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Survival of intracellular pathogens within human mononuclear phagocytes
1Division of Infectious Diseases, Cornell University Medical College, New York, NY 10021.
Abstract:
The preceding discussion makes it clear that there are multiple determinants, related to the microorganism, the host defense cell, and the presence of activating T cell stimuli that must be considered when examining at the cellular level how and why intracellular pathogens are able to cause infection. From the standpoint of the interaction of the mononuclear phagocyte's antimicrobial mechanisms with T gondii, L donovani, and C psittaci, the determinants which appear to influence directly the outcome of intracellular infection include: a. the magnitude of the phagocyte's respiratory burst capacity; b. the ability to respond specifically and effectively to microbial ingestion with the generation of O2- and H2O2; c. susceptibility to H2O2; and d. the presence of and susceptibility to oxygen-independent mechanisms. T cell dependent enhancement of the mononuclear phagocyte's antimicrobial mechanisms is a particularly critical element in cellular resistance to infection, and thus, host defense. If the activated state is not properly achieved, the macrophage remains susceptible to and perpetuates intracellular infections.
Insights
Understanding intracellular pathogen infection requires examining host defense cells and microbial factors. Key determinants include the mononuclear phagocyte
Area of Science:
- Cellular microbiology
- Immunology
- Host-pathogen interactions
Background:
- Intracellular pathogens pose significant challenges to host defense mechanisms.
- Understanding the cellular basis of infection is crucial for developing effective treatments.
- Mononuclear phagocytes play a central role in combating intracellular microbial invaders.
Purpose of the Study:
- To elucidate the cellular determinants governing intracellular pathogen infection.
- To explore the interaction between mononuclear phagocytes and specific intracellular pathogens.
- To identify critical factors influencing the outcome of intracellular infections at the cellular level.
Main Methods:
- Analysis of mononuclear phagocyte antimicrobial mechanisms.
- Examination of interactions with intracellular pathogens like Toxoplasma gondii, Leishmania donovani, and Chlamydia psittaci.
- Assessment of host cell responses, including respiratory burst capacity and oxygen-independent mechanisms.
Main Results:
- Multiple determinants influence intracellular infection outcomes, involving the microorganism, host cell, and T cell stimuli.
- Key factors include phagocyte respiratory burst capacity, reactive oxygen species generation (O2-, H2O2), susceptibility to H2O2, and oxygen-independent mechanisms.
- T cell-dependent enhancement of macrophage antimicrobial activity is critical for host defense.
Conclusions:
- Effective host defense against intracellular pathogens relies on robust mononuclear phagocyte antimicrobial mechanisms.
- Proper activation of macrophages, particularly through T cell-dependent pathways, is essential to prevent pathogen persistence.
- Failure to achieve an activated macrophage state renders the host susceptible to and perpetuates intracellular infections.