Immunology

Introduction to the Immune System

• The immune system is a complex network of cells and processes that protect the body against infection by pathogenic microorganisms.
• Pathogens invade the body, disrupting homeostasis and causing illness.
• Pathogens, such as bacteria, viruses, fungi, and protists, can cause various diseases.

Types of Pathogens

• Bacteria are single-celled prokaryotic organisms.
  • Average size: 0.5-5µm (micrometers)
• Viruses are smaller than cells and lack cellular components.
  • Composed of a strand of DNA or RNA surrounded by a protein coat.
• Fungi are eukaryotic organisms, typically multicellular, with thread-like structures called hyphae.
  • Average size: 5-50µm (micrometers)
• Protists are eukaryotic single-celled or simple multicellular organisms.
  • Average size: 1-2mm (micrometers/nanometers)
• Prions are misfolded proteins that can cause disease in humans and animals.
• Parasites are organisms that live on or in another organism, known as their host, and obtain resources from it.

Pathogens Cause Disease

• Pathogenic microorganisms are those that can cause disease.
• The top 5 communicable diseases globally vary depending on factors like time and location.

How Diseases Spread

• Transmission of diseases occurs through different methods.
  • Direct contact: HIV, malaria (physical touch, bodily fluids)
  • Indirect contact: touching an object touched by an infected person
  • Inhalation: pathogens transmitted through coughs or sneezes
  • Inoculation: introducing a small amount of inactive pathogen to stimulate immune response
  • Ingestion: contaminated food or water
  • Vectors: living organisms that carry pathogens between organisms

Reservoirs

• These are sources of infection, such as soil, animals, water, or other environments that contain microorganisms.
• Example: tetanus, where soil is the reservoir for the bacteria.

Fomites

• These are non-living objects that can contaminate with pathogens.
  • Examples: door handles, medical instruments

Asymptomatic Carriers

• Individuals carrying a disease without displaying symptoms.
• Carry risks of spreading the disease, unknowingly.

Vectors

• Living organisms that transmit pathogens between organisms.
• Examples: mosquitoes, ticks, fleas, and aquatic snails.
• Diseases carried by these vectors: malaria, dengue fever, yellow fever, Lyme disease.
• Body lice transmit typhus fever

Other Organisms Contributing to Disease

• Prions are misfolded proteins that cause various neurodegenerative diseases.
• Parasites harm hosts but typically don't kill them. -Example: Toxoplasmosis

The Immune Response

• The immune system protects the body against infection through:
  • Non-specific defenses: skin, mucous membranes, phagocytosis, inflammation
  • Specific defenses: T cells, B cells

Key Definitions

• Antigen: Molecules that trigger an immune response (from pathogens or other sources)
• Antibodies: Proteins produced by B cells to target specific antigens.

White Blood Cells

• White blood cells (leukocytes) are crucial parts of the immune system, defending against pathogens.
• Different types, each with specific jobs.

Phagocytes and Lymphocytes

• Phagocytes: cells that engulf and destroy pathogens.
  • Make up approximately 75% of white blood cells.
• Lymphocytes (include T and B cells): cells involved in specific immune responses. - Unique immune response to each antigen.

Innate Immunity

• A non-specific immune response involving general defenses, such as phagocytosis and inflammation.
• Effective against a wide range of pathogens.

Adaptive Immunity

• A specific immune response targeting particular pathogens through the production of specialized cells (like T and B cells).
• Takes time to develop compared to innate immunity.
• T cells and B cells contribute to a secondary immune response, giving immunity to subsequent encounters with the same pathogen.

Inflammation

• A localized response to injury or infection that involves increased blood flow and chemical release.
• Aids in delivery of immune cells to affected site
• Promotes phagocyte activity
• Creates swelling due to fluid leakage.

The Lymph System

• A network of vessels and organs, complementing the cardiovascular system, crucial to immune function.
• Involved in immune response (filters body fluids).

Thymus

• Plays a vital role in the development and maturation of T lymphocytes.

Viral Replication

• Viruses require host cells to replicate.
• Follows a typical life cycle from attachment, entry, replication, assembly, and release.

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