Detection of cell-free human immunodeficiency virus in cerebrospinal fluid by using immune scanning electron microscopy.

The cerebrospinal fluid of 52 patients with human immunodeficiency virus type 1 (HIV-1) infection was incubated with polystyrene microspheres coated with monoclonal antibodies specific for HIV-1 core or envelope antigens. The beads were then collected on a filter surface and inspected by scanning electron microscopy (SEM). In 37 of 51 samples from subjects with chronic HIV-1 infection and from all three patients with primary HIV-1 infection, with or without neurologic symptoms, particles of 50-75 nm and 100-125 nm were visualized on beads coated with antibodies to HIV-1 core and envelope antigens, respectively. No such binding of particles was detected in the controls. Findings using immune SEM, which was found to be as sensitive as virus isolation, indicate that HIV-1 can replicate in the central nervous system (CNS) of patients with primary or chronic HIV-1 infection without causing neurologic symptoms. Production of cell-free virus seems to occur in the CNS of the majority of HIV-1-infected patients.