Objectives: Characterization of the diarrhoea-inducing effect of altered cytokine production in HIV infection.
Methods: Monocyte-derived macrophages (MDM) were infected with macrophagetropic (SF162) and lymphocytotropic (IIIB) HIV-1 strains and cocultured with autologous peripheral blood mononuclear cells (PBMC). After 24 h the supernatants were collected and tested for their immunoreactive levels of cytokines by enzyme-linked immunosorbent assay. The effects of the supernatants and the respective recombinant human cytokines on barrier function of HT-29/B6 cells were determined.
Results: Infection of MDM with HIV-1 SF162 or IIIB led to increased production of tumour necrosis factor-alpha (TNFalpha), interleukin-1-beta, interferon-alpha and interferon-gamma after cell-cell contact with PBMC. Supernatants of infected cells decreased transepithelial resistance (R(t)), with higher effects on R(t) in HIV IIIB infection, which was due to higher cytokine concentrations. The effect was not due to cytotoxicity (negative LDH assay) or epithelial monolayer disruption [zonula occludens protein-1 (ZO-1) immunofluorescence staining]. The effect of HIV-1 IIIB coculture supernatants could be mimicked by the respective recombinant human cytokines. TNFalpha is an effector cytokine, because inhibition of TNFalpha by its soluble receptor decreased the effect of the supernatants on transepithelial resistance. Conductance scanning indicated the cytokine-induced barrier defect to be due to both, induction of epithelial apoptoses and tight junction alterations.
Conclusions: Cell-cell interaction of HIV-infected macrophages with PBMC leads to a release of cytokines sufficient to alter intestinal epithelial barrier function. The main effect was mediated by TNFalpha inducing a leak-flux which may contribute to the diarrhoea by HIV per se (HIV-enteropathy).