Replicative characteristics of primary isolates of the human immunodeficiency virus type 1 in peripheral blood mononuclear cells, primary macrophages and CD4+ transformed T-cell lines

Macrophage-tropic strains of HIV-1 are selectively transmitted and play a significant role in HIV-1 persistence, dissemination and disease progression. Most primary HIV-1 isolates productively infect primary macrophages but fail to infect or induce syncytium (non-syncytium-inducing or NSI) in CD4+ transformed T-ceil lines. Therefore, NSI isolates are considered to be macrophage-tropic. In order to select truly macrophage-tropic primary HIV-1 isolates for pathogenesis studies the replicative characteristics of a panel of eight primary (predominantly NSI) HIV-1 isolates were examined in primary macrophage cultures. This was not previously done. Stocks of these isolates were prepared in peripheral blood mononuclear cells (PBMC) and their replication in peripheral blood-derived macrophages and in CD4+ transformed T-cell lines examined based on the p24 antigen level in the cultures. Seven of the eight isolates did not replicate or induce syncytia (non-syncytium-inducing or NSI) in MT-2 cells, but one isolate replicated efficiently and induced large syncytia (syncytium-inducing or SI) in both the MT-2 and another transformed T-cell line (CEMx174). When replication of the isolates in peripheral blood-derived macrophages was examined, six of the seven NSI isolates replicated indicating that not all NSI isolates were capable of replicating in primary macrophages. Further, one of the six NSI isolates replicated (but did not induce syncytia) in the CEMx174 cell line, illustrating that characterization of primary isolates based on replication in one cell system does not allow predictions for other cell systems.