Mechanisms Protecting Against Infection Development
Protection against infection involves two cooperating systems—innate (natural) immunity and acquired (adaptive) immunity. Both are essential to defend the child's body against persistent threats from pathogenic microorganisms.
Innate Immunity
Innate (non-specific) immunity is provided by the skin and mucous membranes, forming an effective barrier against most microorganisms. Very few infectious agents penetrate through intact skin; however, some can enter the body via the mucous membranes of the respiratory, urinary, or digestive tracts. Others can cause infection if they enter directly into the bloodstream.
All non-specific defense mechanisms are less developed the younger the child. Full immunity is only achieved by the end of the second year of life. The natural immaturity of defense mechanisms in children facilitates the development of infections. The skin of newborns and infants is delicate, prone to injury, and characterized by structural and physiological immaturity, which makes it easier for bacteria to penetrate into deeper tissues. Even minor mechanical or chemical damages, as well as opened sweat gland outlets, can lead to local skin infections, which may then spread via the bloodstream causing systemic infection, i.e., sepsis.
Acquired (Adaptive) Immunity
Acquired (specific) immunity is determined by closely cooperating, specific cells of the immune system—antibodies (immunoglobulins). This type of immunity is also the least developed in young children. In the neonatal period, the blood serum of the newborn contains only maternal antibodies, passing through the placenta. The remaining antibodies are received through maternal breast milk.
Premature infants have reduced infectious resistance. They receive a relatively shorter period of maternal antibody transfer via the placenta, and their other immune response mechanisms are significantly less mature.
Newborn begins producing its own immunoglobulins after birth, reaching about 60% of adult levels by around 12 months of age. At the same time, maternal immunity antibodies in the infant’s blood start gradually declining, disappearing completely around 9 months of age. At about 3 months, the antibody level is at its lowest because most maternal antibodies are destroyed by natural breakdown, and the infant's own production is still weak.
During this time, signs of temporary immune deficiency may appear, resulting in increased susceptibility to viral, bacterial, or fungal infections. The poor immunity of the newborn is related not only to the immaturity of the immune system but also to the sterility of its environment, as intrauterine conditions are largely free from external factors that are necessary for immune system development.
Immunity Grows with Age
Full functional maturity of the child's immune system gradually develops over time. The growth rate varies depending on exposure to external factors, genetic and environmental conditions, nutritional deficiencies, and other factors. Generally, a sufficient immune response is considered to develop around the age of 7.
Disorders in the functioning of the gradually maturing immune system in children can manifest as severe infections and, in combination with harmful external factors, reveal diseases of systemic or neoplastic nature.
Human body constantly adapts to changes related to different life stages, environmental influences, and lifestyle. Aging, stress, intense physical activity, climate conditions, and nutritional deficiencies are just some factors that weaken immune system functioning. Conversely, maintaining good overall health through a healthy lifestyle and a properly balanced diet also supports the correct immune response to external harmful factors.
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