Introduction to Immunology

Introduction to Immunology

• Immunology is the study of immune responses, including cellular and molecular events that occur after an organism encounters microbes or foreign molecules.
• The immune system's main function is preventing or eradicating infections.
• Understanding the basic concepts, functions, and components of the immune system is crucial.

Learning Outcomes

• Understand the fundamental concepts and components of the immune system.
• Differentiate between innate and adaptive immunity.
• Identify the roles of immune cells (T cells, B cells, phagocytes) in defending against pathogens.
• Explain antigen recognition and immune response generation.
• Discuss the significance of immunologic memory for long-term protection.
• Analyze the relationship between immunity, disease (autoimmune disorders, immunodeficiencies), and public health.
• Understand the impact of immunization on disease prevention.

Immunity

• Immunity refers to resistance to pathogens and reactions to non-infectious substances, including harmless environmental molecules, tumors, and unaltered host components.
• Immunity is derived from the Latin word "immunitas," referring to protection, particularly from legal issues, granted to Roman senators.

Immune System-Immune Response

• The immune system comprises cells, tissues, and molecules that mediate reactions.
• The coordinated response constitutes the immune response.

Immune Warriors

• The immune system's major physiological function is preventing or eradicating infections.

Immunology

• Immunology is the study of immune responses, specifically the cellular and molecular events that occur post-exposure to microbes and other foreign substances.

Role of the Immune System - Implications

• Defense against infections: Deficient immunity increases susceptibility to infections (e.g., AIDS). Vaccines enhance immune defenses and protect against infections.
• Defense against tumors: Immunotherapy holds potential for cancer treatment.
• Tissue regeneration and scarring: The immune system repairs damaged tissue.
• Immune responses and disease: Immune responses cause allergic, autoimmune, and inflammatory diseases. Immune responses act as barriers to transplantation and gene therapy.

Stimulating Immune Responses

• Vaccines significantly reduce the incidence of various diseases. The provided table shows the historical decrease in disease cases following vaccination.

Host Defenses

• Host defenses are categorized into:
  • Innate immunity: Provides immediate protection against microbial invasion.
  • Adaptive immunity: Develops slowly but provides highly specialized defense against infections.

Innate Immunity

• Present in healthy individuals, ready to block microbe entry and eliminate succeeding microbes.

• The first line of defense is provided by epithelial barriers of skin and mucosal tissues, as well as cells and natural antibiotics present within the epithelia.

• If microbes breach epithelia, other innate components, such as phagocytes, innate lymphoid cells (ILCs), and plasma proteins (e.g., complement system), become involved.

• In addition to providing early defense against infections, innate immune responses are required to initiate adaptive immune responses against infectious agents.

Adaptive Immunity

• The adaptive immune system consists of lymphocytes with highly diverse, variable receptors for foreign substances and respective immune products like antibodies.
• Cells and molecules of the innate immune system recognize common microbial structures.
• Lymphocytes of the adaptive immune system recognize a wider variety of microbes' molecules and some non-infectious molecules.
• Any molecule recognized by lymphocytes or antibodies is called an antigen.
• Lymphoid and non-lymphoid cells (myeloid cells) are crucial components of the immune system.

Cells of the Immune System

• Lymphocytes: Adaptive immune response cells, recognizing antigens and differentiating into specialized defense cells.
• Antigen-presenting cells: Capture antigens to present to lymphocytes.
• Effector cells: Leukocytes that eliminate microbes, often lymphocytes but sometimes other leukocytes.

Tissues of the Immune System

• Specific tissues and organs (e.g., lymph nodes, spleen, bone marrow, blood, skin, intestines, liver, and lungs) contain defined numbers of lymphocytes.

Generative Lymphoid Organs

• T and B lymphocytes mature and become competent to respond to antigens in these organs.

Peripheral (Secondary) Lymphoid Organs and Tissues

• Lymph nodes, the spleen, and mucosal/cutaneous immune systems are organized to facilitate the development of adaptive immune responses.

Active vs. Passive Immunity

• Active immunity: Induced in an individual by infection or vaccination, the resulting response eradicates the infection and establishes resistance to future infections.
• Passive immunity: Confers immunity by transferring antibodies or lymphocytes from an actively immunized individual. This form of immunity may use antibodies synthesized with modern bioengineering techniques.

Adaptive Immunity: Humoral and Cellular

• Humoral immunity: Antibodies are produced by B lymphocytes, which target extracellular microbes and enhance phagocytosis.
• Cellular immunity: T lymphocytes target and eliminate infected cells, including intracellular microbes requiring cell-mediated activity.

Humoral Immunity

• Mediated by proteins, called antibodies, which are generated by B lymphocytes.
• Antibodies target extracellular microbes and enhance their uptake by phagocytes.
• Antibodies circulate throughout the extracellular fluids and lumens of mucosal organs (e.g., gastrointestinal and respiratory tracts) preventing antigens from invading tissue cells and neutralizing toxins produced by microbes.

Cell-mediated Immunity

• Defense against microbes already inside host cells, carried out by T lymphocytes.

B and T Cells

• T cells primarily recognize peptide fragments of protein antigens presented on cell surfaces, while B cells and antibodies recognize a broader range of molecules (proteins, carbohydrates, nucleic acids, lipids).

Memory

• Adaptive immune responses to repeated exposure to the same antigen are faster, larger, and more effective. This is due to immunologic memory.
• Immunological memory is a mechanism by which vaccines provide long-lasting protection.

Explore the foundational concepts of immunology, focusing on immune responses to pathogens and foreign molecules. Understand the roles of immune cells, the difference between innate and adaptive immunity, and the importance of immunologic memory. This quiz will help you analyze the intersection of immunity, disease, and public health.