Resolving Inflammation: The Impact of Antiretroviral Therapy on Macrophage Traffic In and Out of the CNS.

The effect of antiretroviral therapy (ART) and therapy interruption on myeloid cell traffic out of the central nervous system (CNS) with human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV) infection are understudied. Using intracisternal (i.c.) injection of dual-colored fluorescent superparamagnetic iron oxide nanoparticles (SPION) in SIV-infected macaques early (12-14 dpi) and late (30 days before sacrifice) we studied CNS macrophage viral infection, turnover, and traffic out. SPION are preferentially taken up by perivascular, meningeal, and choroid plexus macrophages. In non-infected macaques, SPION+ macrophages can traffic out of the CNS to the periphery (deep cervical lymph node (dcLN), spleen, and dorsal root ganglia (DRG)), but accumulate in the CNS with SIV infection. ART reduces the accumulation of CNS SPION+ perivascular macrophages but not meningeal or choroid plexus macrophages. ART interruption does not affect the number of SPION+ perivascular and choroid plexus but the number of SPION+ meningeal macrophages increase. ART eliminates SIV-RNA perivascular macrophages, but few scattered RNA+ macrophages in the meninges and choroid plexus remain. With ART interruption, perivascular macrophages remain SIV- but scattered SIV+ meningeal and choroid plexus macrophages exist. In non-infected animals SPION+ macrophages traffic to dcLN, spleen, and DRG at a rate that is decreased with SIV infection and AIDS. SIV-RNA+ SPION+ macrophages that traffic out of the CNS are eliminated by ART and do not rebound with ART interruption. Using two different colored SPION to study the establishment of CNS SIV viral reservoirs, we find greater numbers of early SPION+ macrophages within and outside of the CNS with SIVE, ART, and ART interruption. These data are consistent with SIV-infected perivascular macrophages establishing an early viral reservoir, and continual viral seeding of the meninges and choroid plexus during infection. These findings are consistent with ART reducing traffic of infected macrophages out of the CNS, clearing the CNS perivascular macrophage viral reservoir but not SIV-RNA+ macrophages in meninges and choroid plexus that can rebound with ART interruption.