[Immune reactions in the brain]

The immunological status of the brain is generally presented as an "immune privileged" site because of the presence of a strong blood-brain barrier, the lack of lymphatic drainage and, as for the eye, the paucity of professional antigen-presenting cells. This dogma is now challenged by recent studies indicating that there is an active communication with the immune system and that presentation of endogenous (as in autoimmune encephalomyelitis) or exogenous (like in neurocysticercosis or toxoplasmosis) antigens occurs. The local immune (cell-mediated and non-inflammatory humoral) responses seem regulated by active immunosuppressive mechanisms, including apoptosis of alloreactive lymphocytes, in order to limit the destructive effect of inflammatory reactions in this fragile tissue.