Some common diseases due to immunodeficiency in children (congenital hypogammaglobulinemia, infant transient hypogammaglobulinemia, selective IgA deficiency, congenital thymus dysplasia [DiGeorge’s syndrome], AIDS)
The genesis and development of the human immune system arises in the early embryo, but it is still not completely mature at birth. It develops gradually up to adult level with increasing age. Therefore, in children, especially infants, there is a physiologic hypoimmunity state.
Nonspecific immunity plays a role in the immune system by presenting a physical barrier such as phagocytosis and the complement system which consists of more 20 serum proteins.
Components and characters of nonspecific immunity Thin,damaged easily Physical barrier Skin and mucosa 35-70%of that of adult 60%of content for adult Kill bacteria Complement properdin Low gastric acidity,fail to destroy bacteria,low lactic acid from skin Kill bacteria Tissue fluid:gastric juice,lactic acid from skin Penetration,meningitis,intrauterine infection barrier Blood-brain barrier placental barrier Perfect after 34w GA phagocytosis Macrophage Imperfect,infection diffuse easily Filtration Lymph nodes Characters in children Function Components
The human immune system arises in the embryo from gut-associated tissue. Pluripotential hematopoietic stem cells first appear in the yolk sac at 2.5-3weeks of GA and migrate to the fetal liver at the fifth week of gestation;later they reside in the bone marrow, where they remain throughout life.
Lymphoid stem cells develop from such precursor cells and differentiate into T and B cells. T and B-lymphocytes are the only components of the immune system that have antigen-specific recognition capabilities.
The IgE is associated with immediate hypersensitivity reaction. It exists in small quantities in the circulation.
Through its Fc fragment it binds to tissue mast cells and circulating basophils.
When two IgE molecules bound to these receptors are bridged by an antigen such as ragweed pollen, the cells then can release the mediators characteristic of the allergic response, such as histamine and slow reactive substance of anaphylaxis.(next)
The amount of IgE is also very low in the neonate. It may be obtained from breast milk, and reach to the level of the adult by about 7 years age. IgE is an antibody which bring a type I allergic reaction .