Introduction to Immunology

Introduction to Immunology

Learning Objectives

By the end of this lesson, students will be able to:

• Describe concepts related to immunology:

  • Immunology

  • Immunity

  • The immune system

  • Immune response

• Describe the importance of the immune system for health.

• Name the main organs and cells of the immune system.

• Recognize basic immune cells and their functions.

• Appreciate the similarities and differences between human and animal immune systems.

• Describe the immune system in various animal species.

Glossary of Common Immunology Terms

1. Basic Immune System Terms

   • Immunity: The body’s ability to protect itself from disease.

   • Pathogen: Agents causing disease, including bacteria, viruses, fungi, and parasites.

   • Antigen: A substance triggering an immune response, often part of a pathogen.

   • Antibody: A Y-shaped protein that binds specifically to an antigen.

   • Immune response: The immune system's reaction to an antigen.

Cells of the Immune System

• Red Blood Cells (Erythrocytes):

  • Recent research suggests RBCs actively modulate the innate immune system.

• White Blood Cells (Leukocytes):

  • Defend the body against pathogens. Include:

  • Monocytes and Lymphocytes

  • Neutrophils

  • Eosinophils

  • Basophils

  • Lymphocytes:

    • Involved in specific immunity.

    • B cells: Produce antibodies.

    • T cells: Help or kill infected cells.

    • Helper T cells (CD4⁺): Activate other immune cells.

    • Cytotoxic T cells (CD8⁺): Kill infected or abnormal cells.

  • Phagocytes:

    • Cells that engulf and digest pathogens (e.g., macrophages).

    • Macrophage: A large phagocyte that activates other immune cells.

Immune Responses

• Innate Immunity:

  • Immediate, non-specific defense mechanism including skin and inflammation.

• Adaptive Immunity:

  • Specific, long-lasting defense involving B and T cells.

• Humoral Immunity:

  • Antibody-mediated immunity provided by B cells.

• Cell-mediated Immunity:

  • Immunity involving T cells.

• Memory Cells:

  • Long-lived cells enabling faster response upon re-exposure to the same antigen.

Types of Immunity

• Active Immunity:

  • Produced by the body after infection or vaccination.

• Passive Immunity:

  • Antibodies received from another source (e.g., maternal antibodies to newborn).

• Vaccination:

  • Exposure to a harmless form of an antigen to build immunity.

Immune Disorders

• Allergy:

  • Excessive immune response to harmless antigens.

• Autoimmune Disease:

  • Immune system mistakenly attacks the body’s own cells.

• Immunodeficiency:

  • Weakened immune response due to illness or genetics.

Other Key Terms

• Inflammation:

  • Redness, swelling, heat, and pain due to immune activity.

• Cytokines:

  • Chemical messengers coordinating immune responses.

• Complement System:

  • Proteins assisting antibodies in pathogen destruction.

• MHC (Major Histocompatibility Complex):

  • Molecules displaying antigens to T cells (MHC class I and II).

• Transplantation:

  • Transfer of organs, tissues, or cells.

• Immunological Tolerance:

  • The immune system's ability to avoid attacking its own cells.

What is Immunology?

• Immunology: A branch of biology and medicine that studies immune systems across all organisms.

  • In veterinary medicine, focuses on:

  • Functioning of immune systems in animals.

  • How animals defend against infections and diseases.

  • Recognition of foreign substances by the body.

What is Immunity?

• Immunity: The state of resistance to a specific pathogen, aiding the body to:

  • Prevent infection.

  • Effectively fight disease.

• Types of Immunity:

  • Natural: Gained after infection.

  • Artificial: Gained through vaccination.

What is the Immune System?

• Immune System: A complex defense network consisting of:

  • Cells: Mainly white blood cells.

  • Tissues: Such as lymph nodes and spleen.

  • Molecules: Including antibodies and cytokines.

• Functionality: All components collaborate to protect the body from pathogens.

Immune System Against Non-Pathogens

• The immune system reacts to non-pathogenic substances (e.g., environmental antigens or self-components), which can lead to:

  • Tolerance: Safe coexistence with harmless substances.

  • Allergy: Misguided defense against harmless substances.

  • Autoimmunity: Attack on self-components.

Immune Response Mechanism

• Trigger: Identification of a foreign antigen.

• Mechanism:

  1. Recognition of antigen.

  2. Activation of immune cells.

  3. Production of antibodies and lymphokines.

  4. Elimination of the pathogen.

Organs of the Immune System

• Tonsils and adenoids

• Lymph nodes

• Lymphatic vessels

• Thymus

• Appendix

• Spleen

• Peyer's patches

• Bone marrow

Comparison of Immune System in Animals and Humans

• Similarities:

  • General immune functionality is conserved across species, particularly vertebrates (e.g., macrophages, neutrophils, B cells, T cells).

  • Pigs, for example, exhibit an 80% similarity in immune system structure and function compared to humans (Dawson, 2011).

Specifics of Animal Immune Systems

• Pigs as Model Organisms:

  • Used for studying human immunological diseases due to similarities in physiology and immune function.

  • Advances research in transplantation immunology, vaccines, and infectious disease responses.

Avian Immune Organs and Their Functions

1. Harderian Gland:

   • Location: Orbit of chicken, behind the eyes.

   • Function: Produces tears and aids in immune defense around the eyes.

2. Thymus Gland:

   • Location: Neck of birds.

   • Function: Produces and matures T lymphocytes.

3. Bursa of Fabricius:

   • Unique to birds.

   • Primary lymphoid organ for B cell differentiation and maturation.

4. Cecal Tonsils:

   • Location: Junction of cecum and rectum.

   • Function: Largest lymphoid collections in avian gut-associated lymphoid tissue (GALT) that provide protective immune responses against intestinal pathogens.

Immune System of Ostriches

• Ostriches possess the most vigorous immune system among land animals;

  • Researchers, such as Professor Yasuhiro Tsukamoto, discovered potent antibodies in ostrich yolk.

  • Ostriches can produce antibodies within two weeks of antigen exposure; their IgY antibodies have greater stability compared to other avian IgY.

Fish Immune System

• Both cartilaginous and bony fish can mount adaptive immune responses and possess a complete set of lymphoid organs, except for bone marrow.

• Most bony fish carry out hematopoiesis in the spleen, kidney, intestinal submucosa, and thymus as a substitute for functional bone marrow.

Similarities Between Human and Animal Immune Systems

Differences Between Human and Animal Immune Systems

Aims of Immunology

• Understand immune system functions, including:

  • Detection and response to external invaders.

  • Maintenance of tolerance to self-cells and tissues.

Inflammation

• Defined as the body’s response to injury, infection, or irritation with five basic signs:

  • Redness

  • Swelling

  • Heat

  • Pain

  • Loss of function

Fever as an Immunological Response

• Fever: A defense mechanism characterized by an elevated body temperature above normal during illness or infection.

  • Mechanism:

  1. Trigger: Pathogens or damaged cells release pyrogens (e.g., bacterial toxins, IL-1, IL-6, TNF-α).

  2. Hypothalamus Activation: Pyrogens stimulate hypothalamus to raise normal body temperature.

  3. Response Strategies:

     • Shivering to generate heat.

     • Vasoconstriction to minimize heat loss.

     • Behavioral changes, such as seeking warmth.

Effects of Fever

• Fever serves as a protective mechanism by:

  • Inhibiting microbial growth: Higher temperatures hinder pathogen replication.

  • Enhancing immune function: Stimulates activity of immune cells for better pathogen recognition and destruction.

  • Accelerating healing: Speeds up metabolic processes necessary for tissue repair, aiding recovery from infection or injury.

Current Research Trends in Immunology

• Immunogenomics: Investigating pig immune genes and pathways using high-throughput sequencing.

• Mucosal Immunity: Studying immunity in gut, respiratory, and reproductive tracts for implications in disease resistance.

• One Health Approach: Analyzing zoonotic pathogens and their immune interactions in pigs, with relevance to both veterinary and human health.

Nobel Prizes in Immunology**