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.