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Published on: April 2, 2013
The intracellular pathogen concept
Arturo Casadevall1, Ferric C Fang2
1Department of Molecular Microbiology and Immunology, Johns Hopkins School of Public Health, Baltimore, MD, USA.
Abstract:
The intracellular pathogen concept classifies pathogenic microbes on the basis of their site of replication and dependence on host cells. This concept played a fundamental role in establishing the field of cellular microbiology, founded in part by Dr. Pascale Cossart, whose seminal contributions are honored in this issue of Molecular Microbiology. The recognition that microbes can access and replicate in privileged compartments within host cells has led to many new and fruitful lines of investigation into the biology of the cell and mechanisms of cell-mediated immunity. However, like any scientific concept, the intracellular pathogen concept can become a dogma that constrains thinking and oversimplifies complex and dynamic host-pathogen interactions. Growing evidence has blurred the distinction between "intracellular" and "extracellular" pathogens and demonstrated that many pathogens can exist both within and outside of cells. Although the intracellular pathogen concept remains useful, it should not be viewed as a rigid classification of pathogenic microbes, which exhibit remarkable variation and complexity in their behavior in the host.
Insights
The intracellular pathogen concept, crucial for cellular microbiology, is being re-evaluated. Pathogen behavior blurs the lines between intracellular and extracellular, highlighting complex host-pathogen interactions.
Area of Science:
- Microbiology
- Cell Biology
- Immunology
Background:
- The intracellular pathogen concept defines microbes by their replication site and host cell dependence.
- This concept was foundational to cellular microbiology and understanding host-pathogen interactions.
- It spurred research into host cell biology and cell-mediated immunity.
Purpose of the Study:
- To critically evaluate the utility and limitations of the intracellular pathogen concept.
- To discuss the evolving understanding of host-pathogen dynamics.
- To acknowledge the contributions of Dr. Pascale Cossart to cellular microbiology.
Main Methods:
- Conceptual analysis of the intracellular pathogen concept.
- Review of emerging evidence on pathogen behavior.
- Discussion of host-pathogen interactions in cellular microbiology.
Main Results:
- The strict classification of pathogens as solely intracellular or extracellular is increasingly challenged.
- Many pathogens exhibit dynamic behavior, existing both inside and outside host cells.
- Evidence suggests a spectrum of pathogen-host interactions rather than rigid categories.
Conclusions:
- The intracellular pathogen concept remains a useful framework but should not be rigidly applied.
- Host-pathogen interactions are complex and dynamic, defying simple classification.
- Recognizing this complexity advances our understanding of microbial pathogenesis and immunity.
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