Introduction to Immunology

Introduction to Immunology

• Immunology is the study of immune responses and cellular/molecular events in response to microbes and foreign molecules.
• The immune system's primary function is to prevent or eliminate infections.

Learning Outcomes

• Understand the basic concepts of the immune system, including its functions and components.
• Identify the differences between innate and adaptive immunity.
• Describe the roles of immune cells (T cells, B cells, phagocytes) in pathogen defense.
• Explain antigen recognition and immune response generation.
• Discuss the importance of immunological memory and its role in long-term protection.
• Explore the relationship between immunity and disease (autoimmune disorders, immunodeficiencies).
• Analyze the impact of immunization on public health and disease prevention.

Immunity

• Latin origin: "immunitas" - protection of Roman senators.
• Resistance to pathogens.
• Reactions to non-infectious substances (harmless environmental molecules, tumors, or even unaltered host components) are also considered immunity.

Immune System-Immune Response

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

Immunology Definition

• The study of immune responses to microbes and other foreign materials.

Role of the Immune System Implications

• Defense against infection: Inadequate immunity leads to increased susceptibility to infections (e.g., AIDS). Vaccination strengthens immune responses.
• Defense against tumors: There is potential for immunotherapy.
• Control of tissue regeneration and scarring: Repair of damaged tissues.
• Immune system's role in injury and inflammation: Immune responses can cause inflammation (e.g. allergic, autoimmune diseases).
• Transplantation and gene therapy: The immune system acts as a barrier.

Stimulating Immune Responses Through Vaccination

• Charts detail the maximum number of cases and cases in 2014 for various diseases (e.g., diphtheria, measles, mumps, pertussis, polio, rubella, tetanus, Hemophilus influenzae type B infection, Hepatitis B).

Host Defenses

• Innate immunity provides immediate protection against microbial invasion.
• Adaptive immunity develops protection more slowly but provides specialized defense mechanisms.

Innate Immunity

• Present in healthy individuals.
• Designed to block the entry of microbes and quickly eliminate invading microbes.
• First line of defense: epithelial barriers (skin and mucosal tissues), cells, and natural antibiotics in epithelia.
• If microbes penetrate the epithelial barriers, other innate components like phagocytes (e.g., macrophages), innate lymphoid cells (ILCs), and plasma proteins (e.g., complement system) take over.
• Innate immunity is required to trigger adaptive immune responses against infectious agents.

Adaptive Immunity

• Lymphocytes with highly variable receptors recognize foreign materials.
• The resulting products (e.g., antibodies) and cells target specific foreign substances.
• Cells and molecules of innate immunity recognize structures shared by microbes' classes.
• Adaptive lymphocytes recognize a wider variety of molecules (microbes and non-infectious).
• Any molecule specifically recognized by lymphocytes or antibodies is an antigen.
• Lymphocytes and non-lymphoid cells (e.g., myeloid cells).
• Cells and components of the immune system (B cells and T cells, macrophages)
• Bone marrow is the source for hematopoiesis (production of blood cells) including lymphocytes.
• Adaptive immunity depends on specialized response mechanisms (different cells and molecules for intracellular and extracellular microbes).

Humoral Immunity

• Antibodies mediate humoral immunity.
• B lymphocytes produce antibodies.
• Antibodies target extracellular microbes.
• Antibodies enhance the uptake and elimination of extracellular microbes by phagocytes.
• Antibodies circulate in fluids (tissue fluids, mucosal organs).

Cell-Mediated Immunity

• T lymphocytes mediate cell-mediated immunity.
• T cells target microbes that have entered host cells.
• Specialized T cell types eliminate intracellular microbes (killer T cells) and coordinate the response involving other cells (helper T cells)
• B and T cell specificities differ; T cells mostly recognize peptide fragments of proteins presented on cell surfaces. 
• B cells and antibodies recognize numerous molecules (proteins, carbohydrates, nucleic acids, and lipids).

Memory

• Adaptive immune system creates immunological memory.
• Faster, larger, and more effective responses to repeated exposures to the same antigen.
• Vaccines rely on this principle to provide long-lasting protection.

Active vs. Passive Immunity

• Active immunity: Immunity in an individual who is exposed to the antigens of a microbe and mounts a response, resulting in resistance to that microbe.
• Passive immunity: Immunity conferred on a naive individual by transfer of antibodies or lymphocytes (often from actively immunized individuals) to provide resistance; using modern bioengineering.

Cells of the Immune System

• Lymphocytes: Adaptive immunity cells; recognize antigens and develop into defense function cells.
• Antigen-presenting cells: Cells that capture antigens and display them to lymphocytes.
• Effector cells: Leukocytes (white blood cells) that eliminate microbes ("effectors" of the immune response); may be lymphocytes or other leukocytes.

Tissues of the Immune System

• Lists specific tissues (e.g., tonsils, thymus, lymph nodes, spleen, bone marrow, blood, skin, intestines, liver, lungs).
• Provide approximate lymphocyte counts.

Generative Lymphoid Organs

• Sites (e.g., bone marrow, thymus) where immune cells develop/mature.

Peripheral (Secondary) Lymphoid Organs and Tissues

• Areas (e.g., lymph nodes, spleen, mucosal and cutaneous immune systems) where lymphocytes interact and mount responses to antigens.

Explore the basics of immunology, including the functions and components of the immune system. This quiz covers innate and adaptive immunity, immune cell roles, antigen recognition, and the significance of immunological memory. Additionally, it addresses the relationship between immunity and diseases, alongside the role of immunization in public health.