This article presents a review of modern Russian and foreign literature on anti-infective resistance in frequently ill children. Specific immunity issues of acute respiratory diseases in children with allergic reactions are discussed. Immunity protection levels, mechanisms of congenital and acquired immunity are described as well as the role of T-helpers (Th1-, Th2-) imbalance in allergy in children. The role of CD4⁺ T-cells subpopulations — natural (nTreg) and adaptive (iTreg) regulatory T-lympho- cytes — in the immune response pathogenesis is discussed. A detailed description of natural regulatory T-lymphocytes subpopulation and their transcription factor FOXP3 is given. Data on nTreg ability to suppress activity of both Th1-cells and Th2-cells is included. Further studies of regulation of T-cells differentiation and its role in homeostatic recovery of immunity in frequently ill children are underlined.