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Impairment of phagosome-lysosome fusion in HIV-1-infected macrophages
H Moorjani1, B P Craddock, S A Morrison
1Division of Infectious Disease, University Medical Center, Stony Brook, New York, USA.
Abstract:
Phagosome-lysosome fusion is critical for intracellular killing of most organisms and is inhibited by some viruses, notably influenza. We explored the effects of infection in vitro with HIV-1 (IIIB or Ada-M) on phagosome-lysosome fusion in blood monocyte-derived macrophages. After 8 days of infection, fusion was assessed from the fluorescence change occurring up to 2 h after labeling the lysosome compartment with acridine orange and loading of phagosomes with opsonized yeast. Compared with mock-infected control macrophages, the proportion of cells showing fusion after infection was reduced from a mean of 70% to a mean of 47% (p = 0.0001). Inhibition was seen with heat-killed HIV-1 IIIB but not virus-free filtrate. It was mimicked by recombinant gp 120 and blocked by soluble CD4 or antibody to CD4 but not by a neutralizing antibody to the V3 loop of gp 120. The inhibitory effect was seen 8 days after the original, transient exposure to gp 120. These results suggest that a lasting abnormality of phagosome-lysosome fusion results from interaction between gp 120 and CD4, contributing, perhaps, to the increased susceptibility to opportunistic infections of people infected with HIV.
Insights
HIV-1 infection impairs phagosome-lysosome fusion in macrophages, a key process for killing pathogens. This dysfunction, caused by the gp120 protein interacting with CD4, may increase opportunistic infections in people with HIV.
Area of Science:
- Immunology
- Virology
- Cell Biology
Background:
- Phagosome-lysosome fusion is essential for macrophage antimicrobial activity.
- Viral infections, like influenza, can disrupt this crucial cellular process.
- Human Immunodeficiency Virus type 1 (HIV-1) infection is associated with increased susceptibility to opportunistic infections.
Purpose of the Study:
- To investigate the impact of HIV-1 infection on phagosome-lysosome fusion in human macrophages.
- To identify the viral component responsible for inhibiting phagosome-lysosome fusion.
- To elucidate the mechanism by which HIV-1 affects phagosome-lysosome fusion.
Main Methods:
- Monocyte-derived macrophages were infected in vitro with HIV-1 strains.
- Phagosome-lysosome fusion was assessed using acridine orange labeling and opsonized yeast phagocytosis.
- The role of HIV-1 components, including gp120 and CD4 interaction, was evaluated using recombinant proteins, soluble CD4, and antibodies.
Main Results:
- HIV-1 infection significantly reduced the proportion of macrophages exhibiting phagosome-lysosome fusion (from 70% to 47%).
- Heat-killed HIV-1 and recombinant gp120 inhibited fusion, while virus-free filtrate did not.
- The inhibitory effect was mediated by gp120 interaction with CD4 and persisted for at least 8 days post-exposure.
Conclusions:
- HIV-1 infection causes a persistent defect in phagosome-lysosome fusion in macrophages.
- The gp120-CD4 interaction is responsible for this functional impairment.
- This disruption of cellular defense mechanisms may contribute to the heightened risk of opportunistic infections in individuals with HIV.