Immune System Vocabulary Flashcards
Immune system: a dynamic, layered defense
Immune components are diverse regulators: proteins, signals, and effector molecules that communicate and move around the body; the system is a fluid, mobile network similar to players in a sport. Metaphors used in lecture: immunology as war, policing, and sports; understanding comes from watching how the game unfolds, not just listing positions.
To understand the immune system, you need an integrated view rather than a single snapshot. Analogy used: explaining football to someone who has never seen it—start with players, then what they can do, then example plays (not exhaustive), so you can root for a team (Team Wide: the immune system).
In science communication, systems are often categorized into layers. The immune system is described here in three helpful layers (defense tiers): barriers, innate (nonspecific) defenses, and antigen-specific (adaptive) defenses.
Emphasis on categories: grouping similar/different components helps organize understanding of the immune landscape.
Layer 1: Barriers (the first line of defense)
Barriers are not just walls; they are dynamic barriers comprising:
Skin
Mucosal surfaces (e.g., mucous membranes)
Chemicals and fluids produced at surfaces
Primary functions of barriers:
Kill or inhibit microbes at entry points
Slow down or limit microbial growth
Prevent movement of microbes from surface into tissues
Barriers are active and dynamic, not just static walls; they can regulate microbial access and movement.
Layer 2: Innate immune response (inside the tissues, the quick responder)
Innate immunity is the immediate, non-specific response ready from birth and generally doesn’t change much with time.
Innate components include cells and molecules that respond rapidly to infection:
Cells:
Neutrophils (a major granulocyte; part of granulocytes; often the first responders)
Macrophages (big eater; derived from monocytes)
Monocytes (white blood cells in blood that differentiate into macrophages when they exit blood vessels)
Dendritic cells (key for communication with the adaptive layer; part of innate defense and antigen presentation)
Natural killer (NK) cells (kill compromised host cells and produce cytotoxic factors)
Other early-infection molecules:
Defensins (peptides produced by various cells; inhibit bacterial growth; part of barrier defense but active in innate response)
Interferons (proteins that interfere with viral replication; antiviral defense)
Cytokines (a broad, diverse family of signaling molecules that coordinate immune responses)
Complement proteins (a group of blood proteins that help fight infection; most effective when infection reaches the bloodstream; activity is limited at skin surfaces before vascular involvement)
Key ideas about innate immunity:
It responds to pathogens quickly but does not adapt or learn from exposure in the way the adaptive system does.
Innate responses do not become stronger with subsequent infections in a way that increases the baseline of innate components; aging and factors like diet can modulate the level of innate components, but prior infection doesn’t create lasting enhanced innate immunity.
Innate responses are non-specific but essential for immediate defense and for shaping subsequent adaptive responses.
Functional notes on specific innate cells:
Neutrophils: fast, phagocytic eaters; part of the granulocyte family (PMNLs — polymorphonuclear leukocytes).
Macrophages: large phagocytes derived from monocytes; also key in signaling and antigen presentation.
Dendritic cells: strong communicators; bridge innate and adaptive immunity by presenting antigens to T cells and shaping the adaptive response.
NK cells: detect and kill cells that have become stressed or altered (e.g., infected or transformed); can detect via different recognition mechanisms than T cells.
Antimicrobial molecules and their targets:
Defensins: inhibit bacteria (antibacterial peptides).
Interferons: antiviral defense; part of early innate response.
Innate defense signaling and coordination:
Cytokines: diverse signaling molecules with numerous roles; many cytokines exist, and the field includes more types than can be memorized easily.
Early defense limitations:
If a microbe breaches barriers, innate components are deployed immediately from within tissue to contain infection and alert other immune parts.
Layer 3: Antigen-specific (adaptive) immune response (tailored, memory-forming defense)
The adaptive immune response is antigen-specific and capable of learning; it changes with exposure and can provide memory for more efficient future responses.
Key concepts:
Antigen: a foreign molecule or part of a molecule that can trigger an immune response. Antigens are the targets of B and T cells.
Learning and memory: adaptive immunity improves with exposure; future responses are faster and stronger upon re-encounter with the same antigen.
Not the same as neural learning; learning here refers to changes in immune cell specificity and response patterns, not neurological strengthening.
Main players:
B cells: can differentiate into antibody-producing cells; antibodies neutralize or mark pathogens for destruction.
T cells: diverse roles depending on subtype; can produce cytotoxins to kill infected cells or secrete cytokines to coordinate immune responses; some T cells function as helper cells supporting other immune cells.
CD markers and receptors:
B cells possess B cell receptors (BCR).
T cells possess T cell receptors (TCR).
CD markers (cluster of differentiation) are surface proteins used to identify and classify immune cells; two CD proteins are highlighted as important for classifying cells in this course (e.g., CD4 and CD8 are classic markers for helper and cytotoxic T cells; CD19 is a B cell marker in broader immunology discussions).
Major histocompatibility complex (MHC): critical for antigen presentation and T cell activation; two main classes:
MHC class I (MHC I)
MHC class II (MHC II)
The presence and compatibility of MHC molecules between donor and recipient is central to tissue transplantation and organ rejection; mismatch can lead to transplant failure.
B and T cell functions:
B cells: antibody production as a primary adaptive response benefit.
T cells:
Some T cells produce cytotoxins to kill compromised cells (cytotoxic T cells).
Other T cells produce signaling molecules like cytokines that coordinate immune responses.
Natural killer (NK) cells also produce cytotoxins and kill infected or abnormal cells; they are part of innate defense with cytotoxic capabilities that overlap with adaptive responses.
How adaptive responses are traced:
Antigen-specific responses are triggered when lymphocytes recognize foreign molecules via their receptors (BCRs or TCRs).
The adaptive system includes subtypes of T cells (e.g., helper, cytotoxic) and B cell subsets, with a wide array of subtypes defined by surface proteins and gene expression profiles identified using modern molecular methods.
Everyday biology connections:
Hematopoietic stem cells (HSCs) in the bone marrow give rise to all blood cells (both red and white). This includes cells involved in innate and adaptive immunity as well as erythrocytes and platelets.
Erythropoietin (EPO) drives erythropoiesis (red blood cell production), tying the hematopoietic process to oxygen transport needs.
Platelets play a key role in blood clotting and wound healing; they are not primary immune cells but are important in responses to tissue injury.
Erythrocytes (red blood cells) carry oxygen via hemoglobin; they lack a nucleus, meaning their DNA is removed during maturation, and they do not perform metabolism or repair; lifespan is finite and requires constant renewal from HSCs. Typical RBC lifespan is days.
Erythrocytes are derived from erythrocyte progenitors under regulation from EPO; platelets and other white blood cells are also regularly produced to replace aging or used cells.
Hematopoiesis and blood cell lineages (overview)
Hematopoietic stem cells (HSCs): multipotent stem cells in bone marrow that give rise to all blood lineages, including:
Red blood cells (erythrocytes) – primary function: oxygen transport via hemoglobin; life span ~ days; nucleated? no nucleus after maturation; require constant renewal.
White blood cells (leukocytes): various immune cells (neutrophils, eosinophils, basophils, monocytes, macrophages, dendritic cells, NK cells, B cells, T cells).
Platelets (thrombocytes): involved in clotting and wound repair.
Erythropoiesis: production of red blood cells driven by erythropoietin (EPO).
Monocyte–macrophage axis: monocytes in blood can exit into tissues and differentiate into macrophages; this links circulatory and tissue-resident immune defenses.
Dendritic cells: bridge innate and adaptive immunity by presenting antigens to T cells and shaping subsequent T cell responses.
Macrophages: tissue-resident phagocytes; key players in phagocytosis, antigen presentation, and inflammatory signaling.
Lymphocytes: a broad category including B cells and T cells; abundant in lymphatic tissues; the term reflects historical observation of abundant lymph in lymphatic tissue.
PMNLs (polymorphonuclear leukocytes): a term used for granulocytes with multi-lobed nuclei; three main types: neutrophils, eosinophils, basophils; recognized via morphology and staining properties, historically described by histology; modern identification often uses surface markers and gene expression.
The three main white blood cell categories can be remembered as:
Granulocytes (neutrophils, eosinophils, basophils) with granules and multi-lobed nuclei
Monocytes/macrophages (monocyte in blood; macrophage in tissue)
Lymphocytes (B cells, T cells, NK cells) with adaptive roles
“CD” (cluster of differentiation) markers: a long-term immunology effort to identify surface proteins that differentiate white blood cell subtypes; CD markers are used to classify and identify cells during functional analyses and flow cytometry. Two classic clinical examples are CD4 and CD8 on T cells, and other markers like CD19 on B cells (CD nomenclature helps define subtypes beyond morphology).
Receptor-based identification vs morphology: modern immunology uses surface protein expression (receptors and other markers) to classify cell subtypes, not solely histology, although histology historically guided naming conventions.
Antigen presentation and MHC in detail:
MHC genes encode surface proteins that present peptide antigens to T cells.
MHC I presents to CD8+ cytotoxic T cells; MHC II presents to CD4+ helper T cells; together they enable recognition of intracellular and extracellular pathogens by T cells.
Tissue compatibility for organ transplants depends on matching MHC molecules; mismatches can trigger organ rejection and are a major clinical concern in transplantation.
The lecture teases deeper exploration of MHC biology in tomorrow’s session, indicating the complexity and significance of MHC in immunity and transplantation.
Quick glossary of key terms (from lecture context)
Antigen: a foreign molecule that triggers an immune response; in practice, the molecules on pathogens that the immune system recognizes.
Antibody: produced by B cells; mediates pathogen neutralization and clearance.
B cell receptor (BCR): membrane-bound immunoglobulin on B cells that recognizes specific antigens.
T cell receptor (TCR): antigen-specific receptor on T cells recognizing peptide-MHC complexes.
Erythrocyte (RBC): red blood cell; transports oxygen; lacks a nucleus and has a lifespan of days in humans.
Hematopoietic stem cell (HSC): stem cell in bone marrow that gives rise to all blood cells.
Erythropoietin (EPO): hormone that stimulates erythropoiesis (RBC production).
Defensins: antimicrobial peptides targeting bacteria.
Interferon: antiviral cytokine that helps limit viral replication.
Complement: a group of blood proteins that participate in microbial killing; relies on presence of infection in the bloodstream to exert full effect.
MHC I / MHC II: major histocompatibility complex classes I and II; present antigens to CD8+ and CD4+ T cells, respectively; critical for immune recognition and transplantation compatibility.
PMNL: polymorphonuclear leukocytes; a label used for granulocytes with multi-lobed nuclei (neutrophils, eosinophils, basophils).
Lymphocyte: white blood cell type enriched in lymphatic tissue; includes B cells, T cells, and NK cells.
Pluripotent / totipotent: terms describing the potential to differentiate into multiple or all cell types; pluripotent denotes a wide but not all-encompassing developmental potential; totipotent denotes the potential to differentiate into all cell types including extraembryonic tissues.
Hematopoiesis: the process of blood cell formation from hematopoietic stem cells.
Practical and real-world connections
Regenerative medicine and stem cells:
Induced pluripotent stem cells (iPSCs) can reprogram differentiated cells to an embryonic-like state, allowing controlled differentiation into various tissue types for therapeutic purposes.
Efforts to generate specific tissue types (e.g., myocardium, nervous tissue) face challenges in recapitulating native tissue architecture and function; ongoing research aims to guide stem cells with precise signals to become desired tissue types.
Clinical relevance of stem cell biology:
Hematopoietic stem cells are central to lifelong production of blood cells; therapies often rely on manipulating these cells (e.g., bone marrow transplants).
Erythropoietin is clinically used to stimulate RBC production in certain anemias; misuse in sports (doping) is discussed as a cautionary note.
Transplantation and immunology:
MHC matching is crucial for minimizing transplant rejection; understanding MHC diversity explains why individuals respond differently to organ grafts.
The lecture hints at the complexity of the immune system’s memory and learning mechanisms, which underlie vaccine design and long-term immunity strategies.
Ethical and practical implications:
Stem cell therapies raise ethical questions about sourcing, consent, and long-term impacts.
The balance between advancing regenerative medicine and ensuring patient safety is a core theme in translational immunology and biotechnology.
Quick study tips (from the lecture approach)
Use the three-layer defense model to organize study notes: Barriers → Innate → Adaptive.
Memorize key cell types and their primary roles (neutrophils, macrophages, dendritic cells, NK cells; B and T cells).
Connect cell types to their functions: e.g., NK cells kill compromised cells; neutrophils perform rapid phagocytosis; dendritic cells present antigens to adaptive partners.
Recall the meaning of common prefixes (erythro-, leuko-, cyto-, PMNL) to quickly deduce cell types and tissues.
Understand MHC and CD markers as essential tools for identifying and matching immune cells and tissues in research and clinical settings.
Remember RBC lifespans and production dynamics to grasp daily hematopoietic demands (e.g., RBC turnover vs. WBC turnover).
Be aware of how the immune system’s memory arises (adaptive learning) and why this matters for vaccines and repeated exposures.
Summary takeaways
The immune system operates in layered defenses: physical barriers, innate rapid responders, and adaptive, learning responders.
The innate layer provides immediate defense and shapes the adaptive response, using cells like neutrophils, macrophages, dendritic cells, and NK cells, plus molecules like defensins, interferons, cytokines, and complement.
The adaptive layer (B and T cells) learns from pathogens, creates antibodies and cytotoxic/cytokine responses, and generates immunological memory for faster future responses.
Blood cell formation (hematopoiesis) in the bone marrow continuously renews erythrocytes, leukocytes, and platelets; RBCs have a defined lifespan and unique structural features (no nucleus).
MHC molecules and CD markers are central to antigen presentation, cell identification, and transplant compatibility, with broad clinical relevance in infection defense and organ transplantation.
The field integrates biology with technology (molecular markers, iPSCs, transplantation science) and raises important ethical and practical considerations for medicine and research.