43 Chapter Flashcards
Pathogen
A bacterium, fungus, virus, or other disease-causing agent
Immune system function
Enables an animal to avoid or limit many infections
Two types of immune defense found among animals:
Innate immunity (all animals)
Adaptive immunity (only vertebrates)
Innate immunity
Includes barrier defenses and molecular recognition which enables responses to a broad range of pathogens
Adaptive immunity (adaptive/acquired immune response)
Molecular recognition with tremendous specificity
Lysozyme
An enzyme that breaks down bacterial cell walls
Antimicrobial peptides
Short chains of amino acids secreted by hemocytes to combat pathogens in innate immunity
Hemocytes
Immune cells of insects
Innate defenses similar between invertebrates and vertebrates
Barrier defense, phagocytosis, and antimicrobial peptides
Innate defenses unique to vertebrates
Natural killer cells, interferons, and the inflammatory response
Mucus
A viscous fluid that traps pathogens and other particles
Toll-like receptor (TLR)
A membrane receptor on a phagocytic white blood cell that recognizes fragments of molecules common to a set of pathogens
The two main types of phagocytic cells in the mammalian body:
Neutrophils and macrophages
Neutrophil
The most abundant type of white blood cell. Neutrophils are phagocytic and tend to self-destruct as they destroy foreign invaders, limiting their life span to a few days.
Macrophage
A phagocytic cell present in many tissues that functions in innate immunity by destroying microbes and in acquired immunity as an antigen-presenting cell
Dendritic cells
Mainly populate tissues, such as skin, that contact the environment. Is an antigen-presenting cell that is particularly efficient in presenting antigens to helper T cells, thereby initiating a primary immune response.
Eosinophils
Often found beneath mucosal surfaces, are important in defending against multicellular invaders, such as parasitic worms.
Natural killer cells
Circulate through the body and detect the abnormal array of surface proteins characteristic of some virus-infected and cancerous cells
Interferon
A protein that has antiviral or immune regulatory functions. Interferon-α and interferon-β, secreted by virus infected cells, help nearby cells resist viral infection; interferon-ν, secreted by helper T cells, helps activate macrophages
Complement system
A group of about 30 proteins that may amplify the inflammatory response, enhance phagocytosis, or directly lyse (burst) extracellular pathogens
Inflammatory response
The changes brought about by signaling molecules released upon injury or infection
Histamine
An important inflammatory signaling molecule, which is stored in densely packed vesicles of mast cells. Histamine triggers nearby blood vessels to dilate and become more permeable.
Mast cells
A vertebrate body cell that produces histamine and other molecules that trigger inflammation in response to infection and in allergic reactions
Cytokines
Signaling molecules that modulate immune responses
Pus
A fluid rich in white blood cells, dead pathogens, and cell debris from damaged tissue
The adaptive response relies on T cells and B cells, which are types of white blood cells called ____________
Lymphocytes
Like all blood cells, lymphocytes originate from ____________
Stem cells in the bone marrow
Thymus
An organ in the thoracic cavity above the heart
How are T cells made?
From lymphocytes that migrate and develop in the thymus
How are B cells made?
From lymphocytes that develop in the bone marrow
T cells
The class of lymphocytes that mature in the thymus; they include both effector cells for the cell-mediated immune response and helper T cells required for both branches of adaptive immunity
B cells
The lymphocytes that complete their development in the bone marrow and become effector cells for the humoral immune response
Antigen
Any substance that elicits a B or T cell response
Antigen receptor
A protein which binds a B or T cell to an antigen
Epitope
The small, accessible portion of an antigen that binds to an antigen receptor
B cell antigen receptor structure
A Y-shaped molecule consisting of four polypeptide chains: two identical heavy chains and two identical light chains, with disulfide bridges linking the chains together
Heavy chain
One of the two types of polypeptide chains that make up an antibody molecule and B cell receptor; consists of a variable region, which contributes to the antigen-binding site, and a constant region
Light chain
One of the two types of polypeptide chains that make up an antibody molecule and B cell receptor; consists of a variable region, which contributes to the antigen-binding site, and a constant region
Constant (C) region
Includes the cytoplasmic tail and transmembrane region of the heavy chain and all of the disulfide bridges
Variable (V) region
Component of the heavy and light chains of a B cell antigen receptor. So named because it’s amino acid sequence varies extensively from one B cell to another.
Together, pars of a heavy-chain V region and a light-chain V region form an asymmetric binding site for an antigen
True
Antibody/ Immunoglobulin (Ig)
The soluble form of the B cell antigen receptor
It is antibodies, rather than B cells themselves, that actually help defend against pathogens
True
T cell antigen receptor structure
Two different polypeptide chains, an α chain and a β chain, linked by a disulfide bridge
At the outer tip of the T cell receptor, the variable (V) regions of the α and β chains together form a single antigen-binding site. The remainder of the molecule is made up of the constant (C) regions.
True
Difference in B and T cell receptor binding
B cell (antigen) receptors bind to epitopes of intact antigens on pathogens, whereas T cell receptors bind only to fragments of antigens that are displayed, or presented, on the surface of host cells.
Major histocompatibility complex (MHC) molecule
The host protein that displays the antigen fragments on the cell surface
Antigen fragments
Peptides of the antigen
Antigen presentation
The process by which an MHC molecule binds to a fragment of an intracellular protein antigen and carries it to the cell surface, where it is displayed and can be recognized by a T cell
Self-tolerance
The lack of reactivity against an animal’s own molecules and cells.
A receptor light chain is encoded by three gene segments:
A variable (V) segment, a joining (J) segment, and a constant (C) segment. The V and J segments together encode the variable region of the receptor chain, while the C segment encodes the constant region
Effector cells
Short-lived cells that take effect immediately against the antigen and any pathogens producing that antigen.
Are developed from T or B cell proliferation
Plasma cells
The effector forms of B cells, which secrete antibodies.
Effector forms of T cells:
Helper T cells and cytotoxic T cells
Memory cells
Result from B and T cell proliferation. Are long-lived cells that can give rise to effector cells if the same antigen is encountered later in the animal’s life
Clonal selection
The process by which an antigen selectively binds to and activates only those lymphocytes bearing receptors specific for the antigen. The selected lymphocytes proliferate and differentiate into a clone of effector cells and a clone of memory cells specific for the stimulating antigen.
Primary immune response
The initial adaptive immune response to an antigen, which appears after a lag of about 10-17 days
Secondary immune response
The adaptive immune response elicited on second or subsequent exposures to a particular antigen. The secondary immune response is more rapid, of greater magnitude, and of longer duration than the primary immune response
The humoral immune response occurs in _______________
The blood and lymph
In the humoral immune response…
Antibodies help neutralize or eliminate toxins and pathogens in the blood and lymph
In the cell-mediated immune response, ___________________
Specialized T cells destroy infected host cells
Helper T cell
A type of T cell that, when activated, secretes cytokines that promote the response of B cells (humoral response) and cytotoxic cells (cell-mediated response) to antigens.
Antigen-presenting cell
A cell that upon ingesting pathogens or internalizing pathogen proteins generates peptide fragments that are bound by class II MHC molecules and subsequently displayed on the cell surface to T cells. Macrophages, dendritic cells, and B cells are the primary antigen-presenting cells
Cytotoxic T cells
A type of lymphocyte that, when activated, kills infected cells as well as certain cancer cells and transplanted cells. Uses toxic proteins to kill cells infected by viruses or other intracellular pathogens before pathogens fully mature.
Neutralization
A process in which antibodies bind to proteins on the surface of a virus
Opsonization
A process in which antibodies bind to antigens on bacteria but do not block infection, instead present a readily recognized structure for macrophages or neutrophils, thereby promoting phagocytosis
Active immunity
The defenses that arise when a pathogen infects the body and prompts a primary or secondary immune response
Passive immunity
When the antibodies in the recipient are produced by another individual. For example pregnancy
Immunization
The process of generating a state of immunity by artificial means.
Vaccination
A type of artificial active immunization where an inactive or weakened form of a pathogen is administered, inducing B and T cell responses and immunological memory.
Passive immunization
Antibodies specific for a particular pathogen are administered, conferring immediate but temporary protection
Monoclonal antibodies
Any of a preparation of antibodies that have been produced by a single clone of cultured cells and thus are all specific for the same epitope
Allergies
Are exaggerated (hypersensitive) responses to certain antigens called allergens
Autoimmune disease
An immunological disorder in which the immune system turns against self
Immunodeficiency
A disorder in which an immune system response to antigens is defective or absent
Inborn immunodeficiency
Results from a genetic or developmental defect in the production of immune system cells or of specific proteins, such as antibodies or the proteins of the complement system
Acquired immunodeficiency
Caused by exposure to certain chemicals or biological agents
Antigenic variation
Pathogenic changes in epitope which thwart immunological memory
Latency
An inactive state of a virus after infecting cells. Latent viruses do not trigger adaptive immune response
Human immunodeficiency virus (HIV)
The pathogen that causes AIDS, both escapes and attacks the adaptive immune response
Acquired immunodeficiency syndrome
An impairment in immune responses that leaves the body susceptible to infections and cancers that a healthy immune system would usually defeat
