Immune System Flashcards

Flashcards about the Immune System and the Body's Defense

Immune System

Protects us from infectious agents & harmful substances. Composed of numerous cellular & molecular structures that function together to provide immunity. Function dependent on the specific type of infectious agent.

Bacteria

Spherical (cocci), rodlike (bacilli), or coiled (spirilla). Most are harmless; some virulent (cause serious illness).

Viruses

Pieces of DNA or RNA in a protein shell. They are not cells and are much smaller. Obligate intracellular parasites. E.g., common cold, ebola, chickenpox

Fungi

Eukaryotic cells with membrane & cell wall. Include molds, yeasts, multicellular fungi that produce spores. Cause superficial diseases (e.g., ringworm), infect mucosal linings, or cause internal infections (e.g., histoplasmosis)

Protozoans

Eukaryotic cells without a cell wall. Intracellular & extracellular parasites. Disease examples: malaria & trichomoniasis

Multicellular Parasites

Nonmicroscopic, take nourishment from the host they live in. E.g., tapeworm

Prions

Fragments of infectious proteins that cause disease in nervous tissue. E.g., Variant Creutzfeldt-Jakob disease

Leukocytes

Formed in red bone marrow. Include granulocytes (neutrophils, eosinophils, basophils), monocytes (become macrophages), and lymphocytes (B-lymphocytes, T-lymphocytes, NK cells)

Cytokines

Small proteins that regulate immune activity. Act on the cell that released it (autocrine), on local cells (paracrine), or on distant cells (endocrine). Effects include signaling cells, controlling the development & behavior of immune cells, regulating the inflammatory response, and destroying cells

Innate Immunity

Present at birth. Protects against a variety of different substances (nonspecific). Includes barriers of skin & mucosal membranes, nonspecific cellular & molecular internal defenses. Responds immediately to potentially harmful agents

Adaptive Immunity

Acquired immunity. Response to antigen involves specific T- & B-lymphocytes. Takes several days to be effective

Neutrophils, Macrophages, & Dendritic Cells

Cells of innate immunity that engulf unwanted substances by phagocytosis. Destroy engulfed particles & then present fragments (antigens) on their surface to T-lymphocytes

Basophils & Mast Cells

Promote inflammation by releasing granules containing chemicals. Histamine increases vasodilation & capillary permeability. Heparin acts as an anticoagulant. Eicosanoids released from their plasma membrane also increase inflammation

Natural Killer Cells

Destroy virus-infected cells, bacteria-infected cells, tumor cells, cells of transplanted tissue. Kill by releasing cytotoxic chemicals: Perforin creates a transmembrane pore, and granzymes enter the pore & cause apoptosis of the cell

Eosinophils

Attack multicellular parasites. Degranulate, release enzymes & toxic substances. Participate in immune responses of allergy & asthma. Engage in phagocytosis of antigen-antibody complexes

Antimicrobial Proteins

Molecules that function against microbes. Interfere with viral spread. IFN-g produced by T-lymphocytes & NK cells stimulates macrophages. IFN-a & IFN-b produced by leukocytes & virus-infected cells prevent their infection

Complement System

Group of over 30 plasma proteins that work along with antibodies. Activation occurs by enzyme cascade. Activation follows pathogen entry. Complement protein (opsonin) binds to pathogen enhancing phagocytosis of pathogenic cell

Inflammation

Immediate response to ward off unwanted substances. Local, nonspecific response of vascularized tissue to injury. Events include vascular changes, recruitment of leukocytes, and release of chemicals

Fever

Abnormal body temperature elevation, Results from the release of pyrogens from immune cells or infectious agents, Inhibits reproduction of bacteria & viruses, promotes interferon activity, increases activity of adaptive immunity, and accelerates tissue repair

Pus

Exudate containing destroyed pathogens, dead leukocytes, macrophages, & cellular debris. Removed by lymphatic system or through skin; if not completely cleared, may form abscess

Chronic Inflammation

Inflammation continuing for longer than two weeks. Characterized by macrophages & lymphocytes (not neutrophils). Can occur from overuse injuries or autoimmune disorder. Can lead to tissue destruction & scar tissue formation

Antigen

Substance that binds a T-lymphocyte or antibody. Usually a protein or large polysaccharide (capsid of viruses, cell wall of bacteria or fungi, bacterial toxins, abnormal proteins or tumor antigens)

Antigenic Determinant (Epitope)

Specific site on antigen recognized by the immune system

Immunogen

Antigen that induces an immune response. Immunogenicity increases with antigen’s degree of foreignness, size, complexity, or quantity

Haptens

Small foreign molecules that induce immune response when attached to a carrier molecule in host. E.g., toxin in poison ivy. Account for hypersensitivity reactions

Autoimmune Disorder

Immune system lacking tolerance for specific self-antigen. Initiates immune response as if cells were foreign. E.g., rheumatic heart disease, type 1 diabetes, multiple sclerosis

TCR (T-cell receptor)

Antigen receptor of T-lymphocyte

BCR (B-cell receptor)

Antigen receptor of B-lymphocyte

Helper T-lymphocytes

CD4+ cells that assist in cell-mediated, humoral, & innate immunity. E.g., activate NK cells & macrophages

Cytotoxic T-lymphocytes

CD8+ cells that release chemicals that destroy other cells

Antigen Presentation

Cells display antigen on plasma membrane so T-cells can recognize it

Major Histocompatibility Complex (MHC)

Group of transmembrane proteins. MHC I is found on all nucleated cells; MHC II is found on APCs

Formation & Maturation of Lymphocytes

Occurs in primary lymphatic structures (red marrow & thymus). Lymphocytes become able to recognize one specific foreign antigen

Activation of Lymphocytes

In secondary lymphatic structures lymphocytes are exposed to antigen & become activated, replicating to form identical lymphocytes

Effector Response

Action of lymphocytes to eliminate antigen. T-lymphocytes migrate to site of infection; B-lymphocytes stay in secondary lymphatic structure (as plasma cells)

Positive Selection - Thymic

Ability of T-cells to bind thymic epithelial cells with MHC molecules

Negative Selection - Thymic

Ability of T-lymphocyte to NOT bind self-antigens (self-tolerance)

Clonal Selection

Forming clones in response to an antigen; all formed cells have same TCR or BCR that matches specific antigen

Antigen Challenge

First encounter between antigen & lymphocyte (usually in secondary lymphatic structures)

Lymphocyte Recirculation

After several days, a lymphocyte exits secondary lymphatic structure and circulates through blood & lymph

Antibodies

Immunoglobulin proteins produced against a particular antigen. Soluble antigens are combatted by humoral immunity

Neutralization

Antibody physically covers antigenic determinant of pathogen, making it ineffective in establishing infection

Agglutination

Antibody cross-links antigens of foreign cells causing clumping, effective against bacterial cells

Precipitation

Antibody cross-links circulating antigens forming antigen-antibody complex that becomes insoluble & precipitates out of body fluids

Complement Fixation

Fc region of IgG & IgM can bind complement for activation

Opsonization - Antibodies

Fc region of certain antibody classes makes it more likely target cell will be “seen” by phagocytic cells

Activation of NK cells

Antibody (IgG) triggers NK cells to release cytotoxins which destroys abnormal cells

Antibody Titer

A measure of immunologic memory

Active Immunity

Results from direct encounter with pathogen (naturally or artificially through vaccine). Memory cells against specific antigen are formed

Passive Immunity

Obtained from another individual (transfer of antibodies from mother to fetus or serum containing antibodies transferred from one person to another)

Vaccination

Weakened or dead microorganism or component which stimulates immune system to develop memory B-lymphocytes

Hypersensitivity

Abnormal & exaggerated response of immune system to antigen

Allergy

Overreaction of immune system to a noninfectious substance (allergen). May cause multiple symptoms & potentially anaphylactic shock

AIDS

Life-threatening condition resulting from HIV, which infects & destroys helper T-lymphocytes