Relationship between the occurrence of virus in plasma and cerebrospinal fluid of HIV-1 infected individuals

Attempts to isolate human immunodeficiency virus type 1 (HIV-1) were carried out on cerebrospinal fluid (CSF) and blood plasma samples from 111 HIV-1 infected subjects in various stages of infection. HIV-1 was recovered at a low rate from CSF of persons with normal immunological parameters but frequently from patients with abnormal values, in all stages of immune system involvement. Isolation from plasma was positive in the majority of the patients, in all stages of infection, with a frequency that was related to the degree of immunodeficiency. HIV-1 could be recovered from the CSF of most patients (74%) with viremia when 85 paired specimens of 58 patients were analyzed. By contrast, HIV-1 was isolated from CSF, but not from plasma, in one case only. HIV-1 p24 antigen measured by an enzyme-linked immunosorbent assay (ELISA) was detectable in only four CSF samples compared with 15 serum samples in paired specimens. These findings indicate that most patients with HIV-1 infection have circulating cell-free infectious virus in the blood and simultaneously demonstrable HIV-1 in the CSF. Replication of HIV-1 exclusively in the central nervous system (CNS) appears to be a rare event.