Isolates of human immunodeficiency virus type 1 from the brain may constitute a special group of the AIDS virus.

The biologic, serologic, and molecular properties of isolates of human immunodeficiency virus type 1 (HIV-1) from the central nervous system (CNS) were determined and compared to those of isolates from peripheral blood and lymph nodes. Among these were pairs of CNS and blood isolates obtained from six infected individuals. The data show that HIV-1 isolates from the CNS can be distinguished from peripheral blood isolates by their (i) relative inability to infect established T-cell lines, (ii) reduced cytopathogenicity, (iii) inability to modulate CD4 antigen expression on infected cells, (iv) efficient replication in peripheral blood macrophages, and (v) insensitivity to serum neutralization. Paired CNS and peripheral blood isolates from the same individual also display some differences in cellular tropism. The blood isolates replicate better in T-cell lines and glioma cell lines, whereas the paired CNS isolates replicate more efficiently in primary macrophages. These results suggest that viruses isolated from the CNS of infected individuals may represent a specific HIV-1 subgroup.