Features of innate immunity in children and adults

The immune system in the embryonic, neonatal and postnatal periods significantly differs from the immune system in adults. Cytokine gene expression begins during the 10th week of embryogenesis. Production of interferons (IFN) and interleukins (IL) does not exceed 40-50% of the adult level. Phagocytosis occurs from the 12th week of pregnancy. Regulatory T lymphocytes (Treg) amount up to 15% of the CD4+ T lymphocyte population in the embryonic period, after birth their level decreases to 5%, which is typical for adults. In utero immunological tolerance towards own biomolecules and mother's antigens with the suppression of type 1 T-helper (Th1) immune response proinflammatory cytokine production is necessary. At birth, a rapid transition from embryonic tolerance to the binding of innate immunity pattern recognition receptors (PRR) with foreign molecules, primarily mucosal commensal bacteria, results in Th17 cytokine gene expression with the elimination of extracellular pathogens and Th1 immunity inhibition. Repeated stimulation by various exogenous or endogenous factors causes the cytokine gene expression. Trained immunity provides nonspecific resistance of children to pathogens and the protective effect of live attenuated vaccines against various infectious diseases.