Background: 15-30% of patients infected with HIV will develop a debilitating dementia. Whilst HIV enters the brain soon after infection, presumably within monocyte-derived macrophages, not all patients with HIV become demented. Blood monocytes probably cross the blood-brain barrier and give rise ultimately to parenchyma macrophages. We looked for a specific monocyte subset in AIDS patients with dementia.
Methods: Peripheral blood monocytes from three groups were compared: AIDS patients with (n = 12) and without (n = 11) dementia, and ten HIV seronegative healthy controls. We used flow cytometry to analyse monocytes, and cell lysis and apoptosis assays to examine monocyte effects on human brain cells in vitro.
Findings: We found a unique subset of monocytes in patients with AIDS dementia. These monocytes were more dense and granular and expressed CD14/CD16 and CD14/CD69. Means (SD) for CD14/CD16 in HIV-negative controls and in AIDS non-dementia and AIDS dementia patients were 6.5% (4), 16% (13), and 37% (21), respectively (p = 0.008 between the two groups of patients). The corresponding means for CD14/CD69 were 7% (6), 8% (10), and 69% (18) (p < 0.0001).
Interpretation: CD69 is a member of the natural-killer-cell gene complex that is expressed after activation. Supernatants from cultures containing these dense cells can trigger apoptosis of human brain cells in vitro. The monocyte subset we found in patients with AIDS dementia might enter the brain and expose neural cells to toxic factors.