Brain development and the immune system: an introduction to inflammatory and infectious diseases of the child's brain

A short overview of the specificities of immune response within the brain is given as an introduction to subsequent chapters on infectious and inflammatory diseases of the child's brain. The blood-brain barrier starts developing during vascular proliferation of the developing brain during neurogenesis but maturation is not completed until several weeks after birth, and varies in different parts of the brain. The development of postcapillary venules in which cell recruitment occurs seems to be completed at birth. Brain macrophages are detected in brain tissue from the 8th to 12th week of gestation and then exert an important role during neuroblast selection and differentiation, as astrocytes and macrophages acquire the ability to secrete soluble substances. From the third trimester, the fetal brain is able to generate an inflammatory reaction and toll-like receptors can be detected on the surface of fetal neurons and glial cells. Innate immunity maturation occurs within weeks after birth. Although neonates lack preexisting immunological memory and have a small number of immune cells in peripheral lymphoid tissues, they are competent to develop a mature T-cell response, they have a strong CD8 cytotoxic function, and dendritic cells are fully competent.