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Proteinase K-sensitive and filterable phagosome-lysosome fusion inhibiting factor in Afipia felis
Abstract:
Afipia felis is one of the putative agents of cat scratch disease (CSD). Its intracellular location was previously demonstrated in tissue sections. It has been recently grown in human monocytes and in HeLa cells. We report that A. felis may infect human macrophages and the P 388 D1 murine macrophage cell line, yet is unable to grow in the cell-free culture medium. In both human macrophages and P 388 D1, the organisms multiply in a vacuole after active inhibition of phagosome-lysosome fusion (P-L) as demonstrated with cationized ferritin-labeled lysosomes. This P-L fusion inhibition is diffusable and is due to a filterable factor which is inactivated by protease digestion. The pathogenic role of A. felis in CSD may result from its ability to invade and multiply in macrophages.
Insights
Afipia felis, a cause of cat scratch disease (CSD), infects human macrophages by preventing phagosome-lysosome fusion. This allows the bacteria to multiply within macrophages, contributing to CSD pathogenesis.
Area of Science:
- Bacteriology
- Immunology
- Cell Biology
Background:
- Afipia felis is a suspected cause of cat scratch disease (CSD).
- Previous studies confirmed its intracellular presence in tissue sections and growth in monocytes and HeLa cells.
- The bacterium's intracellular lifestyle and mechanisms of immune evasion are not fully understood.
Purpose of the Study:
- To investigate the interaction of Afipia felis with human macrophages.
- To elucidate the mechanism by which A. felis survives and replicates within host cells.
- To determine the role of phagosome-lysosome fusion in A. felis infection.
Main Methods:
- Infection of human macrophages and the P 388 D1 murine macrophage cell line with A. felis.
- Microscopic observation of bacterial intracellular localization and replication.
- Assays to assess phagosome-lysosome (P-L) fusion using cationized ferritin-labeled lysosomes.
- Analysis of the nature of the factor inhibiting P-L fusion (diffusible, filterable, protease-sensitive).
Main Results:
- Afipia felis successfully infects human macrophages and the P 388 D1 cell line.
- A. felis replicates within a vacuole inside these cells, but not in cell-free culture.
- Infection is associated with active inhibition of phagosome-lysosome fusion.
- The inhibitory factor is diffusable, filterable, and inactivated by protease treatment.
Conclusions:
- Afipia felis invades and replicates within macrophages.
- The bacterium actively inhibits phagosome-lysosome fusion, a key mechanism for its intracellular survival.
- This ability to evade lysosomal degradation likely contributes to the pathogenesis of cat scratch disease.