1. Overview

Immunology is the branch of biology that studies the immune system, its structure and function, disorders, and its role in health and disease. The immune system protects organisms from infection through layered defenses of increasing specificity.

2. Components of the Immune System

2.1 Innate Immunity

  • First line of defense
  • Non-specific, immediate response
  • Includes:
    • Physical barriers (skin, mucous membranes)
    • Chemical barriers (stomach acid, enzymes)
    • Cellular defenses (phagocytes, natural killer cells)

2.2 Adaptive Immunity

  • Second line of defense
  • Highly specific, slower to activate
  • Features memory (faster, stronger response upon re-exposure)
  • Main components:
    • B lymphocytes (B cells): Produce antibodies
    • T lymphocytes (T cells): Helper, cytotoxic, regulatory functions

3. Immune System Organs

  • Primary organs: Bone marrow, thymus
  • Secondary organs: Spleen, lymph nodes, tonsils, Peyer’s patches

4. Immune Response Phases

  1. Recognition: Detection of pathogens via pattern recognition receptors (PRRs)
  2. Activation: Signaling cascades, cytokine release, and immune cell recruitment
  3. Effector: Elimination of pathogens (phagocytosis, cytolysis)
  4. Resolution: Downregulation of response, memory cell formation

5. Humoral vs. Cellular Immunity

Humoral Immunity Cellular Immunity
Mediated by antibodies Mediated by T cells
Targets extracellular pathogens Targets intracellular pathogens

6. Diagram: Immune System Overview

Immune System Diagram

7. Recent Breakthroughs (2020+)

  • Single-cell RNA sequencing has enabled mapping of immune cell diversity at unprecedented resolution, revealing new immune cell subtypes and states.
  • CRISPR-based therapies are being tested to engineer immune cells (e.g., CAR-T cells) for targeted cancer treatment.
  • SARS-CoV-2 research: Studies show that some individuals have pre-existing T cell immunity to COVID-19, possibly due to exposure to common cold coronaviruses.
    • Reference: Grifoni et al., Cell, 2020 (link)
  • Neoantigen vaccines: Personalized cancer vaccines are being developed to train the immune system to recognize unique tumor antigens.

8. Surprising Facts

  1. The gut contains 70% of the body’s immune cells, making the digestive tract a major immune organ.
  2. Some immune cells can “remember” pathogens for decades—longer than previously thought.
  3. Plants and invertebrates have immune memory-like responses despite lacking adaptive immunity.

9. Memory Trick

“B comes before T, and B cells make Bodies (antibodies); T cells Target infected cells.”

10. Environmental Implications

  • Pollution and climate change can impair immune function, increasing susceptibility to infections and allergies.
  • Microplastic exposure is linked to altered immune responses in marine and terrestrial animals.
  • Biodiversity loss may reduce exposure to beneficial microbes, potentially increasing autoimmune and allergic diseases (the “Old Friends” hypothesis).
  • Emerging pathogens: Environmental disruption can lead to zoonotic spillover, challenging immune systems with novel threats.

11. Disorders of the Immune System

  • Autoimmune diseases: Immune system attacks self-tissues (e.g., Type 1 diabetes, lupus)
  • Immunodeficiency: Inadequate immune response (e.g., HIV/AIDS, primary immunodeficiencies)
  • Hypersensitivity: Overreaction to harmless antigens (e.g., allergies, asthma)

12. Vaccines: How They Work

  • Mimic infection to train immune memory without causing disease
  • Types:
    • Live-attenuated
    • Inactivated
    • Subunit, recombinant
    • mRNA (e.g., COVID-19 vaccines)

13. Diagram: Antibody Structure

Antibody Structure

14. Citation

15. Key Terms

  • Antigen: Substance that induces immune response
  • Cytokine: Signaling molecule in immune communication
  • Major Histocompatibility Complex (MHC): Molecules presenting antigens to T cells
  • Phagocytosis: Engulfment and digestion of pathogens by immune cells

16. Summary Table

Component Function Example
B cell Antibody production Plasma cell
T cell Cell-mediated immunity Helper T cell
Macrophage Phagocytosis, antigen presentation Kupffer cell (liver)
Dendritic cell Antigen presentation Langerhans cell
NK cell Kill virus-infected cells -

17. Further Reading

  • Abbas, A.K., Lichtman, A.H., Pillai, S. Cellular and Molecular Immunology (10th ed.)
  • Nature Immunology https://www.nature.com/ni/

18. Diagram: Immune Response to Infection

Immune Response

19. Quick Recap

  • Immune system = innate + adaptive arms
  • Recent tech (CRISPR, single-cell sequencing) is revolutionizing immunology
  • Environmental changes influence immune health
  • Memory trick: “B makes Bodies, T Targets”

End of Study Notes