Immune Disorders, Vaccines, and Antimicrobial Therapy — Autoimmunity, Drug Resistance, and Immunotherapy Explained | Chapter 28 from Brock Biology of Microorganisms

How do immune disorders arise, how do vaccines and immunotherapies work, and what strategies are available to fight antimicrobial resistance? Chapter 28 of Brock Biology of Microorganisms explores immune hypersensitivities, autoimmunity, immunodeficiencies, vaccine development, modern immunotherapy, and the urgent global challenge of antimicrobial drug resistance. This summary synthesizes key mechanisms and strategies at the intersection of immunology, medicine, and public health.

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Immune Disorders and Deficiencies

Immune system dysfunction takes several forms:

• Hypersensitivities:
  • Type I (Immediate): IgE-mediated allergies (e.g., hay fever, anaphylaxis).
  • Type IV (Delayed): T cell-mediated responses (e.g., contact dermatitis, TB skin test).
• Autoimmunity: The immune system attacks self-antigens, leading to diseases like type 1 diabetes, Hashimoto’s thyroiditis, and lupus. Factors include autoantibodies, Th1 cells, genetics, the microbiome, and hygiene hypothesis.
• Superantigens: Bacterial proteins that overstimulate T cells, causing toxic shock and systemic inflammation.
• Immunodeficiencies:
  • Primary (e.g., SCID): Genetic B/T cell defects, treated with bone marrow transplant or gene therapy.
  • Secondary (e.g., AIDS): HIV destroys helper T cells, causing vulnerability to opportunistic infections.

Vaccination Strategies

Vaccines expose the immune system to antigens, priming adaptive immunity and building lasting protection. Types of vaccines include:

• Inactivated: Killed pathogens (e.g., Salk polio).
• Attenuated live: Weakened microbes (e.g., MMR).
• Toxoid: Inactivated toxins (e.g., tetanus, diphtheria).
• Subunit/acellular: Selected components (e.g., pertussis).
• Conjugate: Linked polysaccharides (e.g., Hib, pneumococcal).
• Recombinant protein/vector: Engineered antigens (e.g., hepatitis B, rabies).
• Nucleic acid: DNA or mRNA-based (e.g., COVID-19 vaccines).
• Plant-based: Antigens produced in transgenic plants.

Boosters extend protection, and vaccines have dramatically reduced the burden of many infectious diseases.

Immunotherapy Approaches

Immunotherapies are used to enhance or suppress immune responses, especially in cancer treatment:

• Cancer immunotherapy:
  • Prophylactic vaccines: HPV and hepatitis B vaccines prevent cancer.
  • Checkpoint inhibitors: Anti-PD-1 and anti-CTLA-4 antibodies restore T cell activity against tumors.
  • CAR T cells: Genetically engineered T cells that target specific tumor antigens.
• Gut microbiome: Can influence immunotherapy outcomes; fecal transplants may improve response in some patients.

Antimicrobial Drug Classes

Antimicrobial agents target vital pathogen processes:

• Cell wall synthesis: β-lactams (penicillin, cephalosporins), vancomycin, bacitracin.
• Protein synthesis (70S ribosomes):
  • 30S inhibitors: aminoglycosides, tetracyclines.
  • 50S inhibitors: macrolides (erythromycin), chloramphenicol.
• Nucleic acid synthesis: Quinolones (DNA gyrase), rifamycins (RNA polymerase).
• Metabolite analogs: Sulfa drugs, trimethoprim, isoniazid (TB).
• Membrane disruptors: Daptomycin (Gram-positives), polymyxins.
• Lipid biosynthesis inhibitors: Platensimycin, effective against resistant bacteria.

Antiviral and Antifungal Drugs

• Antivirals:
  • NRTIs/NNRTIs (e.g., AZT, nevirapine) target HIV reverse transcriptase.
  • Protease/fusion inhibitors (e.g., indinavir, enfuvirtide) block HIV maturation or entry.
  • Neuraminidase inhibitors (e.g., oseltamivir) treat influenza.
  • Interferons boost host antiviral defenses.
• Antifungals:
  • Ergosterol inhibitors (e.g., amphotericin B, azoles) disrupt fungal membranes.
  • Cell wall inhibitors (echinocandins, polyoxins).
  • Other classes: griseofulvin, 5-fluorocytosine.

Antimicrobial Resistance (AMR): Mechanisms and Solutions

Antimicrobial resistance arises by:

• Enzyme inactivation (e.g., β-lactamases)
• Altered drug targets
• Efflux pumps
• Alternative metabolic pathways

Resistance is fueled by antibiotic overuse, misuse, and horizontal gene transfer (such as R plasmids). Strategies to combat AMR include:

• Judicious antibiotic use
• Development of novel drugs and combinations (e.g., β-lactamase inhibitors)
• Targeting new microbial processes and using advanced drug delivery systems
• Computer-aided drug design
• Drug cocktails (e.g., HAART for HIV)

Glossary: Key Terms from Chapter 28

• Hypersensitivity: Harmful immune overreaction to harmless substances.
• Autoimmunity: Immune attack on self-antigens.
• Toxoid: Inactivated toxin used in vaccines.
• NRTI / NNRTI / Protease inhibitor: Antiviral drug classes.
• Superantigen: Protein that massively stimulates T cells.
• CAR T cells: Genetically engineered T cells for targeted therapy.
• Selective toxicity: Drugs that target pathogens without harming the host.
• AMR: Antimicrobial resistance via mutation or gene transfer.

Conclusion: Facing the Challenges of Immune Disorders and Resistance

Chapter 28 emphasizes the growing importance of understanding immune dysfunction, innovating vaccination and immunotherapy strategies, and addressing the threat of antimicrobial resistance. Modern medicine relies on continued scientific advancement and responsible stewardship of antimicrobial agents.

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