IGHE and Allergy: PC2 (genus level) shows association with atopic sensitization (Figure 4A) and it is nearly perfectly described by the abundance of bifidobacteria minus the abundances of Bacteroides and E. coli at 3 months of age (p < 0.001, rs = 0.96), which further shows an inverse association with atopic sensitization (Figure 4B) and represents a clear vector associated with the number of allergen-specific IgEs (p = 0.012), the age of the first allergen-specific IgE (p = 0.039) and also the diagnosis of allergies (p = 0.012).