pathogen variations

Overview of Journal Club and Final Lecture

  • Final journal session taking place on Friday.

  • Last lecture scheduled for the following Monday, focused on journal club topics.

  • Students are encouraged to complete their journal club worksheets.

  • A challenge is presented to students regarding experimental weaknesses:
      - Identify one experimental weakness in studies but avoid suggesting use of human or nonhuman primates for the resolution.
      - Acknowledge potential difficulties in recruiting human participants for ongoing studies.

Mechanisms of Antigen Modulation by Pathogens

  • Discussion on how pathogens evade the immune system through various antigen modulation techniques.

  • Pathogen strategies encompass both innate and adaptive immunity.

  • Key focus on antigen modulation mechanisms affecting immune recognition.

Major Mechanisms of Antigen Modulation

  • Antigen modulation aids pathogens in avoiding detection by:
      - Antibodies
      - T cells
      - Phagocytes

  • Three primary mechanisms identified:
      1. Epitope Masking
      2. Antigen Variation
      3. Phase Variation

1. Epitope Masking

  • Definition: The alteration of the 3D structure of an antigen to hide epitopes from the immune response.

  • Epitope: The specific site on an antigen where antibodies bind.

  • Pathogen behavior:
      - Changing the 3D structure of the antigen also alters the epitope—compares to modeling with Play-Doh, where altering one part affects the overall shape.
      - Example of cryptic epitopes:
        - .

2. Antigen Variation

  • Definition: Alternating the surface antigens a pathogen expresses to confuse the immune system.

  • Comparison to gene conversion:
      - Although not necessary for the exam, understanding antigen variation is critical for grasping immune evasion.

  • Mechanism:
      - Pathogen possesses multiple antigenic forms (such as A or B versions) and can switch between these forms during infection.
      - Control of transcription in bacteria allows them to select which protein version to express at any time, complicating the immune response.

3. Phase Variation

  • Definition: A binary switch of surface molecule expression either on or off.

  • Mechanism of action:
      - Environmental triggers (e.g., temperature or pH) activate or inactivate certain expressions in the pathogen.
      - Example: Bacteria like Neisseria can control the expression of outer membrane proteins critical for attachment and immune evasion.

Immune Response Strategies and Phagocytosis

  • After pathogen entry, the immune system initiates several processes:
      - Phagocytosis: A critical mechanism where immune cells engulf pathogens.
      - Problems posed by pathogens to evade this response include:
        - Killing phagocytes
        - Preventing phagocytosis uptake
        - Resisting killing once inside a phagocyte.

Mechanisms of Phagocytosis Evasion

  • Phagocyte Death: Killing of the phagocyte stops immunological response.

  • Uptake Resistance: Pathogens can evade detection or ingestion by phagocytes.

  • Killing Resistance: Even after uptake, some pathogens resist intracellular killing by phagocytes.

Antigen Presentation and Immune Evasion

  • Antigen presentation is how the immune system displays pathogen-derived antigens to T cells.

  • Pathogen strategies can disrupt this process:
      - Various molecular mechanisms specific to pathogen types exist, focusing on affecting MHC Class II presentation.

  • Importance of understanding how these strategies allow pathogens to evade recognition by T cells:
      - Include suppression of immune cell activation and manipulation of inflammatory responses (e.g., IL-10).

Connection to Journal Club Assignments

  • Students should understand and apply these concepts to their journal reflections and discussions during the journal club.

  • Recognition of specific pathogens and their mechanisms is crucial for effectively engaging with assignment prompts and exam questions.
      - Anticipate how knowledge of immune evasion mechanisms links to the overall immune strategy against pathogens.

Final Notes

  • The provided pathways for understanding immune evasion strategies are complex and interconnected.

  • Students should explore different facets of the immune response and how pathogens exploit these for survival to prepare adequately for examinations.

  • Encourage questions and discussions on individual mechanisms as they appear interrelated and relevant across various topics in immunology and pathogen interactions.