ObjectiveTo directly infect human fetal intestine with HIVin vitro.DesignHuman fetal intestinal explant cultures were exposed to HIV-1 and monitored for evidence of infection by biochemical assay, immunohistochemistry andin situhybridization.MethodsHuman fetal intestinal explants (14–21 weeks) were established in culture and exposed to HIV-1. Tissue culture fluid was assayed for p24 antigen and reverse transcriptase activity over a 14-day period. Explants were removed from culture on days 4, 7, 10 and 14 postinoculation and subjected (1) to immunohistochemistry to detect p24 and gp160/41 antigens, and (2) toin situhybridization to detect HIV-1 RNA. Explant tissue culture fluid was cocultured with Jurkat T-cells to detect infectious viral particles.ResultsReverse transcriptase activity and p24 antigen levels in fetal explant culture fluid rose between 7 and 14 days after viral inoculation. Jurkat T-cell cocultures confirmed the presence of infectious virus. Cells in the lamina propria resembling lymphocytes and macrophages of both small intestine and colon stained positively for the viral proteins p24 and gp41. The same type of cells also stained positively for HIV-1 RNA usingin situhybridization. Dual-label immunohistochemistry, combined immunohistochemistry andin situhybridization confirmed the presence of viral protein and RNA in cells bearing the CD3, CD4 (lymphocyte) or CD68 (macrophage) surface markers. There was no evidence at any time of HIV-1 infection of epithelial cells.ConclusionsCells of the lamina propria of the small intestine and colon, bearing lymphocyte or macrophage markers, can be directly infected by and support the replication of HIV-1. Such infection may be implicated in the pathogenesis of HIV enteropathy.