The immunophenotype of perivascular cells in the human brain

The immunophenotype of perivascular cells (PC) in temporal lobe tissues obtained at autopsy in 48 patients (aged 41-88 years) was characterized using light and electron microscopic immunocytochemistry with a variety of antibodies. In all cases studied, PC bearing CD11c (Ki-M1P) and CD68 (KP1) were distributed throughout the temporal cortex. In addition to Ki-M1P and KP1, the monoclonal antibodies against major histocompatibility complex (MHC) class II antigen (Ag) (LN-3, CR3.43), anti-leucocyte common antigen (LCA), LN-5, Mac 387 were all found in PC with variable immunoreactivity. In contrast, LN-1 and OPD4 were not found in PC, although the former showed nearly constant staining of resting microglia. Semiquantitative analysis disclosed differences in the numbers of cells labeled with the markers in the 21 normal brains (Ki-M1P > KP1 >> LCA, LN-3, LN-5 >> Mac 387). Ultrastructurally, immunoreactivity for Ki-M1P, KP1, and LN-3 was observed in PC with cytoplasm containing dense lysosomal bodies. In brains from patients with Alzheimer's type dementia, PC were seen in the wall of beta-amyloid protein-positive small vessels. However, there was no definite alteration of antigenicity in PC from AD brains compared with those from normal brains. The immunophenotype of PC was similar to that of macrophages, which were observed in the perivascular spaces and the leptomeninges in some normal and diseased brains. In contrast with PC, however, macrophages showed high incidence of labeling for some macrophage markers LN-5 and Mac 387. These findings demonstrate that PC may be a normal constituent of the adult human brain with a variable expression of monocyte/macrophages markers and MHC class II Ag and that PC could be distinguished from resting microglia by their morphology and by their immunophenotype.