MCB3020 Homework Set 4 Notes

Overview of the Human Microbiome and Immunity

  • Gut Microbial Community and Energy Recovery
    • Contribution to energy recovery via enzymatic abilities not found in human genome.
      • Example: Crude fiber digestion from plants requires bacteria; mammals lack necessary enzymes.
    • Methanogens can enhance nutrient availability for the host.
    • Dysbiosis in gut flora can lead to obesity.

Immune System Components

  • Innate Immunity vs. Adaptive Immunity

    • Innate Immunity:
      • First line of defense.
      • Activated without prior pathogen exposure, targets all foreign particles.
    • Adaptive Immunity:
      • Involves specific recognition by B cells and T cells.
      • Produces antibodies that bind to specific antigens.

  • Immediate Response vs. Long-term Defense

    • Innate Immunity:
      • Fastest response, comprises 80% of immune cells in lymphatic system.
    • Adaptive Immunity:
      • Provides long-term defense and memory against recurrent pathogens.
      • Involved in allergic reactions through hypersensitivity.

  • Influence of Early Life on Allergy Development

    • Lack of microflora transfer (e.g., C-section, lack of breastfeeding) can lead to immune hypersensitivity.

Inflammation Mechanisms

  • Inflammatory Response Triggers

    • Innate immunity activates inflammation through cytokine release from various cell types.
    • Activation of adaptive immunity involves antigen presentation to B and T cells.
    • Lymphocytes promote destruction of damaged cells.

  • Resolution of Inflammation

    • Controlled infections lead to removal of pathogens.
    • Reduction in inflammatory cells and cytokines, decreasing attraction for phagocytes.

Antibiotics and Their Effects

  • Antibiotic Use in Viral Infections

    • Prescription of antibiotics (e.g., Amoxicillin) for influenza is ineffective as antibiotics target bacterial infections, not viruses.

  • Immune Response to Antibiotics

    • Small molecules (<2000 Da) generally don't elicit immune responses.
    • Some antibiotics, such as penicillin, can cause allergic reactions.

  • Consequences of Incomplete Antibiotic Courses

    • Stopping antibiotics early can lead to antibiotic resistance by allowing pathogens to recover.
    • Over time, excessive antibiotic use can disrupt the microbiome, potentially causing obesity, inflammation, and colitis.
      • Evidence includes studies observing changes in gut bacteria and mucus production in treated mice.

Gnotobiotic Mice and Microbial Research

  • Gnotobiotic Mice:

    • Mice completely free of all microorganisms, often sickly and vulnerable to infections and diseases.
    • Useful for studying the roles of microbial strains and their interactions in the gut.

  • Examples of Human Microbial Symbionts

    • Bifidobacteria can break down plant polysaccharides that humans cannot digest themselves, indicating mutualistic relationships.

Sialic Acid in Immune Function

  • Definition:

    • Specialized 9-carbon amino sugars important for self-recognition in the immune system.

  • Role:

    • Sialic acids facilitate immune self-recognition and are exploited by pathogenic bacteria and viruses.
    • Their complex structures contribute to the spatial arrangement of epitopes, crucial for immune interactions.
    • Oligosaccharides aid in microbial recruitment for human development, providing a self-code for organisms.