Humoral immunity involves the production of antibodies (immunoglobulins). In children up to 2-3 months of age, most humoral immunity is IgG antibodies obtained from the mother during pregnancy. Maternal antibodies begin to disappear between 2 and 6 months of age. An increase in the production of the child's own immunoglobulins is observed from 6 months of age.

If the child's synthesis of immunoglobulins is too low, as the antibodies received from the mother disappear from the body, the number of infections increases and they become more severe. Other immunoglobulins (IgM, IgA and IgE) are not transported across the placenta and their synthesis begins after birth.

Immunoglobulin A reaches adult values at the latest (only at 8-12 years of age). Cell-mediated immunity (dependent on T lymphocytes) is formed from birth until the age of 6 years, when NK cells ("natural killer" cells) become fully active. It is important to realise that almost every child falls ill more often than an adult because the capacity of their immune mechanisms is low.

It is estimated that the immunity of a 3-month-old infant is only 15% of that of an adult. Even at the age of 2-3 years, a child's immunity can be approximated as about 30% of that of an adult. The immune response increases slowly with age, and only reaches a level comparable to that of an adult immunity in the 12-15 age range! It is therefore understandable that the majority of children in the first years of life fall ill very frequently, especially in autumn and winter and especially when children are in larger groups (nurseries, kindergartens) where viral infections spread very easily.

In our climatic zone, even children with properly functioning immune mechanisms fall ill an average of 6-8 times a year. Infections mainly affect the respiratory tract and their course is usually mild. In the periods between infections, children are healthy.

This clinical picture should not raise suspicion of immunodeficiency disorders. In children with immunodeficiencies, the frequency and course of infections are different. The European Immunodeficiency Society (EISD) and international patient organisations (Jeffery Modell Foundation and IPPUMP) have agreed on a list of 10 worrying signs that may indicate primary immunodeficiency.

One or more of the following 10 symptoms indicate the need to undertake a detailed examination of the immune system in Level II reference centres: in provincial and district immunology or paediatric wards and clinics, or in Level III reference centres in regional and inter-regional centres. Symptoms of concern include:

• eight or more ear infections per year
• two or more sinus infections per year
• uninterrupted antibiotic therapy for two months or more with little clinical improvement
• two or more pneumonias in one year
• lack of weight gain or stunted growth
• repeated deep skin or organ abscesses
• chronic oral or skin ulcers in children after the first year of life
• need for treatment of infections with intravenous antibiotics
• a history of two or more serious infections, such as encephalitis, osteomyelitis, dermatitis or septicaemia
• a family history of primary immunodeficiency

There is no home treatment. In cases of established congenital immunodeficiency, systematic administration of intravenous immunoglobulin preparations is necessary in certain cases. Prophylactic administration of antibiotics and antifungal drugs is sometimes necessary. A bone marrow transplant may be the last resort.