Immunology Basics Quiz

Introduction to Immunology

• Immunology is the study of all aspects of host defense against infection and the adverse consequences of immune responses.
• It explores mechanisms to neutralize, metabolize, or eliminate foreign material without harming the host tissue.
• Immunology investigates the cellular and physiological mechanisms that allow the body to recognize foreign materials.
• This includes physical barriers, protective chemicals, and specialized cells for self/non-self recognition (homeostasis).
• Immunity is the body's ability to resist or eliminate potentially harmful foreign materials or abnormal cells.
• Immune responses include defense against pathogens and noxious chemicals.
• Removal of worn-out cells and tissue debris are part of the process.
• Identifying and destroying abnormal/mutant cells (like in cancer) and rejecting foreign cells (organ transplants) are other immune responses.
• Maintaining homeostasis is also part of immunity.
• Inappropriate immune responses, like allergies and autoimmune diseases, are also studied.

Immune System

• The immune system is a complex system that involves multiple body structures to defend against pathogens and cancer.
• It has the ability to generate a wide variety of cells and molecules.
• These cells specifically recognize and eliminate a large range of foreign invaders.
• The immune responses are collective and coordinated, responding to the introduction of foreign substances in body tissues, cells, and molecules.

Principles of Immune Responses

• Recognition: Identifying self vs. non-self/ danger vs. non-danger.
• Response: Appropriate and specific responses to pathogens, developing progressively after exposure, and being rapid.
• Memory: Secondary infections are faster and stronger.
• Regulation: Immune response must be downregulated after a pathogen is eliminated to avoid chronic inflammation or autoimmune diseases.

Roles of the Immune System

• Protecting against pathogens, including intracellular (viruses, some bacteria, parasites), and extracellular (most bacteria, fungi, parasites) pathogens.
• Rejecting foreign cells (foreign organs).
• Identifying and eliminating modified or altered self-cells, for example, tumor cells.
• Protecting from environmental stimulants (toxins, allergens).
• Maintaining homeostasis.
• Destroying abnormal, infected, or dead cells through apoptosis (programmed cell death).
• Removing worn-out cells (like old red blood cells) and tissue debris from injuries or diseases.

Source of Exposure

• Microorganisms, allergens, parasites, malignant cells, and toxins are sources of exposure.
• The body utilizes various defense mechanisms like skin, mucosal immunity, lysozyme, phagocytes, and immunoglobulins to deal with these exposures and maintain host resistance.

Response to Infection

• Innate immunity (0-4 hours): Non-specific pre-formed effectors remove infectious agents.
• Early induced response (4-96 hours): Effector cells recruitment, antigen transport to lymphoid organs, and effector cell activation.
• Late adaptive response (>96 hours): Naive B and T cell recognition and activation, clonal expansion and differentiation of effector cells.
• Protective immunity: Pre-formed antibody and effector cells remove infectious agents.
• Immunological memory: Memory B and T cells quickly respond to previously encountered pathogens.

Historical Perspective

• Past widespread plagues (like Athenian Plague, Black Death) highlighted the importance of the immune response.
• Ancient practices like variolation, a form of deliberately inducing smallpox, were used.
• Edward Jenner's discovery of cowpox vaccination against smallpox was a significant advancement, setting the stage for vaccines.

Observing Recovered Patients

• Observation of recovered patients from plagues like the Athenian Plague.
• Early forms of variolation, including inhalation of smallpox scabs, were used.

Vaccine

• A vaccine is a preparation of microbial antigen often combined with adjuvants, to induce protective immunity against infectious diseases.
• Vaccines are derived from attenuated or weakened pathogens.
• Smallpox was eradicated globally due to vaccination programs.

Lymphoid System and Immune Cells - Lesson Objectives

• Define lymphoid organs and tissues.
• Describe types of lymphoid organs and tissues.
• Describe the immune system cells.

Lymphoid System and Immune Cells - Details

• A system coordinating antigen, exosome, and lymphocyte migration from peripheral tissues to collecting vessels (e.g., lymph nodes).
• Primary lymphoid organs (bone marrow, thymus): Origin and maturation of blood cells including WBCs, RBCs, platelets.
• Bone marrow: Hematopoiesis occurs here primarily in flat bones (sternum, vertebra, hip bones), where stem cells differentiate into leukocytes and lymphocytes.
• IL-3 produced in the bone marrow stimulates granulocyte and monocyte formation.
• Interleukin-7 is produced by marrow stromal cells which stimulate B-cell maturation from precursor cells.
• Hematopoiesis: Blood cell formation in developing embryos starts with blood islands in the yolk sac and later shifts to the spleen, liver, and lymph nodes. For adults, it primarily occurs in the pelvis, cranium, vertebrae, and sternum.
• The thymus: Bilobed organ in the upper anterior thorax (above the heart). It has a cortex with a high density of pre-T lymphocytes, and a medulla with fewer lymphocytes. The thymus plays a key role in T-lymphocyte development and maturation. The organ also undergoes physiologic involution with aging.

Secondary Lymphoid Organs

• Spleen: Large, ovoid organ in the left upper abdominal cavity filtering blood and trapping pathogens.
• Mounts immune responses against blood-borne antigens.
• Red pulp: Removes old and defective red blood cells.
• White pulp: Contains lymphocytes, like T cells and B cells, involved in immune responses to blood-borne antigens.
• Lymph Nodes: First organized lymphoid tissue encountering antigens that enter from tissues.
• Sites where immune responses to antigens in lymph are mounted.
• Cortex: Has lymphocytes, macrophages, and follicular dendritic cells (mostly B cells).
• Paracortex: Rich in T lymphocytes and interdigitating dendritic cells.
• Medulla: Filled with plasma cells actively secreting antibodies.
• Tonsils: Collections of lymphoid tissue in the mouth (aerodigestive tract), helping protect against respiratory and gastrointestinal infections. Contains B and T cells that fight infection; produces antibodies against Polio, Streptococcal pneumonia, Influenza, and various other infections.
• MALT (Mucosa-Associated Lymphoid Tissue): Includes GALT (gut-associated lymphoid tissue), BALT (bronchial-associated lymphoid tissue), and UALT (urogenital-associated lymphoid tissue), localizing immune responses at mucosal surfaces, composed of lymphocytes and antibodies.
• Peyer's Patches: Specialized lymphoid follicle in the intestine, crucial for immune responses against intestinal antigens. Contains M cells and richer in B cells.
• Appendix: A blind-ended tube connected to the cecum, that is rich in lymphoid tissue (similar to Peyer's patches) possibly having a role in controlling bacterial populations in the intestines.

Cutaneous-Associated Lymphoid Tissue (CALT)

• Epithelial cells (keratinocytes) of the skin produce cytokines which induce local inflammatory responses.
• Keratinocytes express MHC class II and function as antigen presenting cells.
• Langerhans cells migrate from epidermis to regional lymph nodes and differentiate into interdigitating dendritic cells.

Tertiary Lymphoid Tissues (TLTs)

• Localized lymphoid tissues which form during persistent inflammation, infection, or allograft.
• Important for containing chronic immune responses, microbial infections, autoimmune disease, and allograft responses.
• Contain APCs (antigen presenting cells) like dendritic cells and follicular dendritic cells, as well as T and B cells within distinct compartments.

Cells of the Immune System

• Hematopoiesis: Process of blood cell formation from pluripotent hematopoietic stem cells (HSCs).
• HSCs reside in hematopoietic tissues (like the liver and bone marrow).
• Differentiation of cells occurs through myeloid and lymphoid lineages (producing lymphocytes).
• Specific categories like granulocytes (neutrophils, basophils, eosinophils) and agranulocytes (monocytes/macrophages, dendritic cells, lymphocytes) are present and have various functions.

Cell Types (Granulocytes / Agranulocytes)

• Granulocytes: Contain granules (visible in a light microscope after staining).
• Neutrophils, basophils, eosinophils are granulocytes.
• Agranulocytes: Do NOT contain granules visible under a light microscope after staining
• Monocytes/Macrophages, Dendritic cells, and lymphocytes are agranulocytes.

Neutrophils

• Multilobed nucleus (1-6 lobes).
• Key effector cells of the innate immune response.
• Live a few days and circulate in blood.
• Function in phagocytosis and response to inflammation; involved in fever/ releasing fever producing substances.

Eosinophils

• Bi-lobed nucleus.
• Constitute 1-3% of circulating leukocytes.
• Important for killing antibody-coated parasites.
• Have functions in mild phagocytosis, parasitic infection control, and allergic responses.

Basophils

• <1% of leukocytes. Characterized by an S-shaped (kidney) nucleus obscured by coarse blue granules.
• Functions in phagocytosis, inducing inflammatory responses, releasing histamine and other chemical mediators, and increasing blood vessel permeability.

Mast Cells

• Unilobe nucleus.
• Less than 1% of all leukocytes.
• Primarily reside in tissues near blood vessels, and contain many granules filled with mediators
• Involved in immediate hypersensitivity reactions, tissue repair, and defense against pathogens.

Monocytes/Macrophages

• Monocytes: Circulate in blood, mature into macrophages in tissues.
• Phagocytosis of dead cells and pathogens.
• Produce reactive oxygen species (ROS) to destroy pathogens.
• Important immune surveillance cells.

Dendritic Cells

• Irregular/branching/dendritic shaped cell bodies.
• Involved in antigen presentation.
• Activate naïve T cells.

Natural Killer (NK) Cells

• Large granular lymphocytes.
• 5-15% of human peripheral blood leukocytes.
• Spherical in shape and have lytic granules, secretory lysosomes.
• Recognize cells with abnormal/reduced MHC class I markers and kill those targets via apoptosis induction.

B Cells

• Mature in bone marrow and migrate to lymphoid tissues.
• Involved in antibody-mediated immunity.
• Provide memory response to antigens.

T Cells

• Immature lymphocytes mature in the thymus and migrate to lymphoid tissues.
• Involved in cell-mediated immunity.
• Provide memory responses that establish tolerance to innocuous foreign antigens.

Cytokines

• Small, secreted proteins, used as communication molecules to mediate cell-to-cell interactions and modulate immune responses.

• Induce effects through autocrine, paracrine, and endocrine modes.

• Diverse effects/ functions including: mediating natural immunity, regulating lymphocyte growth, activating inflammatory cells, regulating leukocyte movement, and stimulating hematopoiesis.

• Classified by structure (e.g., hematopoietins, interferons, TNF superfamily, chemokines).

• Classified by function (e.g., regulating immune responses, initiating inflammatory reactions, coordinating cellular behavior).

• Properties include pleiotropy, redundancy, synergism, and antagonism.

Test your knowledge on the fundamental concepts of immunology, including the functions of the immune system, immune responses, and historical milestones in vaccine development. This quiz will challenge your understanding of key terms and principles that govern immunological science.