Pathogen Immune System and Pathogen Interaction Study Notes

Overview of the Immune System

  • Microorganisms and Immune System

    • Focus on how microorganisms invade the mixed immune system.

  • Innate Immune System

    • Definition: The innate immune system is the part of our immune system that responds immediately to pathogens without the need for prior exposure.

    • Function: Serves as the first line of defense against infections.

    • Overview:

    • Discuss basic functions of the innate immune system without going into extensive detail.

    • Recognize tissue injury as a potential breach in natural protective barriers, allowing pathogens to enter.

Inflammation

  • Function of Inflammation

    • Inflammation is the body's response to injury or infection, facilitating the movement of immune cells to the site of infection.

  • Characteristics of Inflammation

    • Five main characteristics: heat, redness, swelling, pain, and loss of function.

    • Cause of characteristics: Increased blood flow to the site of injury, attracting white blood cells and fluids.

  • Local vs. Chronic Inflammation

    • Localized: Typically short-lived at the site of infection.

    • Chronic: Can occur due to prolonged inflammation, potentially harming the body.

Mechanisms of Pathogen Interaction with Inflammation

  • Pathogens and Inflammation

    • Some pathogens may promote inflammation as a survival mechanism, leading to questions about their strategies.

    • Theoretical Discussion:

    • A theory proposed was that pathogens may attract immune cells to one area to facilitate infection elsewhere, similar to the military strategy of Blitzkrieg.

    • Additionally could be unintended consequences where pathogens indirectly affect inflammatory responses.

  • Hypothetical Pathogen Behavior

    • Pathogens may activate inflammation deliberately or influence related immune processes to dampen or augment inflammation.

Phagocytosis

  • Definition of Phagocytosis

    • Phagocytosis is the process by which certain white blood cells ingest and destroy pathogens.

    • Specific white blood cells involved:

    • Phagocytes: Specialized white blood cells capable of phagocytosis.

    • Major types of phagocytes:

      • Neutrophils

      • Macrophages

      • Dendritic Cells

Phagocyte Functions and Roles

  • Location of Phagocytes

    • Macrophages and dendritic cells: Reside in tissues, act as sentinels.

    • Neutrophils: Circulate in the blood and must be recruited to infection sites.

  • Pattern Recognition Receptors (PRRs)

    • Role: Recognize common patterns on pathogens, such as peptidoglycan or specific proteins on fungi/viruses.

    • PRRs do not recognize specific pathogen parts but common patterns shared among many pathogens.

Steps of Phagocytosis

  1. Recognition and Attachment

    • PRRs on phagocytes recognize and attach to pathogens.

  2. Engulfment

    • Phagocyte envelops the pathogen, moving it into the cell.

  3. Formation of Phagosome

    • The engulfed pathogen is contained within a phagosome, preventing it from interacting with other cellular structures.

  4. Phagolysosome Formation

    • The phagosome fuses with a lysosome, forming a phagolysosome containing digestive enzymes.

  5. Pathogen Killing

    • Enzymes and chemicals from the lysosome destroy the pathogen within the phagolysosome.

  6. Debris Cleanup

    • Macrophages clean up debris from the site of infection post-killing.

Pathogen Antiphagocytic Strategies

  • Potential Evading Phagocytosis

    • Identify points within the phagocytosis process where pathogens may interfere.

    • Strategies:

    1. Kill the phagocyte directly.

    2. Resist uptake by the phagocyte.

    3. Resist killing within the phagolysosome.

  • Killing Phagocytes

    • Some pathogens can directly destroy the phagocyte, stopping phagocytosis immediately.


    • Strategies include:

    • Reducing recruitment of phagocytes to the infection site.

    • Evading signals that attract phagocytes (e.g., proteases degrade chemokines).

    • Bypassing or blocking PRR recognition.

Examples of Pathogen Strategies

  • Candida albicans

    • Can grow hyphae within phagocytes leading to the bursting of the phagocyte.

  • Plasmodium (malaria)

    • Induces apoptosis in macrophages, avoiding destruction.

Resisting Killing in Phagolysosome

  • Pathogen Use of Phagocytes

    • Certain pathogens exploit phagocytes as protective environments to replicate undetected.

  • Strategies to Avoid Killing

    • Prevent maturation of phagosomes, manage pH levels within the phagosome, and prevent fusion with lysosomes.

    • Escape from phagosomes into the cytoplasm to evade detection and destruction.

Conclusion

  • Implications for Vaccines and Treatments

    • Understanding these interactions and evasion methods informs the development of vaccines and therapeutic strategies to counter infections effectively.

  • Further Discussion

    • Clarification of pathogen mechanisms as crucial in advancing immunological knowledge and potential clinical applications.