The influence of probiotics on immune system development during early childhood: a systematic review

Abstract

Immune system development during early childhood is closely modulated by the colonization of the gut microbiota. Early interaction between commensal bacteria and the gut-associated lymphoid tissue (GALT) is essential for the maturation of both innate and adaptive immune responses, as well as for the establishment of immunological tolerance. Objective of the study was to analyze the current clinical evidence on the influence of probiotic supplementation on the development, maturation, and modulation of the immune system during early childhood, as well as its impact on preventing immune-based pathologies. Systematic review of scientific literature published between 2020 and 2026 in PubMed, Scopus, and Cochrane Library databases. Randomized controlled trials and cohort studies evaluating probiotic administration in infants and children (0-5 years) and measuring immunological biomarkers (e.g., secretory IgA, Th1/Th2/Th17 cytokine profiles) or immune-mediated clinical outcomes were included. The administration of specific strains, predominantly Lactobacillus rhamnosus GG, Bifidobacterium animalis subsp. lactis, and Lactobacillus reuteri, demonstrated a significant induction in intestinal secretory IgA (sIgA) synthesis and a favorable modulation of the Th1/Th2 ratio, thereby reducing pro-allergic polarization. Clinically, a consistent reduction in the incidence and severity of atopic dermatitis was observed in high-risk infants, alongside a significant decrease in the frequency and duration of upper respiratory and gastrointestinal infectious episodes. Probiotic supplementation during early childhood plays a key immunomodulatory role that supports the maturation of the infantile immune system. These findings support its use as a promising therapeutic and preventive strategy against highly prevalent allergic and infectious diseases, though greater standardization regarding strain specificity, dosage, and critical intervention windows is still required.