Downregulation of CCR5 on brain perivascular macrophages in simian immunodeficiency virus‐infected rhesus macaques

BACKGROUND: C‐C chemokine receptor 5 (CCR5) is a major coreceptor for Human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV) cell entry; however, its role in brain pathogenesis is largely understudied. Thus, we sought to examine cell type‐specific protein expression of CCR5 during SIV infection of the brain. METHODS: We examined occipital cortical tissue from uninfected rhesus macaques and SIV‐infected animals with or without encephalitis using immunohistochemistry and immunofluorescence microscopy to determine the number and distribution of CCR5‐positive cells. RESULTS: An increase in the number of CCR5+ cells in the brain of SIV‐infected animals with encephalitis was accounted for by increased CD3+CD8+ cells expressing CCR5, but not by increased CCR5+ microglia or perivascular macrophages (PVMs), and a concurrent decrease in the percentage of CCR5+ PVMs was observed. Levels of CCR5 and SIV Gag p28 protein expression were examined on a per‐cell basis, and a significant, negative relationship was established indicating decreased CCR5 expression in productively infected cells. While investigating the endocytosis‐mediated CCR5 internalization as a mechanism for CCR5 downregulation, we found that phospho‐ERK1/2, an indicator of clathrin‐mediated endocytosis, was colocalized with infected PVMs and that macrophages from infected animals showed significantly increased expression of clathrin heavy chain 1. CONCLUSIONS: These findings show a shift in CCR5‐positive cell types in the brain during SIV pathogenesis with an increase in the number of CCR5+ CD8 T cells, and downregulated CCR5 expression on infected PVMs, likely through ERK1/2‐driven, clathrin‐mediated endocytosis.