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Updated: Jul 3, 2026
Live-cell Video Microscopy of Fungal Pathogen Phagocytosis
Published on: January 9, 2013
Analysis of PRA1 and its relationship to Candida albicans- macrophage interactions
1Genetics Group, Biotechnology Research Institute, National Research Council of Canada, Montreal, Québec, Canada. anne.marcil@cnrc-nrc.gc.ca
Abstract:
Phagocytosis of Candida albicans by either primary bone marrow-derived mouse macrophages or RAW 264.7 cells upregulated transcription of PRA1, which encodes a cell wall/membrane-associated antigen previously described as a fibrinogen binding protein. However, a pra1 null mutant was still able to bind fibrinogen, showing that Pra1p is not uniquely required for fibrinogen binding. As well, Pra1 tagged with green fluorescent protein did not colocalize with AlexaFluor 546-labeled human fibrinogen, and while PRA1 expression was inhibited when Candida was grown in fetal bovine serum-containing medium, Candida binding to fibrinogen was activated by these conditions. Therefore, it appears that Pra1p can play at most a minor role in fibrinogen binding to C. albicans. PRA1 gene expression is induced in vitro by alkaline pH, and therefore its activation in phagosomes suggested that phagosome maturation was suppressed by the presence of Candida cells. LysoTracker red-labeled organelles failed to fuse with phagosomes containing live Candida, while phagosomes containing dead Candida underwent a normal phagosome-to-phagolysosome maturation. Immunofluorescence staining with the early/recycling endosomal marker transferrin receptor (CD71) suggested that live Candida may escape macrophage destruction through the inhibition of phagolysosomal maturation.
Insights
Candida albicans phagocytosis by macrophages upregulates PRA1 gene expression. However, Pra1p plays a minor role in fibrinogen binding and live Candida inhibits phagolysosome maturation, potentially aiding immune evasion.
Area of Science:
- Microbiology
- Immunology
- Cell Biology
Background:
- Phagocytosis is a key immune mechanism for clearing microbial pathogens like Candida albicans.
- PRA1 encodes a cell wall antigen in C. albicans, previously implicated in fibrinogen binding.
- Understanding C. albicans interactions with host cells is crucial for developing antifungal strategies.
Purpose of the Study:
- To investigate the role of PRA1 in Candida albicans interaction with macrophages.
- To determine the function of Pra1p in fibrinogen binding to C. albicans.
- To elucidate the mechanism by which C. albicans evades macrophage-mediated destruction.
Main Methods:
- Macrophage phagocytosis assays using primary bone marrow-derived macrophages and RAW 264.7 cells.
- Analysis of PRA1 gene expression and protein localization.
- Fibrinogen binding assays with wild-type and mutant C. albicans strains.
- Phagosome maturation studies using fluorescently labeled organelles and markers.
Main Results:
- Phagocytosis of C. albicans upregulated PRA1 transcription in macrophages.
- A pra1 null mutant showed retained fibrinogen binding capacity, indicating Pra1p is not essential for this interaction.
- PRA1 expression was inversely correlated with fibrinogen binding conditions.
- Live C. albicans inhibited phagolysosome maturation, while dead cells underwent normal maturation, suggesting a mechanism for immune evasion.
Conclusions:
- Pra1p plays a minimal role in fibrinogen binding to C. albicans.
- Upregulation of PRA1 during phagocytosis may indicate suppressed phagosome maturation.
- Live C. albicans may escape macrophage destruction by inhibiting phagolysosomal maturation, potentially through mechanisms involving the transferrin receptor (CD71).
