HLA-DR-positive dendritic cells of the normal human choroid plexus: A potential reservoir of HIV in the central nervous system

In a previous study of the choroid plexus from patients with acquired immunodeficiency syndrome (AIDS), the authors found a population of stromal cells infected with the human immunodeficiency virus (HIV). To determine whether these represented antigen-presenting dendritic cells, the authors examined the phenotype of the normal human choroid plexus with light and electron microscopy and established the HIV-infected cell type with immunohistochemistry in patients with AIDS with an HIV-infected choroid plexus. Monoclonal antibodies were used to detect class II major histocompatibility antigens (MHCs), S-100 and S-lOO protein, lymphocytes, monocyte/macrophage markers, and HIV glycoprotein. A variable number of stromal cells had slightly elongated nuclei and long branching processes that were strongly immunoreactive for class II MHCs, rarely reactive for S-100 and S-100 protein, and immunonegative for monocyte/macrophage markers. Phagocytic activity was absent, as indicated by electron microscopy and immunomarkers. They were numerous in the subepithelial region, and their processes occasionally extended toward the stromal capillaries or between the epithelial cells of the choroid plexus. The HIVinfected cells were intensely immunoreactive for class II MHC markers and often displayed a dendritic morphology. These results document the presence of dendritic cells in the normal human choroid plexus whose morphology and immunophenotype closely resemble those of dendritic cells elsewhere in the body. They also show that these immunoreactive MHC class II cells are the cell type infected by HIV. The authors suggest that the functional activity of the dendritic cells of the choroid plexus is similar to that of antigen-presenting dendritic cells elsewhere in the body. This includes the potential to harbor HIV during the prolonged period of clinical latency, acting as a central nervous system reservoir of infection before the onset of AIDS.