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pathogen
foreign agent that causes diseases
immune system
animal body’s system of defenses against agents that cause disease
innate immunity
form of defense in all animals that’s active immediately upon exposure to pathogens and is the same whether or not the pathogen has been previously encountered, includes barrier and internal defenses, provides a generic response from a small set of receptors
adaptive immunity
vertebrate-specific defense that develops following exposure to pathogens, mediated by B & T lymphocytes, includes humoral & cell-mediated responses, provides a specific response
phagocytosis
ingestion and breakdown of foreign substances
exoskeleton
physical barrier against infection
lysozyme
enzyme that destroys bacterial cell walls in the digestive tract; found in sweat, tears, and saliva
hemocytes
immune cells of insects that produce proteins that bind to molecules specific to a broad class of pathogens, carry out phagocytosis and release antimicrobial proteins
characteristics of innate immunity of all animals
barrier defenses, phagocytosis, antimicrobial proteins
characteristics of innate immunity unique to vertebrates
natural killer cells, interferons, inflammatory response
Where can a mucous membrane be found?
urinary, respiratory, reproductive, and digestive systems
mucus
viscous fluid produced by the mucous membrane that traps pathogens and other particles
components of the body hostile to many pathogens
saliva, mucus, tears because of lysozymes and skin and digestive system because of low pH
What do phagocytic cells recognize and how?
recognize viral, fungal, and bacterial components by Toll-like receptors (TLRS)
Toll-like receptor (TLR)
membrane receptor on a phagocytic WBC that recognizes fragments of molecules common to a set of pathogens
main types of phagocytic cells
neutrophils and macrophages
neutrophil
phagocytic WBC that circulates in blood and are attracted by signals from infected tissues; tends to self-destruct as they destroy foreign invaders, limiting life span to a few days
macrophage
large, phagocytic WBC found in body tissues that destroys microorganisms in innate immunity and functions as an antigen presenting cell in adaptive immunity
leukocytes
white blood cells of the vertebrate immune system
dendritic cell
WBC that populates tissues that contact the environment, stimulates adaptive immunity against pathogens it encounters and engulfs
mast cell
WBC found in connective tissue that releases histamine to sites of damage, initiating inflammatory response
natural killer cell
WBC that circulates in the blood and detects abnormal cells, releases chemicals that causes cell death
main types of antimicrobial proteins
interferons and complement proteins
process of antimicrobial proteins
pathogen recognition —> release of proteins —> attack pathogen or impede production
interferons
antimicrobial protein that interferes with viruses and activate macrophages
complement proteins
proteins that circulate in an inactive state and are activated by substances on pathogen surfaces; can amplify inflammatory response, enhance phagocytosis, or lyse extracellular pathogens
inflammatory response
innate immune defense triggered by injury or infection of tissue involving the release of substances to promote swelling, enhance filtration of WBCs, & aid in tissue repair/destruction of invading pathogens
cytokines
small peptides that act as signaling molecules, regulate the function of other cells
role of macrophages in the inflammatory response
discharge specific cytokines that recruit neutrophils to site of damage
role of mast cells in the inflammatory response
release histamine to site of damage
What allows for increased influx of immune cells and dilution of toxins in the inflammatory response?
blood vessel dilation and increased permeability
What do activated complement proteins do in the inflammatory response?
promote more histamine release to attract more phagocytic cells to the site of damage
What does increased blood flow do in the inflammatory response?
produces redness, increased skin temp, & helps deliver antimicrobial proteins
What happens in the inflammatory response as a result of increased blood supply and more histamine release by activated complement proteins?
accumulation of pus
pus
fluid rich in WBCs, dead pathogens, and debris from damaged tissue
main complications of the inflammatory response
fever and sepsis/septic shock
fever
systemic inflammatory response that is hypothesized to enhance phagocytosis and speed up tissue repair
sepsis
overwhelming inflammatory response that causes organ damage; increased leakiness of blood vessels, causing swelling and low blood pressure
barrier defenses of innate immunity
skin, mucous membranes, secretions
internal defenses of innate immunity
phagocytic cells, natural killer cells, antimicrobial proteins, inflammatory response
lymphocytes
type of WBC that mediates immune responses, two main types important to adaptive immunity are B and T cells
characteristics of the adaptive immune system
large diversity of lymphocytes & receptors, self-tolerance, B and T cell proliferation, immunological memory
antigen
substance that elicits an immune response by binding to receptors of B cells, antibodies, or T cells
antigen receptor
surface proteins on B and T cells that bind to antigens and initiate an adaptive immune response
When/how does recognition of foreign particles occur in the adaptive immune response?
B or T cell binds to an antigen via an antigen receptor
epitope
small, accessible region of an antigen to which an antigen receptor or antibody binds
clonal selection
process where 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
effector cells
short-lived cells that take effect immediately against an antigen and any pathogens producing that antigen
What is the B cell effector cell?
plasma cells
memory cells
long-lived cells that can give rise to effector cells if the same antigen is encountered later in the animal’s life, result of clonal selection
plasma cells
effector cells in B cells that secrete antibodies in adaptive immunity, arise from antigen-stimulated B cells, result of clonal selection
structure of T cell receptors
alpha and beta polypeptide chains, each with a constant (C) region and the tips form a variable (V) region that together form an antigen-binding site
What condition has to be met for antigen receptors of T cells to bind?
they bind only to antigen fragments that are displayed on the surface of host cells
major histocompatibility complex (MHC)
host protein that displays the antigen fragment on the cell surface for T cell antigen receptors
antigen presentation
display of an antigen fragment in an exposed groove of an MHC protein
main types of T cells
cytotoxic and helper
cytotoxic T cells
type of lymphocyte that, when activated, secretes toxic proteins to kill cells infected by viruses or other pathogens
helper T cells
type of T cell that, when activated, secretes cytokines that promote the response of B cells in the humoral response and cytotoxic T cells in the cell-mediated response
structure of B cell receptors
Y-shaped molecule with two identical heavy chains and two identical light chains, each chain has a constant (C) region and a variable (V) regions, the V regions of the heavy and light chains form the antigen-binding sites
How are B cells activated and what do the activated cells do?
activated by binding to an antigen, secrete soluble antibodies
antibodies
secreted form of B cell receptors, not membrane bound, provides direct defense against pathogens
types of adaptive immunity
cell-mediated or antibody-mediated
antibody-mediated (humoral) immune response
branch of adaptive immunity; involves activation of B cells and leads to production of antibodies, which help neutralize or eliminate toxins and pathogens in blood and lymph
cell-mediated immune response
branch of adaptive immunity; involves activation of cytotoxic T cells, which destroy infected host cells
steps of the cell-mediated response
cytotoxic T cells secrete perforin
cytotoxic T cells secrete granzymes
granzymes cause apoptosis
perforin
protein that perforates the cell membrane
What do granzymes do in the cell-mediated immune response?
secreted by cytotoxic T cells, enter the cell through the pores created by perforin
steps of the antibody-mediated immune response
B cells are activated by helper T cells or by binding to an antigen
B cells produce memory B cells and plasma cells (clonal selection)
What do plasma cells produce?
thousands of antibodies
methods that antibodies use to fight infection
neutralization, agglutination, precipitation, activation of complement proteins
Where are memory B cells found?
lymph nodes
primary immune response
initial adaptive immune response to an antigen, appears after 10-17 days, B and T cells produce effector cells
secondary immune response
adaptive immune response elicited on subsequent exposures to an antigen; faster, stronger, and longer responses; facilitated by memory B cells
active adaptive immunity
resistance built up following exposure to an antigen, can be natural (ex: caught pox) or artificial (ex: vaccination)
passive adaptive immunity
antibodies in the recipient are produced by another individual (ex: antibodies in breastmilk)
immunization
use of antigens artificially introduced into the body to generate an adaptive immune response and memory cell formation