It is conceivable that, when allergen is introduced early as a method of prevention of food allergy, the same blocking mechanism of IgG4 contributes to reduced IgE-antigen crosslinking, reduced type 2 cytokine production by CD4+ T cells, and reduced production of IgE, thus facilitating a state of tolerance that persists even when IgG4 levels decline after prolonged consumption or cessation of antigen exposure, as seen at 72 months in the LEAP trial. Here, CD4 is linked to food allergy.