E extent of immune activation in both blood and the brain and correlates with systemic and neurological disease status [17,53,55-59]. During immune activation, particularly while levels of IFN-g are increased, induction of the enzyme indoleamine 2,3-dioxygenase occurs, increasing the synthesis of QUIN [53,62-64]. HIV-infected microglia also release chemokines [65], which may enhance infiltration a