THE IMMUNE SYSTEM OF THE BRAIN AND VIRAL INFECTIONS
The brain is a unique organ with its own local immune system, which is connected with other organs and systems, yet is separated from the systemic circulation by the hematoencephalic barrier, which is differently permeable or impermeable to specific classes of substances. Under systemic or local breakage, hematoencephalic barrier permeability to low ans high molecular weight substances and supramolecular structures and cells increases. Dangerous species entering the brain under such conditions include neuroinfection agents represented by different kinds of microbiota, from viruses to protists. Special roles are played by phagocytes and lymphocytes capable of participating in the classic immune reactions by activating, in particular, complement components, cytokines and other classes of substances. In encephalic tissues, a special role is attributed to microgliocytes, pericytes and macrophages migrating from the blood. Their involvement is especially important upon neuroinfections of various etiologies. During inflammation, astrocytes, oligodendrocytes and neurones involved in brain functions are adversely affected. The role of the hematoencephalic barrier as an obstacle for therapeutic drugs entering into the brain is discussed.