To characterize the host range of different strains of HIV-1, we have used four types of cells, primary monocyte-derived macrophages (MDM), primary PBL, a promonocyte cell line (U937), and a CD4+ T cell line (SUP-T1). These cells were infected with three prototype strains of HIV-1, a putative lymphocyte-tropic strain (IIIB), and two putative monocyte-tropic strains (SF162 and DV). Infections were monitored by assays for infectious virus, for cell-free and cell-associated viral antigen (p24), and for the proportion of cells infected by immunohistochemical staining. It was concluded that: (a) the use of four different cell types provides a useful biological matrix for distinguishing the tropism of different strains of HIV-1; this matrix yields more information than the infection of any single cell type. (b) A monocyte-tropic strain of HIV-1, such as strain SF162, shows a reciprocal host range when compared with a lymphocyte-tropic strain such as IIIB; strain SF162 replicates well in primary MDM but not in U937 or SUP-T1 cells, while strain IIIB replicates well in both U937 and SUP-T1 cells but not in MDM. (c) Both lymphocyte-tropic and monocyte-tropic strains of HIV-1 replicate well in PBL. (d) The promonocyte cell line, U937, and the T cell line, SUP-T1, differ markedly from primary cells, such as MDM and PBL, in their ability to support the replication of different strains of HIV-1; these cell lines cannot be used as surrogates for primary cells in host range studies of HIV-1 strains.

To characterize the role of CD4 in human immunodeficiency virus type 1 (HIV-1) infection of macrophages, we examined the expression of CD4 by primary human monocyte-derived macrophages and studied the effect of recombinant soluble CD4 and anti-CD4 monoclonal antibodies on HIV-1 infection of these cells. Immunofluorescence and Western blot (immunoblot) studies demonstrated that both monocytes and macrophages display low levels of surface CD4, which is identical in mobility to CD4 in lymphocytes. Recombinant soluble CD4 and the anti-CD4 monoclonal antibody Leu3a blocked infection of macrophages by three different macrophage-tropic HIV isolates, and the cytopathic effects of HIV-1 infection were similarly prevented. Dose-response experiments using a prototype isolate which replicates in both macrophages and T lymphocytes showed that recombinant soluble CD4 inhibited infection of macrophages more efficiently than in lymphocytes. These results indicate that CD4 is the dominant entry pathway for HIV-1 infection of macrophages. In addition, recombinant soluble CD4 effectively blocks HIV-1 infection by a variety of macrophage-tropic strains and thus has the potential for therapeutic use in macrophage-dependent pathogenesis in HIV disease.

We have investigated the susceptibility of cord blood monocyte-derived macrophages to human immunodeficiency virus type 1 (HIV-1) infection in vitro. Cord blood monocytes were maintained in vitro for 10 to 15 days and then infected with HIV-1. Syncytia were observed 14 days after infection by light microscopy. Viral proteins were detected by immunofluorescence assay. Electron microscopic examination demonstrated typical lentivirus particles within cytoplasmic vacuoles. The supernatants from the HIV-1-infected cultures also contained significant reverse transcriptase activity and p24 antigen. Like adult monocyte/macrophages, cord-derived monocyte/macrophages expressed the CD4 receptor molecule. Pretreatment with blocking antibody prior to infection with HIV-1 Bal significantly reduced or blocked infection of cord monocyte/ macrophages. When cord and adult monocyte/macrophages were infected with HIV-1 Bal or Ada-M and directly compared, higher reverse transcriptase activities and p24 antigen expression were obtained with cord monocyte/macrophages. However, no significant difference was found between adult and cord monocyte/ macrophages infected with HIV-1 IIIB. These observations suggest that cord monocyte-derived macrophages may be important in the pathogenesis of pediatric AIDS and that the increased susceptibility of cord monocyte/macrophages to HIV-1 infection in vitro may be relevant to the enhanced susceptibility of neonates to HIV-1 diseases in vivo.

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