Basic concepts of immunology and neuroimmunology

The immune system is a complex network of specialized cells and organs that defends the human body against attack from foreign pathogens. The major lymphocytes involved in protecting the body against potential infections are B and T cells, which also play an important role in combating tumor growth. The cells of the immune system patrol the tissues and organs through both blood and lymphatic vessels, but some organs—including cornea, testes, and brain—are usually not patrolled by these cells. The brain has been thought to be an immune-privileged site because of the tight blood–brain barrier (BBB) that protects it. Few cells migrate to the brain under normal circumstances, because the BBB permits only certain molecules to cross into brain tissue. Recently, however, studies have shown that activated T cells exposed to antigen can cross the intact BBB and migrate into brain. This finding opens the path to developing effective means of immunotherapy for lesions of the central nervous system. The authors discu...