Overview of the Immune System

Introduction to the Immune System

Introduction by Maria, Department of Immunology

Maria from the Department of Immunology introduces a series of lectures focusing on the immune system. The first lecture will provide a general overview, covering key components, while the second will delve into the immune system's functions.

Acknowledgement of Traditional Owners: Respect is paid to the Kulin Nation's people, the traditional owners of the land where the recording is made and viewed.

Lecture Topics

Over the two lectures, the following main topics will be covered:

• Introduction to the immune system, including features of innate and adaptive immunity

• Components of the immune system: cells, organs, and molecules

• Effector mechanisms of the immune system: how it eliminates microbes

Textbook References

Recommended textbook references for a general overview of the immune system:

• Chapter 43 of Campbell Biology

• Chapter one of Basic Immunology textbook (used for second-year immunology)

• Chapter one of Janeway's Immunobiology (used for third-year immunology unit)

Lecture Outcomes

By the end of this lecture, students should be able to:

• Outline the importance of the immune system in health and disease.

• Identify the broad classes of pathogens and describe the obstacles the immune system faces in providing protection against them.

• Compare and contrast key features of the innate and adaptive immune systems.

• Describe key components of the immune system, including cells, organs, and molecules.

The Importance of the Immune System

The immune system is vital for several reasons:

• Protection from disease

• Association with various diseases and disorders

• Basis for prevention and treatment strategies in diverse diseases, as well as in diagnostic and research applications

Protection from Disease

The immune system is the body's defense system against pathogens encountered daily.

• Protects against communicable and non-communicable diseases.

• Infectious diseases: viruses, fungi, bacteria (e.g., Plasmodium falciparum causing malaria), and helminths.

• Non-communicable diseases: Role in cancer surveillance and elimination of cancerous cells.

Involvement in Disease

The immune system is tightly regulated, and dysregulation can lead to disease. Types of immune-related diseases include:

• Autoimmune diseases: Inappropriate responses targeting self-tissues, such as rheumatoid arthritis (targeting joints), multiple sclerosis (targeting the nervous system), and type 1 diabetes (targeting beta cells in the pancreas).

• Allergies: Immune response to harmless environmental antigens, such as pollen exposure causing hives or food allergies.

• Inflammatory diseases: Such as inflammatory bowel disease, where an inflammatory response is mounted against commensal bacteria in the gut.

• Metabolic diseases: Obesity and associated inflammation leading to type 2 diabetes.

• Transplant rejection: Immune system recognizing a transplanted organ as foreign and attacking it.

• Cancer: Cancer cells evade the immune system, allowing tumor growth, or even exploit the immune system to their advantage.

• Immunodeficiencies: Failure or absence of parts of the immune system, as exemplified by David Vetter, who lived in a bubble due to a lack of T cells, or secondary immunodeficiencies caused by malnutrition or infections like HIV.

Immune System in Therapies, Prevention, Diagnostics, and Research

The immune system's function is harnessed for therapies, disease prevention, diagnostic, & research applications.

• Prevention and treatment strategies: Vaccination is the most well known, immunotherapies based on antibodies.

• Nobel Prize: Awarded to James Allison and Sasuku Honju for discovering that targeting inhibitory molecules can treat cancer.

• CAR T-cells: Another type of immunotherapy that kills cancer.

• Antibodies: Used targeting aspects and dampen down autoimmune responses.

• Diagnostic and research applications: Experimental techniques like flow cytometry, ELISAs, and point-of-care testing, such as pregnancy tests, COVID tests, and roadside drug testing.

Impact of Vaccines

Vaccines harness the immune system's function for our benefit. Vaccination involves giving a weakened or dead form of a pathogen, allowing us to mount an immune response. This forms memory responses that allow a quick response upon exposure to the real pathogen, preventing illness. This protects at an individual level by priming the immune system.

• Edward Jenner: Used cowpox in 1796 to immunize against smallpox.

• Herd immunity: Achieved when enough people are vaccinated, providing population-level protection by preventing easy spread of a virus.

• Measles vaccination: Introduction of the vaccine in the 1960s led to a decrease in deaths from measles infection.

• Outbreaks: Low vaccination rates can lead to outbreaks of disease, as seen with measles.

• Eradication of diseases: Smallpox has been eradicated due to vaccination, and polio is close to eradication.

• Vaccine controversy: Despite the enormous impact, vaccines can be a controversial topic with vaccine hesitancy.

Pathogens and the Immune System

Classes of pathogens the immune system must combat:

• Viral pathogens that live inside cells, such as the flu virus.

• Intracellular pathogens that live inside cells within vacuoles or vesicles, such as mycobacterium.

• Extracellular pathogens that live outside cells in the interstitial space or circulation.

• Parasitic worms.

Pathogens vary in size, from very small viruses to large worms visible to the naked eye. The immune system must combat all of these.

Routes and Sites of Infection

Microbes infect via various routes:

• Mouth and respiratory tract

• Gastrointestinal tract

• Cuts on the skin

They live in different sites:

• Outside the cell: In interstitial spaces, blood, on epithelial surfaces.

• Intracellularly: In the cytoplasm or in vesicular spaces.

• Viruses: Enter cells and use host cell machinery to replicate.

• Bacteria: Adhere to the surface of a host cell to infect it.

Mechanisms of Disease

• Direct damage to tissue: Pathogens produce toxins or have ways to kill cells.

• Immune response to pathogens: Can sometimes be the damaging effect.

• Toxins: Bacteria produce toxins that bind to receptors on cells, enter the cell, and kill it.

Immune system complexity

Recognizing and combating potential pathogens, considering their size, location, and infection methods, is complex. This recognition requires a complex system of different cells and molecules acting in an integrated manner. Innate and adaptive immune systems work together.