For a study, researchers sought to see how PPOIT (Probiotic and Peanut Oral Immunotherapy) affected peanut-specific humoral immunological indices and how such longitudinal indices were related to SU (sustained unresponsiveness) persistence. Peanut component- and whole-peanut serum/plasma levels throughout time (Ara-h1, -h2, -h3, -h8, -h9) ImmunoCAP was used to quantify specific-IgE (sIgE) and specific-IgG4 (sIgG4) antibodies, and salivary peanut-specific-IgA (sIgA) was quantified by ELISA in children (n=62) enrolled in the PPOIT-001 randomised study from baseline (T0) to 4 years after treatment (T5). Multivariate regression analysis using log-transformed values was performed for point-in-time comparisons between groups. Generalized estimating equations (GEE) were used for longitudinal comparisons between groups. Oral immunotherapy with probiotics and peanuts was linked to changes in sIgE and sIgG4 levels over time. Post-treatment, sIgE levels were considerably lower [T5, PPOIT vs Placebo geometric mean (GM) ratio: Ara-h1 0.07, P=.008; Ara-h2 0.08, P=.007; Ara-h3 0.15, P=.021]. End-of-treatment sIgG4 levels were considerably higher (T1, PPOIT vs. Placebo GM ratio: Ara-h1 3.77, P=.011; Ara-h2 17.97, P<.001; Ara-h3 10.42, P<.001), but levels in the PPOIT group dropped once treatment was ended and reverted to levels equivalent to the Placebo group by T5. Similarly, salivary peanut sIgA increased during treatment (PPOIT vs. Placebo, the ratio of GM: 2.04, P=.014), then decreased after treatment (PPOIT vs. Placebo, the ratio of GM: 2.04, P=.014). Peanut butter and probiotics Oral immunotherapy was linked to a significant decrease in peanut-specific humoral responses, suggesting that it might mediate the clinical benefits of SU that last for up to 4 years after treatment.