Immune response to retroviral infections of the brain.

Various neurological manifestations of retroviral infections have been reported, including peripheral neuropathy, encephalopathy and neuronal degeneration. After penetration into the central nervous system (CNS) the invading retroviruses meet a unique immunological situation that differs significantly from that in the periphery. Due to the blood-brain barrier with its general access restrictions peripheral T-cells, monocytes and B-cells are only "guests" in the brain; instead the immune balance is shifted in favour of the local innate immunity with microglia, astrocytes, cytokines/chemokines and complement forming the dominating defence network. The present article focuses on the most important retroviral infections and highlights the immunological aspects of the neuropathogenesis induced by selected retroviruses. These aspects include: (i) local and infiltrated immune cells as targets of retroviral infection; (ii) stimulation of the cerebral immunity network by retroviruses and subsequent steps of antiviral defence; and (iii) immune activation products as potential contributors to neural damage in the sensitive brain tissue.