Brain because of its functions, is isolated from either external or internal environment. This function is performed by skull, cerebral meninges, cerebrospinal fluid and unique system of mechanisms and barriers restricting exchange of oxygen, soluble substances between blood, nervous tissue and cerebrospinal fluid. Mato cells, located in Virchow-Robin's space play a key role in blood-brain barrier. Mato cells are rich in hydrolytic enzymes. They act as phagocytes in blood-brain barrier by scavenger receptors, which take part in eliminating excess of unfavorable substances from environment. Ageing, hypercholesterolemia and vitamin E deficiency can cause degeneration of perivascular cells and limit their protective function. Mato cells probably are responsible for pathogenesis of various diseases, f.e. Alzheimer disease, diabetic rethinopathy, encephalitis.