Factors affecting invasion of HT-29 and HEp-2 epithelial cells by organisms of the Mycobacterium avium complex
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1Kuzell Institute for Arthritis and Infectious Diseases, California Pacific Medical Center Research Institute, San Francisco 94115.
Abstract:
Organisms of the Mycobacterium avium complex cause disseminated blood-borne infection in patients with AIDS, who acquire the infection mainly through the gastrointestinal tract. Prior to causing infection, M. avium must colonize and invade the intestinal mucosa. This study examined the ability of several serovars of the M. avium complex to bind to and invade the HT-29 intestinal mucosal cell line and the HEp-2 laryngeal cell line. Logarithmic-phase M. avium was more efficient in binding and invasion than organisms in the stationary phase of growth. Bacteria incubated at 37 and 40 degrees C adhered to and invaded HT-29 cells more efficiently than bacteria cultured at 30 degrees C. The ability of M. avium to invade HT-29 and HEp-2 cells was inhibited when the cells were incubated with cytochalasin B prior to exposure to the bacterium, suggesting active participation of the mammalian cell in the process of internalization. Two protein kinase inhibitors, staurosporine and H7, blocked invasion of M. avium, and a specific tyrosine protein kinase inhibitor, genistein, also blocked the internalization but not the binding of bacteria. The findings suggest that M. avium binds to a specific receptor(s) on the epithelial cells and uses the cytoskeleton of the mammalian cell to become internalized.
Insights
Mycobacterium avium complex invades intestinal cells using host cell machinery. This study reveals bacterial growth phase and temperature affect invasion, highlighting host cell participation in M. avium infection.
Area of Science:
- Microbiology
- Cell Biology
- Infectious Diseases
Background:
- Mycobacterium avium complex (MAC) causes disseminated infections in AIDS patients, primarily through gastrointestinal tract acquisition.
- Successful MAC infection requires colonization and invasion of the intestinal mucosa.
- Understanding MAC's interaction with intestinal cells is crucial for developing therapeutic strategies.
Purpose of the Study:
- To investigate the binding and invasion capabilities of MAC serovars.
- To examine the influence of bacterial growth phase and temperature on MAC adherence and invasion.
- To elucidate the host cell mechanisms involved in MAC internalization.
Main Methods:
- Utilized HT-29 intestinal mucosal and HEp-2 laryngeal cell lines.
- Compared binding and invasion efficiency of logarithmic-phase versus stationary-phase M. avium.
- Assessed the effect of incubation temperatures (30, 37, 40 degrees C) on bacterial interaction with cells.
- Investigated the role of host cell cytoskeleton and protein kinases (cytochalasin B, staurosporine, H7, genistein) in MAC internalization.
Main Results:
- Logarithmic-phase M. avium demonstrated higher binding and invasion efficiency than stationary-phase organisms.
- Incubation at 37 and 40 degrees C enhanced M. avium adherence and invasion of HT-29 cells compared to 30 degrees C.
- Cytochalasin B inhibited M. avium invasion, indicating active host cell involvement.
- Protein kinase inhibitors (staurosporine, H7, genistein) blocked M. avium internalization, with genistein specifically affecting internalization but not binding.
Conclusions:
- M. avium likely binds to specific receptors on epithelial cells.
- Bacterial internalization involves the host cell's cytoskeleton.
- Host cell protein kinases play a role in M. avium invasion, suggesting active participation of the host cell in the infection process.