Overview of the Immune System

Chapter 1: Overview of the Immune System

Immunology

Course: BIOL4408/5402
Instructor: Emelyn Salazar, PhD
Institution: Texas A&M University, Kingsville

The Immune System

  • Evolution: The immune system has evolved over time to protect multicellular organisms from pathogens and other threats.

  • Complexity: It is a complex and dynamic network of cells, molecules, and mechanisms that work together to recognize and eliminate foreign cells and damaged cells.

  • Presence: Elements of the immune system can be found throughout the plant and animal kingdoms, being highly evolved in mammals.

Key Definitions

  • Immunis: Origin of the word meaning "exempt"; the concept of immunity relates to a state of protection against foreign pathogens or substances (antigens).

  • Homeostasis: The immune system has a key interplay with other systems to guarantee homeostasis (equilibrium).

A Historical Perspective of Immunology

Early Writings and Discoveries

  • Thucydides (430 BC): Recorded the survival of individuals during the plague of Athens, suggesting they could nurse the ill.

  • China (10th Century): Early immunization practiced using crusts of smallpox lesions.

  • Rhazes (1000 AD): Discovered allergic asthma and the theory of acquired immunity.

Important Figures

  1. Emil von Behring & Shibasaburo Kitasato: Developed theories on passive immunity.

  2. Louis Pasteur & Emile Roux: Induced acquired immunity using an attenuated culture in chickens; created vaccination techniques.

  3. Ilya Mechnikov: Proposed the cellular theory of immunology.

  4. Robert Koch: Contributed to the understanding of delayed-type hypersensitivity.

Date timeline of key contributions from various scientists spans from 2000 BC to the late 20th century, with significant milestones including the introduction of variolation, the establishment of antibody theory, and advancements in transplantation immunology.

Important Historical Milestones in Immunology

  • 1700s to 1900s: Development of variolation and vaccination methods by Edward Jenner and others.

  • 1860s to 1880s: Establishment of the germ theory by Louis Pasteur and the development of vaccines against diseases like rabies and anthrax.

  • Modern Immunology: Involves advances in understanding immune responses including T and B lymphocytes, the creation of monoclonal antibodies, and breakthroughs in gene therapy and immunotherapy.

Vaccination and Its Impact

  • Vaccination Importance: Can generate immunity without causing disease, preparing the immune system to eradicate infectious agents before they can cause illness.

  • Historical Examples:

    • Rabies Vaccine:

    • Smallpox Eradication: Exemplifies the impact of vaccines on public health.

Vaccine Controversy

  • Concerns raised by opponents claiming vaccines cause harm, citing a retracted study linking the MMR vaccine to autism, which has been debunked.

  • Vaccination is viewed as both a personal health choice and a public health obligation.

Epidemiological Data on Diseases

Table 1-1: Cases of Selected Infectious Diseases in the U.S. (Pre- and Post-Vaccine)

  • Smallpox: 48,164 cases pre-vaccine → 0 post-vaccine.

  • Diphtheria: 175,885 cases pre-vaccine → 2 post-vaccine.

  • Measles: 503,282 cases pre-vaccine → 79 cases in 2016; significant increase in 2019.

Additional Factors in Infection Prevention

  • Role of a healthy environment, hygiene, and nutrition in preventing infections.

  • Antibiotics: Used to combat bacterial infections; however, antibiotic resistance poses significant challenges.

Components of Immunity

Humoral Immunity

  • Concept established by Emil von Behring and Shibasaburo Kitasato, which combats infectious agents using antibodies produced by B lymphocytes (B cells).

  • Antisera (antibody-containing serum fractions) can be used therapeutically.

Cellular Immunity

  • Phagocytosis: Demonstrated by Elie Metchnikoff; white blood cells engulf pathogens.

  • Two types of lymphocytes:

    • B Lymphocytes (B cells): Produce antibodies (humoral).

    • T Lymphocytes (T cells): Involved in cell-mediated responses (e.g., killing infected cells).

Immunity Types

Active vs. Passive Immunity

  1. Passive Immunity: Transfer of protection via antiserum, maternal antibody transfer.

  2. Active Immunity: Immunity derived from the body’s direct production through vaccination or infection.

Clonal Selection and Immunological Memory

  • Clonal Selection Theory: Each lymphocyte expresses a unique receptor, proliferating upon antigen binding, creating a specific immune response.

  • Immunological Memory: Primary and secondary responses display rapid and effective reactions upon subsequent exposures to antigens, a hallmark of adaptive immunity.

Immune Dysfunction

  • Immune responses can lead to:

    • Hypersensitivity (e.g., allergies)

    • Autoimmune Diseases (e.g., lupus, multiple sclerosis)

    • Immunodeficiency: Results in increased susceptibility to infections.

The Role of the Microbiome

  • Commensal organisms contribute to immune balance; dysbiosis can lead to inflammation and other immune-related conditions.

Special Circumstances

Tissue Transplants

  • Immune response against transplant tissues necessitates strategies to minimize rejection.

Cancer Immunology

  • Cancer cells can evade detection by the immune system, making it challenging to initiate an immune response against them.

Summary

  • Complex Nature of Immunity: The interplay between various immune components and their roles in infection prevention, treatment, and maintaining health is essential for understanding both basic and advanced biomedical science.