BackgroundAIDS-related non-Hodgkin's lymphoma (NHL) includes systemic lymphomas, often with brain involvement, and primary central nervous system (CNS) lymphomas.ObjectiveTo examine if measurement of soluble CD23 (sCD23) in cerebrospinal fluid (CSF) is useful in the diagnosis and follow-up of AIDS-related NHL.MethodsCD23 was measured by enzyme-linked immunosorbent assay and EBV DNA by nested polymerase chain reaction for a group of 134 patients. The NHL group included 14 patients with primary HIV-1 CNS lymphoma, 12 patients with brain involvement of systemic HIV-1 NHL and 10 patients with systemic HIV-1 NHL without brain involvement. These were compared with HIV-1-infected patients with cerebral toxoplasmosis (19), progressive multifocal leukoencephalitis (PML; 8) and AIDS-related dementia (17) and with asymptomatic HIV-1 carriers (54) and uninfected individuals (50). The levels of sCD23 were compared with the presence of Epstein–Barr virus (EBV) DNA in CSF.ResultsSignificantly higher levels of sCD23 were found in the CSF of the patients with brain lymphoma than in those with systemic NHL (P< 0.002) or with cerebral toxoplasmosis, PML and AIDS-related dementia (P< 0.0001). The sensitivity and specificity of sCD23 in CSF as a marker for detection of brain NHL were 77% and 94%, respectively. High levels of sCD23 were found in CSF from patients with brain NHL independently of the presence (18 out of 26) or absence (8 out of 26) of EBV DNA.ConclusionsThe sCD23 in CSF of HIV-1-infected patients may represent an additional, non-invasive marker for diagnosis of brain involvement in AIDS-related NHL.