CHARACTERISTICS OF CHILDHOOD IMMUNITY
The human immune system begins to form before the birth of a child. Its place and extent of health effects are genetically programmed. From birth to puberty, step by step, the structure and functions of the immune system are formed. The development of the immune system is undergoing a number of critical stages that must be taken into account when assessing the state of health, the formation of preventive programs and the appointment of treatment for diseases. The main cell of the immune system is a lymphocyte. In addition, tissue macrophages, neutrophils, and natural killers (ECs) also participate in providing an immune response. The development of the body’s immune system continues throughout the entire period of childhood. In the process of development of the child’s immune system, “critical” periods are distinguished, i.e. periods of maximum risk of developing infectious diseases associated with insufficient immune system functions. Allocate innate and acquired immunity. Innate immunity is provided by factors of natural resistance. Some mechanisms of the fight against infection are innate, that is, they are present in the body before meeting with any infectious agent and their activity does not depend on a previous meeting with microorganisms. The main external protective barrier that prevents the penetration of microorganisms into the human body is the skin and mucous membranes. The protective properties of the skin are, first of all, its impermeability (physical barrier) and the presence of microorganism inhibitors on the surface (lactic acid and fatty acids in sweat and sebum secretion, low pH on the surface). To understand the functional capabilities of the immunity of a growing organism, it is important to know the physiology of its formation, which is characterized by the presence of five critical periods of development.
The first critical period is up to 28 days of life, the second – up to 4-6 months, the third – up to 2 years, the fourth – up to 4-6 years, the fifth – up to 12-15 years.
The first critical period is characterized by the fact that the child’s immune system is suppressed. Immunity is passive in nature and is provided by maternal antibodies. At the same time, its own immune system is in a state of suppression. The phagocytosis system is not developed. The newborn shows little resistance to opportunistic, pyogenic, gram-negative flora. A tendency to generalization of microbial-inflammatory processes, to septic conditions is characteristic. The child is very sensitive to viral infections, against which he is not protected by maternal antibodies. Approximately on the 5th day of life, the first cross in the white blood formula takes place and the absolute and relative predominance of lymphocytes is established.
The second critical period is due to the destruction of maternal antibodies. The primary immune response to infection penetrates through the synthesis of class M immunoglobulins and leaves no immunological memory. This type of immune response also occurs with vaccination against infectious diseases, and only revaccination forms a secondary immune response with the production of antibodies of the IgG class. The insufficiency of the local immunity system is manifested by repeated SARS, intestinal infections and dysbiosis, skin diseases. Children are very sensitive to respiratory syncytial virus, rotavirus, parainfluenza viruses, adenoviruses (high susceptibility to inflammatory processes of the respiratory system, intestinal infections). Pertussis and measles occur atypically without leaving immunity. Many hereditary diseases, including primary immunodeficiencies, make their debut. The frequency of food allergies is sharply increasing, masking atopic manifestations in children.
The third critical period. The child’s contacts with the outside world are expanding significantly (freedom of movement, socialization). The primary immune response (IgM synthesis) to many antigens is maintained. At the same time, the switching of immune responses to the formation of antibodies of the IgG class begins. The local immunity system remains immature. Therefore, children remain susceptible to viral and microbial infections. During this period, for the first time, many primary immunodeficiencies, autoimmune and immunocomplex diseases (glomerulonephritis, vasculitis, etc.) are manifested. Children are prone to repeated viral and microbial inflammatory diseases of the respiratory system, ENT organs. The signs of immunodiathesis (atopic, lymphatic, autoallergic) become more clear. Manifestations of food allergies are gradually weakening. According to immunobiological characteristics, a significant part of children of the second year of life is not ready for the conditions of stay in the children’s team.
The fourth critical period is characterized in that the average concentration of IgG and IgM in the blood corresponds to the level of adults, however, the level of IgA in the blood still does not reach the final values. The IgE content in blood plasma is characterized by a maximum level in comparison with other age periods, which is partly due to the rather frequent parasitic infections during this period.