T-Cells and excitotoxicity: HIV-1 and other neurodegenerative disorders.

Until recently the central nervous system (CNS) was considered an immune-privileged site, however, technological and immunological advances have resulted in the CNS being reclassified as an "immune-specialized site." The immune cells, particularly T-cells, continuously patrol the brain and are involved in neuroimmune responses. As such, any changes in the brain microenvironment could affect the physiological functioning of T-cells. Particularly, neurotransmission- associated abnormalities, such as excitotoxicity associated with hypersecretion of glutamate, could severely affect the neuroimmune function of T-cells. Excitotoxicity is involved in the pathogenesis of a number of neurodegenerative disorders. The specific excitotoxicity triggered by the excitatory amino acid neurotransmitter, glutamate, is considered a key mechanism involved in neuronal death. The inability of brain immune cells to overcome these aberrant changes is an active area of investigation. In the systemic circulation, glutamate is inversely related to the number of CD4+ T-cells; however, the effects of elevated glutamate and glutamate-induced exicitotoxicity on cells homing in the brain are critical for understanding neuropathogenesis of neurodegenerative disorders.