Ch. 51 The Immune System in Animals Flashcards
pathogen
disease-causing organism
(ie) bacteria, parasite, microbe, virus or prion
immune system
the system whose primary function is to defend the host organism against pathogens
- includes several types of cells (leukocytes)
- lymph nodes & thymus
organs of the immune system
1) lymph nodes
2) thymus
observations biologists investigated about how animals stay healthy
1) wounds usually heal even if they become infected
2) most people who contract a bacterial/viral illness eventually recover w/out medication
3) people who acquire bacterial in viral infections and recover frequently do not contract the same disease again
immunity
a resistance to or protection against disease-causing pathogens
- prevents individuals from contracting disease more than once
immunization
the conferring of immunity to a particular disease by artificial means
(ie) vaccination
vaccination
artificially producing immunological memory against a pathogen by introducing a weakened/altered pathogen to prime the body’s immune system so it fights later infections effectively
Edward Jenner
physician who observed milkmaids did not get smallpox b/c they were exposed to cowpox
innate immunity
a set of barriers to infection & generic defenses against broad types of pathogens
- immediate response
- involves many leukocytes
- often activate an inflammatory response
- ready to respond to foreign invaders @ all times
- nonspecific
- responds in the same way to all antigens
antigen
any foreign molecule (often a protein) that can stimulate an innate or adaptive response by the immune system
adaptive immunity
immunity to a particular pathogen or antigen
- based on interactions btwn specific immune system cells & a specific antigen
- B & T cells
- specific
- diverse
- memory
- self-nonself recognition
(aka) adaptive immune response
* we get this from our mom
types of immunity
1) innate immunity
2) adaptive immunity
characteristics of innate immunity
- occurs in all animals
- has both cell-mediated & secreted components
- rapid response
- broadly specific response against types of pathogens
- response does not vary when infections recur (no memory)
- born w/
characteristics of adaptive immune
- occurs only in vertebrates
- has both cell-mediated & secreted components
- slow response
- specific response against pathogen strains
- response is more rapid & efficient when infection recur (memory)
- learned
barriers to invasion/entry
1) non-specific physical/chemical defenses
2) innate immunity (natural)
3) adaptive immunity (acquired)
* if pass #3, you’re screwed, you will die
types of barriers in the animal kingdom
1) insects - armored body
2) soft-bodied animals - covered w/ mucus
3) human skin - dead cells filled w/ keratin
how does the human skin act as a barrier against invasions?
1) shingled dead layer of cells filled w/ keratin acts as a protective layer
2) skin covered w/ oil (fatty acids), which lowers pH, making it difficult for pathogens to grow
mucus
a proteoglycan-rich solution secreted by epithelial cells
- serves as a barrier to protect surfaces from infection
how are gaps in the body protected?
*excluding mucous layers
via wax & lysozyme
wax
a class of lipid w/ extremely long, saturated hydrocarbon tails - harder & less greasy than fats
lysozyme
an enzyme that digests bacterial cell walls
- innate immunity
- occurs in lysozomes of phagocytes
- secreted in saliva, tears, mucus & egg white
flu virus
contain enzyme on their surface that disrupts the mucous lining of the respiratory tract
- sialic acid (originated from chickens)
- cross species disease
cells involved in the innate immune response
1) leukocytes
2) mast cells
3) macrophages
4) neutrophils
how are innate immune response leukocytes alerted by the presence of foreign invaders?
antibodies bind to antigens, labeling them as invaders
- binding cites are only found in invaders, not host cells
Innate response is nonspecific, but will respond to groups of pathogens such as _______ and ______
bacteria & fungi
pattern-recognition receptor
(leukocytes) a class of membrane proteins that bind to molecules commonly associated w/ foreign cells & viruses
- signal responses against broad types of pathogens
- innate immune response
- activated by pathogen-specific compounds
- serve as “on” switches by imitating cell response
(ie) Toll protein
Toll protein receptor (TLR)
“amazing”
acts as a receptor to signal a pathogen is present
- responds to antigens
- pattern-recognition receptors
(flies) signal production
1) fly detects a fungus infection: signal cascade activates secretion of antimicrobial peptides that act as antibodies
2) human TLR4 is activated, signal cascade promotes secretion of cytokines
3) when a virus attacks a cell, TLR7 detects signal promoting the secretion of a specific cytokine, interferon
cytokine
a group of signal proteins
- secreted by immune system
- stimulates leukocyte production
- recruits cells to site of infection, tissue repair & fever
- regulate type, intensity & duration of an immune response
(1st response) inflammatory / innate response in humans
- occurs @ site of an injury
1) skin breaks, pathogens enter a wound
2) platelets release blood-clotting proteins @ wound site
3) wounded tissues & macrophages @ wound site secrete chemokines, signaling molecules that assault immune cells by forming a gradient to mark the path to the site
4) mast cells release chemical messengers that constrict blood vessels near the wound–reducing blood flow & thus blood loss
5) neutrophils & macrophages remove pathogens by phagocytosis
6) macrophage secrete cytokines that attract other immune system cells to the site & activate cells involved in tissue repair; also induce fever
platelet
a small membrane-bound cell fragment in vertebrate blood
- FCN: blood clotting
- derived from large cells in the bone marrow
chemokine
a subset of cytokine
- acts as a chemical signal
- attracts leukocytes to a site of tissue injury or infection
- produced by: injured tissues & macrophages in tissues
- received by neutrophils & macrophages
- mark path to wound
- promote division & increased permeability of blood vessels
mast cell
a type of leukocyte
- stationary (embedded in tissue)
- triggers inflammatory response
- triggers secretion of histamine to infection or injury
- important in allergic response & defense against parasites
histamine
a molecule released from mast cells during an inflammatory response
- high concentrations: blood vessels constrict, reduced blood loss from tissue damage
- produced by: mast cells
- received by: blood vessels
neutrophil
a type of leukocyte
- capable of moving through body tissues
- engulfs & ingests pathogens & otro foreign particles
- secretes various compounds that attack bacteria & fungi
macrophage
a type of leukocyte
- participates in inflammatory response
- secretes cytokines & phagocitizing invading pathogens & apoptotic cells
- serves as an antigen-presenting cell to activate lymphocytes
phagocytosis
uptake by a cell of small particles or cells by invagination & pinching off of the plasma membrane to form small, membrane-bound vesicles
- engulf & digest
fever
elevated body temperature that aids in healing
innate immunity in invertebrates
innate responses make up the entire immune system observed in millions of species of invertebrates
- not fully functioning
examples of invertebrate innate immunity
1) cells respond to pathogen by synthesizing &;secreting peptides w/ potent antibacterial or antifungal properties
2) sea stars have specialized cells similar to neutrophils & macrophages; secrete cytokines or engulf & destroy pathogens by phagocytosis
key characteristics of the adaptive immune response
1) specificity
2) diversity
3) memory
4) self-nonself recognition
antibody
a protein produced by B cells
- bind to a specific part of an antigen
- tags antigen for removal by the immune system
- consist of 2 light chains & heavy chains
(aka) immunoglobulin
specific
adaptive immune response
antibodies & otro components of the adaptive immune system bind only to specific sites on specific antigens
diversity
adaptive immune response
the adaptive response recognizes an almost limitless array of antigens
memory
adaptive immune response
the adaptive response can be reactivated quickly if it recognizes antigens from a previous infection
self-nonself recognition
adaptive immune response
molecules that are produced by an individual do not act as antigens, so the adaptive immune system can distinguish btwn self and nonself
*major problem in organ transplants
lymphocyte
a cell that circulates through the bloodstream & lymphatic system
- responsible for development of adaptive immunity
- produced in bone marrow
- may also originate in the spleen
- belongs to either B cells or T cells
*unspecific like undergrad
inflamed lymph nodes
- sick
- high B or T cell concentration
*massage increase B or T cell movement, decreasing inflammation
types of lymphocytes
1) B cells
2) T cells
bone marrow
the soft tissue filling the inside of large bones
- contains stem cells that develop into RBC & leukocytes throughout life
spleen
a dark red organ found near the stomach of most vertebrates
- filters blood
- stores extra RBC in case of emergency
- plays a role in immunity
- lymphocytes may originate from here
B cell
a type of lymphocyte
- matures in the bone marrow (most animals) or bursa (birds)
- responsible for adaptive immunity
- produces antibodies
- functions in antigen presentation
*specializes in bone marrow like specialization in grad school
T cell
a type of lymphocyte
- matures in the thymus
- responsible for adaptive immunity
- involved in activation of B cells
- destroys infected cells
*specializes in thymus like specialization in grad school
B cells in chickens are produced in the _____.
bursa
bursa
organ that is necessary for B cell development in birds
bursa-dependent B cells
produces antiodies
lymph nodes
any of many small, oval structures that lymph moves through in the lymphatic system
- filters lymph
- screens lymph for pathogens & otro antigens
- major sites of lymphocyte activation
- small organs located throughout the body
lymphatic ducts
thin-walled, branching tubules that transport lymph throughout the body in the lymphatic system
lymphatic system
a body-wide network of thin-walled ducts (or vessels) & lymph nodes
- separate from circulatory system
- collects excess fluid from body tissues & returns it to the blood
- fcns as part of the immune system
parts of B- or T-cell receptors
1) light chain
2) heavy chain
characteristics of the light chain
1) dozens of different V segments
2) several different joining (J) segments
3) a single constant (C) segment
characteristics of the heavy chain
contains the diversity (D) segments
lymphocyte origin
bone marrow or bursa
lymphocyte maturation
1) B cells = bone marrow
2) T cells = thymus
lymphocyte activation
1) spleen
2) lymph nodes
lymphocyte transport
1) blood
2) secondary organs of the immune system: spleen, lymph nodes and lymphatic ducts
lymphatic duct
a thin-walled, branching tubule that transports lymph throughout the body and along w/ lymph nodes
- make up lymphatic system
immunoglobulin (Ig)
any of the class of proteins that are structurally related to anitbodies
IgG
1) structure: monomer
2) circulates in blood and interstitial fluid
3) protects against bacteria, viruses and toxins
* most abundant type of secreted antibody
IgD
1) structure: monomer
2) present on membranes of immature B cells
3) rarely secreted
4) serves as BCR
IgE
1) structure: monomer
2) secreted in minute amounts
3) involved in response to parasitic worms
4) responsible for hypersensitive reaction that produces allergies
IgA
1) structure: dimer
2) most common antibody in breast milk, tears, saliva, and the mucus lining the respiratory and digestive tracts
3) prevents bacteria/viruses from attaching to mucous membranes
4) helps immunize breastfed newborns
IgM
1) structure: pentamer
2) 1st type of secreted antibody to appear during an infection
3) binds many antigens @ once
4) effective at clumping viruses and bacteria so that they can be killed
5) monomeric form serves as BCR
gene recombination
the molecular mechanism responsible for the adaptive immune system’s specificity and diversity
self molecule
a molecule that is synthesized by an organism
- a normal part of cell and/or body
- receptor would trigger an immune response
nonself
foreign molecule
how is autoimmunity avoided using self molecules?
anti-self T and B-cells are destroyed before they mature
examples of autoimmunity
1) multiple sclerosis (MS)
2) rheumatoid arthritis
3) Type I diabetes mellitus
multiple sclerosis (MS)
a human autoimmune disease in which the immune system attacks the myelin sheaths that insulate axons of neurons
rheumatoid arthritis
an autoimmune disease in which T cells and antibodies alter the lining of joints
Type I diabetes mellitus
an autoimmune disease that affects the production of insulin
- T cells attack/kill insulin-secreting cells in the pancreas
- inability to regulate blood glucose levels
- high blood glucose levels
- huge amounts of glucose-containing urine
clone-selection theory
the dominant explanation of the generation of an adaptive immune response
the immune system retains a vast pool of inactive lymphocytes, each w/ a unique receptor for a unique epitope
- lymphocytes that encounter their complementary epitopes are stimulate to divided (selected and cloned), producing daughter cells that combat infection and confer immunity
central claims of the clonal-selection theory
1) each lymphocyte has thousands of copies of a unique receptor on its surface; the receptor, a membrane protein, recognizes only one antigen
2) lymphocyte is activated when it binds to its specific antigen
3) an activated lymphocyte divides and makes many identical copies of itself; in this way, specific cells are selected and cloned in response to an infection
4) some of the cloned cells descended from an activated lymphocyte persist after the pathogen is eliminated and allow a rapid response if the infection recurs
summary of clonal selection theory
1) antigens recognized by receptors on lymphocytes
2) lymphocytes are activated when receptors bind to an antigen
3) activated lymphocytes are activated
4) activated lymphocytes endure
dendritic cell
a type of leukocyte that ingests and digests foreign antigens
- moves to a lymph node
- presents the antigens’ epitopes, in the context of MHC proteins on its membrane, to CD4 and CD8 T cells
- contain MHC proteins
major histocompatibility (MHC) proteins
antigen-presenting proteins that are involved in marking cells as self and in antigen presentation to T cells
- have a groove where small peptide fragments (8-20 amino acids) bind
- 2 classes
classes of MHC
1) class I
2) class Ii
class I MHC protein
a type of MHC protein present on the plasma membrane of virtually all nucleated cells
- FCN: presenting antigen to CD8 T cells
binds antigens inside the ER
class II MHC protein
a type of MHC protein present only on the plasma membrane of certain cells in the immune response
- present on dendritic cells, macrophages, and B cells
- FCN: presenting epitopes of antigens to CD4 Tcells
binds antigens inside ENDOSOMES
when dendritic cells arrive @ wound, the following actions occur
1) dendritic cells ingest antigens present @ the wound
2) the antigen enters a membrane-bound compartment inside the cell
3) an enzyme complex breaks the proteins into pieces, which then become bound to an MHC protein
4) the MHC-antigen complex is transported to the cells surface
5) the MHC-antigen complex is displayed on the cell surface
endosome
a membrane-bound compartment inside a cell
- transport molecules between plasma membrane to the lysosome
- designed to chop proteins
MHC antigen presentation
1) dendritic cell ingests antigen via phagocytosis
2) enzymes break antigen into peptide fragments
3) peptides are loaded into MHC in endosomes
4) MHC-peptide complex is transported to cell surface
5) MHC protein presents peptide on cell surface
CD4
a membrane protein on the surface of some T cells in humans
- CD4 T cells give rise to helper T cells
- interact w/ MHC, class II bound antigens
CD8
a membrane protein on the surface of some T cells in humans
- CD8 T cells give rise to cytotoxicT cells
- interact w/ MHC, class I bound antigens
how are lymphocytes activated?
begins when antigens are taken up by a specific type of leukocyte or an infected cell, cut into pieces, packaged w/ specific cell proteins, and transferred to the cell surface
cytotoxic T cell
a type of CD8 Tcell
- induces apoptosis in infected/cancerous cells
- recognizes target cells via interactions w/ complementary class I MHC-peptide complexes
- interact only w/ host cells that display antiggens presented on class I MHC proteins
- signals cell is infected and should be sacrificed
“kill me”
“cell-poison”
(aka) killer T cell
helper T cell
a CD4 effector T cell that secretes cytokines
- promotes activation of other lymphocytes
- activated by interacting w/ complementary class II MHC-peptide complexes on the surface of antigen-presenting cells (ie. dendritic cells)
“activate now”
(aka) effector T cell
clonal expansion
process of dividing to produce a series of genetically identical daughter cells
- leads to a large lymphocyte population capable of responding to a specific antigen
types of helper T cells
1) TH1
2) TH2
TH1
a type of helper T cell
- activates killer cells
TH2
a type of helper T cell
- activates B cells
process of B-cell activation
1) a B cell encounters and binds to a foreign protein in a lymph node or the spleen - B cell internalizes and processes the molecule, and presents it on the cell surface by an MHC class II protein
2) the B cell activates the helper T cell when the antigen complex interacts w/ receptors on the helper T cell
3) the activated helper T cell releases cytokines, which activate the B cell
4) activated B cell divides; some daughter cells differentiate into plasma cells, which produce large quantities of antibodies
basic B-cell activation process
1) B cell recognizes invader
2) B cell stimulates active T cell
3) B cell is activated by helper T cell
4) activated B cell divides, produces plasma cells, which produce antibodies
antibodies will bind to antigens and mark them for destruction
mechanism for the adaptive immune response
1) cell-mediated involves TH1 and cytoxic T cells, occurs by cell-to-cell communication
2) humoral response promoted by TH2 cells, which secrete antibodies into blood and lymph
humoral response
type of immune response
- mediated through production/secretion of antibodies, complement proteins and other soluble factors that eliminate extracellular pathogens
- antibodies coat free virus particles so that they cannot infect cells
plasma cell
a B cell that produces large quantities of antibodies after being activated by interacting w/ antigen and a CD4 T cell via peptide presentation
(aka) effector B cell
result of antibodies coating foreign cells
agglutination
agglutination
clumping of cells or viruses by antibodies or other cross-linking molecules
benefits of agglutination
1) agglutinated cells are more readily phagocytoized by macrophages
2) these cells stimulate a lethal group of proteins called the complement system
complement system
a set of proteins that circulate in the bloodstream
- assembles antigen-antibody complex
- can destroy bacteria by forming holes in the bacterial plasma membrane
ways bound antibodies eliminate pathogens
1) opsonizaiton
2) neutralization
3) agglutination
4) co-stimulation of complement proteins
opsonization
“preparation for eating”
coating of the pathogen and its destruction by phagocytes
neutralization
“block from interaction”
blocking of coated cells from interacting w/ host cells
agglutination
“gluing together”
clumping of antigens by antibodies
co-stimulation of complement proteins
activation of a group of proteins called the complement system
major ways the immune system eliminates viruses
1) cell-mediated response
2) humoral response
cell-mediated response
a type of immune response
- generation of cytotoxic T cells from CD8 T cells
- defends against pathogen-infected cells, cancer cells and transplanted cells
- prevents new generations of virus particles from maturing
why do some transplanted tissues/organs get rejected?
transplanted tissues/organs contain antigens that are recognized as foreign, creating an immune response
- leading to rejection of the organ and possible death of the patient
to prevent strong immune reactions, physicians do 2 things
1) obtain the organ to be transplanted from a sibling or other donor whose MHC proteins are extremely similar to those of the recipient
2) treat the recipient w/ drugs that suppress the immune response
memory cell
a type of lymphocyte
- responsible for maintaining immunity for years or decades after an infection
- descended from a B or T cell activated during a previous infection or vaccination
- secondary immune response
- immunological memory
primary immune response
an adaptive immune response to a pathogen that the immune system has not encountered before
secondary immune response
the adaptive immune response to a pathogen that the immune system has encountered before
- normally much faster and more efficient than the primary response (due to immunological memory)
immunological memory
the ability of the immune system to “remember” an antigen and mount a rapid, effective adaptive immune response to a pathogen encountered years or decades earlier
- based on formation of memory lymphocytes
epitope
a small region of a particular antigen to which an antibody,B-cell receptor, or T-cell receptor binds
somatic hypermutation
mutation that occurs in the variable regions of immunoglobulin genes when B cells are first activated and in memory cells
- results in novel variation in the receptors that bind to antigens
vaccine
a preparation designed to stimulate an immune response against a particular pathogen w/out causing illness
types of vaccines
1) subunit vaccine
2) inactivated virus
3) attenuated or “live” virus
subunit vaccine
consist of isolated viral proteins
(ie) hepatitisu B and influenza
inactivated virus
virus that has been damaged by chemical treatments or exposure to ultraviolet light
- do not cause infections
- are antigenic (changes shape to affect host)
(ie) hepatitis A and polie
attenuated virus
“live”
consist of complete virus particles that have lost the ability to grow rapidly in their normal host cell
(ie) smallpox, polio, measles
vaccination
artificially producing immunological memory against a pathogen by using isolated antigens or altered versions of the pathogen to stimulate an adaptive immune response in the absence of disease
human immunodeficiency virus (HIV)
a retrovirus that causes acquired immune deficiency syndrome (AIDS) in humans
- progressive loss of CD4 T cells
- kills CD4 T cells and macrophages
- eventually turns into AIDs
acquired immune deficiency syndrome (AIDs)
a human disease characterized by death of immune system cells (helper T cells) and subsequent vulnerability to other infections
- caused by HIV
allergy
an IgE-mediated abnormal over-reactive response to an antigen
- usually characterized by dilation of blood vessels, contraction of smooth muscle cells, and increase activity of mucus-secreting cells
allergen
any molecule (antigen) that triggers an allergic response (allergy)
hypersensitive reaction
an intense allergic response by cells that have been sensitized by previous exposure to an allergen
- due to presence of IgE antibodies
severe combined immunodeficiency disease (SCID)
a immune deficiency
- caused by mutations on the X chromosomes
- mutation interferes w/ development of T cells
Omenn syndrome
a genetic defect that interferes w/ the recombinant DNA responsible for the T-cell and B-cell receptor production
