Chapter 22: The Immune System Vocabulary

Vocabulary flashcards covering key terms, cell types, cytokines, immunoglobulins, and mechanisms of innate and adaptive immunity based on Chapter 22 notes.

Infectious Agents

Organisms that invade a host organism and cause damage or possibly death. (Slide 3)

Pathogenic

A term describing an infectious agent that causes harm or disease to a host. (Slide 3)

Five Major Classes of Infectious Agents

Bacteria, viruses, fungi, protozoans, and parasites. (Slide 3)

Bacteria

A major class of single-celled prokaryotic infectious agents capable of causing disease in a host. (Slide 3)

Viruses

A major class of microscopic non-cellular infectious agents that require host cells to replicate. (Slide 3)

Fungi

A major class of eukaryotic infectious agents, such as yeasts and molds, capable of causing disease in a host. (Slide 3)

Protozoans

A major class of microscopic, single-celled eukaryotic infectious agents that can infect host tissues. (Slide 3)

Parasites

A major class of infectious organisms that live on or inside a host organism and derive nutrients at the host's expense. (Slide 3)

Immunity

The body's ability to protect itself against potentially harmful substances. (Slide 5)

Five Immune Cells in Secondary Lymphoid Structures

T-lymphocytes, B-lymphocytes, Natural Killer (NK) cells, macrophages, and dendritic cells. (Slide 5, 19)

Leukocytes (WBCs)

Specialized white blood cells formed in red bone marrow via leukopoiesis that serve as the primary cells of the immune system. (Slide 6)

Three Types of Granulocytes

Neutrophils, eosinophils, and basophils. (Slide 6)

Cells Formed from Monocytes Exiting Blood

Macrophages and dendritic cells. (Slide 6)

Three Types of Lymphocytes

T-cells, B-cells, and Natural Killer (NK) cells. (Slide 6)

Mast Cells

Proinflammatory cells located in connective tissue (dermis, respiratory, GI, and genitourinary tracts) near small blood vessels that function similarly to basophils. (Slide 6)

Dermis Location of Mast Cells

Mast cells are situated in the connective tissue of the skin's dermis, close to small blood vessels. (Slide 6)

Respiratory Tract Locations of Mast Cells

Nose, trachea, bronchi, and lungs within mucosal connective tissue. (Slide 6)

Digestive and Excretory System Locations of Mast Cells

Gastrointestinal tract (GIT) and genitourinary tract. (Slide 6)

Comparison Between Mast Cells and Basophils

Mast cells function similarly to basophils but are located in connective tissue near blood vessels rather than circulating in the blood. (Slide 6)

Stem Cell Branches in Leukopoiesis

Blood stem cells divide into myeloid stem cells (giving rise to RBCs, platelets, and myeloblasts) and lymphoid stem cells (giving rise to lymphoblasts). (Slide 7)

Granulocyte Sequence of Development

Myeloid stem cell -> Myeloblast -> Granulocytes (Eosinophil, Basophil, Neutrophil). (Slide 7)

Lymphocyte Sequence of Development

Lymphoid stem cell -> Lymphoblast -> Lymphocytes (B lymphocyte, T lymphocyte, Natural Killer cell). (Slide 7)

Cytokines

Small, soluble proteins produced and released by cells to regulate immune activity, control cell behavior, regulate inflammation, and destroy cells. (Slide 8)

Interleukin (IL)

A category of cytokines produced by T-lymphocytes, macrophages, and endothelial cells that primarily regulates immune cells. (Slide 9)

Tumor Necrosis Factor (TNF)

A category of cytokines produced by T-lymphocytes, macrophages, mast cells, and dendritic cells that destroys tumor cells. (Slide 9)

Colony-Stimulating Factor (CSF)

A category of cytokines that stimulates leukopoiesis in bone marrow to increase the synthesis of specific leukocyte types. (Slide 9)

Interferon (IFN)

A category of cytokines produced by infected cells, NK cells, and T-lymphocytes that interferes with the replication of intracellular pathogens. (Slide 9)

Innate Immunity

Nonspecific immune structures, substances, or processes present from birth that provide immediate defense against a variety of pathogens. (Slide 11)

Two Lines of Defense of Innate Immunity

1st Line is preventing entry of pathogens into the body, and 2nd Line is activating the nonspecific internal defenses. (Slide 11)

Physical Barriers of Innate Immunity

Skin (keratinized stratified squamous epithelium, areolar and dense irregular CT) and mucous membranes of the respiratory, GI, urinary, and reproductive tracts. (Slide 12)

Chemical Barriers of Innate Immunity

Hyaluronic acid, exocrine secretions (sweat lysozymes, oil gland lactate/fatty acids), saliva (lysozymes and IgA), low stomach pH, and mucin/mucus (containing defensins, lysozymes, and IgA). (Slide 13)

Hyaluronic Acid

A gel-like substance in the areolar connective tissue of the skin that slows microbe migration. (Slide 13)

Mucin

A protein in mucous membranes that becomes mucus when hydrated, containing antimicrobial substances such as lysozymes, defensins, and IgA. (Slide 13)

Physiologic Mechanisms of First-Line Defense

Cilia mucus elevator, coughing, sneezing, defecation, vomiting, urinary flushing, vaginal acidic secretions, and commensal microbiota. (Slide 14)

Commensal Microbiota (Human Microbiome)

Nonpathogenic microorganisms living throughout the human body that prevent colonization by harmful pathogens as part of the first-line defense. (Slide 14)

Four Components of Nonspecific Internal Defenses

1. Immune cells (except T- and B-cells), 2. Antimicrobial proteins, 3. Inflammation, and 4. Fever; initiated when 1st line defenses are ineffective. (Slide 16)

Toll-like Receptors (TLRs)

Pattern recognition receptors on immune cells that detect common molecular structures on the surface of foreign microbes. (Slide 16)

Phagocytic Cells of Innate Immunity

Neutrophils (targeting bacteria), macrophages, and dendritic cells (found in skin and mucous membranes). (Slide 17)

Proinflammatory Chemical-Secreting Cells

Basophils (circulating in blood) and mast cells (in connective tissues) that secrete chemicals to increase fluid movement and recruit immune cells. (Slide 18)

Chemotaxic Chemicals

Substances released by cells such as basophils and mast cells that attract other immune cells to the site of injury or infection. (Slide 18)

Natural Killer (NK) Cells

Lymphocytes involved in innate immune surveillance that destroy unhealthy or virus-infected cells via apoptosis using perforin and granzymes. (Slide 19)

Perforin and Granzymes

Cytotoxic chemicals released by Natural Killer (NK) cells; perforin forms transmembrane pores in target cell membranes, and granzymes enter to induce apoptosis. (Slide 19)

Eosinophils

Leukocytes that target parasites by releasing pore-forming proteins against their surface, also active in allergies and asthma. (Slide 20)

Antimicrobial Proteins: Interferons

A category of cytokines that interfere with the process of pathogen replication within host cells as part of the second line of defense. (Slide 21)

Action of Interferons Against Viral Infection

Interferons do not directly kill viruses; instead, they are released by infected cells to signal neighboring uninfected cells to become resistant and activate immune cells. (Slide 22, 23)

Steps 1-4 of Interferon Early Signaling Cascade

1. Virus infects a body cell and hijacks its machinery. 2. Infected cell detects viral genetic material and synthesizes interferons ($\text{IFN}-\alpha$, $\text{IFN}-\beta$). 3. Infected cell secretes interferons into surrounding tissue. 4. Interferons bind to receptors on neighboring healthy cells, triggering protective gene expression to resist infection. (Slide 23)

Steps 5-6 of Interferon Signaling Cascade

5. Healthy cells produce antiviral proteins (PKR, RNase L, Mx proteins) to destroy viral RNA and block viral replication. 6. Interferons activate Natural Killer (NK) cells to release perforin and granzymes, inducing apoptosis in infected cells. (Slide 24)

Step 7 of Interferon Signaling Cascade

7. Interferons increase macrophage activity, making them more effective at phagocytosis, killing pathogens, and presenting antigens to T-cells. (Slide 25)

Interferon-Alpha (IFN-\alpha)

An interferon produced by virus-infected leukocytes (especially plasmacytoid dendritic cells) that provides strong antiviral defense and activates NK cells. (Slide 25)

Interferon-Beta (IFN-\beta)

An interferon produced by virus-infected fibroblasts and other cells that protects nearby uninfected cells from viral infection. (Slide 25)

Interferon-Gamma (IFN-\gamma)

An interferon produced by T-lymphocytes and NK cells that activates macrophages and strengthens adaptive immunity. (Slide 25)

Complement System

A group of liver-produced plasma proteins circulating in inactive forms that complement antibodies during innate immune responses via classical, alternative, or lectin pathways. (Slide 26)

Opsonization (Complement Defense)

A mechanism of complement defense where complement proteins (such as $\text{C3b}$) binding to a pathogen act as a red flag (opsonin) to enhance phagocytosis by leukocytes. (Slide 26)

Elimination of Immune Complexes

A complement mechanism where complement proteins link antigen-antibody complexes to erythrocytes, which carry them to the liver and spleen for macrophage clearance. (Slide 26)

Cytolysis (Membrane Attack Complex)

A complement mechanism where complement components ($\text{C5b}-\text{C9}$) form a Membrane Attack Complex (MAC) that creates pores in a target cell membrane, causing cell lysis. (Slide 26)

General Characteristics of Inflammation

An immediate, localized event occurring in vascularized tissue in response to injury-causing stimuli that helps eliminate most infectious agents and unwanted substances. (Slide 27)

Four Main Events of Inflammation

1. Release of proinflammatory chemicals. 2. Local vascular changes. 3. Recruitment of leukocytes. 4. Delivery of plasma proteins (immunoglobulins, complement, clotting proteins, kinins). (Slide 27)

Detailed Steps 1-4 of Inflammatory Response

1. Damaged cells release proinflammatory chemicals (histamine, prostaglandins, etc.). 2. Released chemicals cause local blood vessels to respond and express cell-adhesion molecules (CAMs). 3. Leukocytes are recruited to the site of injury. 4. Plasma proteins (immunoglobulins, complement proteins, clotting proteins, and kinins) are delivered to the injury site. (Slide 28)

Cell-Adhesion Molecules (CAMs)

Surface proteins expressed on endothelial cells of local blood vessels during inflammation that assist in leukocyte recruitment. (Slide 28)

Rubor (Redness)

The cardinal sign of inflammation representing redness caused by vasodilation and increased blood flow to the injured area. (Slide 29)

Calor (Heat)

The cardinal sign of inflammation representing localized heat resulting from increased blood flow and metabolic activity. (Slide 29)

Tumor (Swelling)

The cardinal sign of inflammation representing swelling caused by increased fluid movement from capillaries into the interstitial space. (Slide 29)

Dolor (Pain)

The cardinal sign of inflammation representing pain due to receptor compression and chemical irritation by kinins and prostaglandins. (Slide 29)

Functio Laesa

The cardinal sign of inflammation representing loss of function, protecting the affected area from further damage. (Slide 29)

Pyrexia

An abnormal elevation of core body temperature of at least $1\,^{\circ}\text{C}$ ($1.8\,^{\circ}\text{F}$) above the standard $37\,^{\circ}\text{C}$ ($98.6\,^{\circ}\text{F}$). (Slide 31)

Pyrogens

Fever-inducing molecules released by infectious agents or immune cells that target the hypothalamus to raise the body's temperature set point. (Slide 31)

Fever Stage: Onset

The initial stage of fever initiated when pyrogens target the hypothalamus to raise the set point above $37\,^{\circ}\text{C}$, leading to dermal vasoconstriction and shivering to increase heat production. (Slide 31)

Fever Stage: Stadium

The period during which the elevated core body temperature is maintained, increasing metabolic rates to help the immune system eliminate harmful substances. (Slide 31)

Fever Stage: Defervescence

The stage when the fever breaks as pyrogen stimulation ceases, resetting the hypothalamus back to normal core temperature and dissipating heat through vasodilation and sweating. (Slide 31)

Adaptive Immunity

The third line of defense involving T-cells and B-cells that produces a specific, long-term immune response following exposure to an antigen. (Slide 33)

Two Branches of Adaptive Immunity

Cell-mediated immunity (carried out by T-cells) and antibody-mediated / humoral immunity (carried out by B-cells). (Slide 34)

Helper T-Cells (Cell-Mediated Immunity)

Differentiated T-lymphocytes formed during cell-mediated immunity that coordinate overall immune responses. (Slide 34)

Cytotoxic T-Cells (Cell-Mediated Immunity)

Differentiated T-lymphocytes formed during cell-mediated immunity that release toxic chemicals to destroy unhealthy or infected host cells. (Slide 34)

Plasma Cells

Differentiated B-lymphocytes that synthesize and release antibodies to bind and neutralize extracellular pathogens. (Slide 34)

Antigen

A unique molecule (typically a protein or large polysaccharide) capable of binding to components of the adaptive immune system. (Slide 35)

Self-Antigens vs. Foreign Antigens

Self-antigens are molecules belonging to body cells, whereas foreign (nonself) antigens originate from infectious agents or non-body sources. (Slide 35)

Autoimmune Disorders

Conditions caused when lymphocytes react against self-antigens due to an inability to distinguish self-antigens from foreign antigens. (Slide 35)

Epitope (Antigenic Determinant)

The specific site on an antigen where a lymphocyte receptor or antibody physically binds. (Slide 36)

Immunogenicity

The ability of an antigen to induce an immune response, which increases with larger molecular size. (Slide 37)

TCR and BCR

Antigen receptor complexes located on lymphocyte cell surfaces: T-cell receptors (TCRs) on T-cells and B-cell receptors (BCRs) on B-cells. (Slide 38)

Difference in Antigen Contact Between B-Cells and T-Cells

B-cells can directly contact antigens without assistance, whereas T-cells require antigens to be presented by an antigen-presenting cell (APC). (Slide 38)

T-Cell Coreceptors (CD Molecules)

Molecules on T-cell surfaces (such as $\text{CD}4$ and $\text{CD}8$) that assist T-cell receptors in recognizing antigens presented by antigen-presenting cells. (Slide 39)

Helper T-Cells (T_H)

T-lymphocytes bearing $\text{CD}4$ coreceptors that coordinate overall immune responses and activate NK cells and other leukocytes. (Slide 40)

Cytotoxic T-Cells (T_C)

T-lymphocytes bearing $\text{CD}8$ coreceptors that destroy unhealthy or infected host cells by releasing toxic chemicals. (Slide 40)

Antigen Presentation

The process of displaying processed antigens on MHC molecules on cell surfaces for recognition by helper T-cells and cytotoxic T-cells. (Slide 41)

Antigen-Presenting Cells (APCs)

Specialized cells including macrophages, dendritic cells, and B-cells that present processed antigens on their surface to T-cells. (Slide 41)

Major Histocompatibility Complex (MHC)

The specific physical site on an antigen-presenting cell where a processed antigen attaches to be presented to a T-cell. (Slide 41)

MHC Class I Molecules

MHC molecules present on all nucleated cells used primarily to present endogenous antigens to $\text{CD}8^+$ Cytotoxic T-cells. (Slide 41)

MHC Class II Molecules

MHC molecules found on professional APCs used primarily to present exogenous antigens to $\text{CD}4^+$ Helper T-cells. (Slide 41)

IgG Class Antibody

The immunoglobulin present in the greatest abundance in the blood. (Slide 44)

IgA Class Antibody

The immunoglobulin found predominantly around body openings in secretions such as saliva, tears, and breast milk. (Slide 44)

IgM Class Antibody

The immunoglobulin produced first during a primary infection. (Slide 44)

IgE Class Antibody

The immunoglobulin associated with allergic reactions and defense against parasitic infections. (Slide 44)

IgD Class Antibody

The immunoglobulin that functions in the development and activation of B-cells. (Slide 44)

IgD Class Antibody

The immunoglobulin that functions in the development and activation of B-cells. (Slide 44)

Immunoglobulin (Antibody)

Specialized Y-shaped proteins synthesized and released by plasma cells (differentiated B-lymphocytes) that specifically bind to extracellular antigens to neutralize or facilitate the destruction of pathogens. (Slide 34, 44)