Related Experiment Videos
Intracellular trafficking of Mycobacterium avium ss. paratuberculosis in macrophages
N F Cheville1, J Hostetter, B V Thomsen
1Department of Veterinary Pathology, Iowa State University, Ames, Iowa, USA. nchevill@iastate.edu
Abstract:
The granulomatous enteric lesions of cattle with Johne's disease are composed of infected macrophages, and grow by accumulation, re-infection, and expansion of macrophage populations in the intestinal wall. We have examined the growth of bacteria in macrophages to define characteristics of intracellular trafficking for exocytosis, replication, and antigen presentation. Using immunocytochemical markers for light, confocal and electron microscopy, we have examined potential pathway tropisms using data for bacterial attachment, phagosomal acidification, phagolysosomal degradation and apoptosis. Our hypotheses are that pathogenic/wild-type strains block phagosomal acidification so that the phagosome fails to obtain markers of the late phagosome and phagolysosome, and this leads to the replication pathway within bacteriophorous vacuoles. Non-pathogenic strains appear to be processed to exocytosis, and avirulent mutant strains may be degraded and have preference of antigen processing pathways that involve transport vesicles bearing MHC II antigens. Pathogenicity in a nude mouse model of intestinal infection reveals lesion development and confirms pathway preferences of virulent strains for bacteriophorous vacuole formation.
Insights
Pathogenic bacteria causing Johne's disease in cattle replicate within macrophages by blocking phagosomal acidification. Non-pathogenic strains are processed for exocytosis, while avirulent strains are degraded, aiding antigen presentation.
Area of Science:
- Microbiology
- Veterinary Pathology
- Cell Biology
Background:
- Johne's disease in cattle causes granulomatous enteric lesions due to infected macrophages.
- Bacterial growth within macrophages involves complex intracellular trafficking pathways.
Purpose of the Study:
- To define intracellular trafficking characteristics for bacterial exocytosis, replication, and antigen presentation.
- To investigate pathway tropisms of pathogenic and non-pathogenic bacterial strains within macrophages.
Main Methods:
- Utilized immunocytochemical markers for light, confocal, and electron microscopy.
- Examined bacterial attachment, phagosomal acidification, phagolysosomal degradation, and apoptosis.
- Employed a nude mouse model for intestinal infection studies.
Main Results:
- Pathogenic strains block phagosomal acidification, leading to replication in bacteriophorous vacuoles.
- Non-pathogenic strains undergo exocytosis.
- Avirulent strains are degraded and favor antigen processing via MHC II vesicles.
Conclusions:
- Bacterial strain virulence correlates with specific intracellular trafficking pathways within host macrophages.
- Understanding these pathways is crucial for developing strategies against Johne's disease.