’).

(A) Proportion of CD63⁺CRTh2⁺ basophils in response to anti-IgE (5 μg/mL) or grass pollen allergen (Phleum pratense; Phl p) in enriched basophils (left panel, n=3) or PBMCs (right panel; n=6). Basophil activation was evaluated in cells that were left untreated, IgE-stripped with 4% lactic acid or IgE-stripped and resensitized with indicator serum from a grass pollen highly allergic individual (GP IS, grass pollen-specific IgE >100kU_A/L). (B) Concentration-ranging effect of COVID-19 vaccine (BNT162b2), PEG (1 μg/mL) and P80 (1 μg/mL), on CD63⁺CRTh2⁺ basophil activation in enriched basophil or PBMCs. In this validation experiment, we performed this side-by-side basophil vs. PBMC comparison in 5 allergic serum samples using 2 donor basophils. (C) Concentration-ranging effect of COVID-19 vaccine (BNT162b2 or mRNA-1273), PEG and P80 on non-allergics (n=13) and allergics (n=19). (D) Proportion of individuals in the allergic groups who had a reaction within ≤ 5 min, ≤ 20 min or ≤ 120 min. (E) Allergic individuals can be sub-divided into those with low (n=11) or high (n=8) basophil response upon resensitization with serum alone. (F) Unbiased clustering analysis FlowSOM showed differences in metaclusters (MC) 9, 10 and 11 in allergics with low or high basophil response following stimulation with serum alone. FlowSOM was performed on concatenated files. (G) Heatmap representing the expression of CD63, CD203c, C5aR and C3aR in all MC. Blue and red denotes low and high expression, respectively. (H) Population abundance for MC 9, 10 and 11 in allergics with low or high basophil response following stimulation with serum alone, vaccine (15 ug/mL), PEG2000 or P80. Data are presented as mean ± SEM. Violin plots are presented with its media represented in black line. Mann-Whitney U Test, * P<0.05, ** P<0.01.