Lymphocytes: potential mediators of postischemic injury and neuroprotection.

Antigen-nonspecific inflammation appears to contribute to postischemic brain injury. Because there is a breach in the integrity of the blood-brain barrier after stroke, the immune system encounters novel central nervous system (CNS) antigens that allow for the development of a CNS antigen-specific autoimmune response. The nature of the immune response generated on antigen encounter is determined by the microenvironment at the site of antigen encounter. For instance, a systemic inflammatory response, such as that which would accompany an infection, could alter the microenvironment in such a way as to promote the initiation of deleterious autoimmunity. If patients who develop an infection in the immediate poststroke period are predisposed toward a CNS autoimmune response, it might help to explain why infection after stroke is associated with increased disability. We present data to support this hypothesis and to show that the breach in the blood-brain barrier can also be capitalized on to modulate the immune response to create a neuroprotective environment after stroke.