Chapter 24: The immune system Flashcards
(107 cards)
1
Q
What is immunity?
A
The body’s ability to protect itself
2
Q
What does the immune system distinguish when carrying out its function?
A
By distinguishing “self” (The body’s normal cells) from “nonself”
3
Q
What is “nonself” cells?
A
Nonself includes viruses, bacteria, parasites, allergens, and other disease-causing pathogens, in addition to any of our own cells that have become defective and threaten to do harm, such as become cancer
4
Q
What is the body’s first line of defence against external pathogens?
A
includes physical, chemical, and mechanical barriers, such as skin, tears, mucus, and stomach acid
5
Q
what happens if pathogens evade the protective barriers?
A
The body initiates an immediate internal immune response with four basic steps:
1.) detection and identification of the pathogen
2.) communication with other immune cells to rally an organised response
3.) recruitment of assistance and coordination of the response among all participants
4.) destruction or suppression of the pathogen
6
Q
What are immunogens?
A
Substances that trigger the body’s immune response
7
Q
what are antigens ?
A
immunogens that react with products of the immune response
8
Q
what is the internal immune response carried out by?
A
Leukocytes, and is heavily dependent on cell-to-cell communication
9
Q
What does chemical communication in the immune system include?
A
substances released by damaged or dying cells, as well as cytokines
10
Q
What are cytokines?
A
protein signal molecules released by one cell that affect the growth or activity of another cell
11
Q
The immune system is the primary user of contact-dependent signalling that occurs when the surface receptors on one cell recognise and bind to surface receptors on another cell, true or false?
A
True
12
Q
The internal immune response can be divided into two phases:
A
A rapid innate response, and a slower adaptive response
13
Q
describe innate immunity
A
-present from birth
-is the body’s immediate immune response to invasion
-not specific to one pathogen, so it begins within minutes to hours
-an innate immune response to a pathogen is not remembered by the immune system and must be triggered anew with each exposure
14
Q
Describe the cells for the rapid innate immune response
A
-circulating and stationary leukocytes that are genetically programmed to respond to a broad range of material that they identify as foreign
15
Q
What happens when certain types of leukocytes identify bacterium as a pathogen, and what are those leukocytes?
A
-Called phagocytes, when phagocytes identify the bacterium as a pathogen, they ingest it via phagocytosis and digest it.
-Some types of phagocytes then display bits of disgusted pathogens on their cell surface to attract cells involved in the adaptive immune response
16
Q
What are the cells that display bits of digested pathogens on their cell surface to attraction cells involved in the adaptive immune response called?
A
antigen-presenting cells (APCs)
17
Q
describe adaptive immunity
A
-directed at particular invaders
-the body’s specific immune response
-steps needed to launch a specific immune response following first exposure to a pathogen may take days to weeks –> however, upon re-exposure certain immune cells called memory cells “remember” their prior exposure to the pathogen and react more rapidly.
18
Q
what can adaptive immunity be divided into?
A
cell-mediated immunity and antibody-mediated immunity
19
Q
what is cell-mediated immunity?
A
requires contact-dependent signalling between an immune cell and receptor on its target cell
20
Q
what is antibody-meditated immunity (aka humoral immunity)?
A
-uses antibodies (proteins secreted by immune cells) to carry out the immune response
-antibodies bind to foreign substances to disable them or make the more visible to the cells of the immune system
21
Q
is the innate and adaptive immune response separate or do they overlap?
A
-overlap, they are interconnected parts of a single process
-innate response is the more rapid response, but it does not target a specific invader. It is reinforced by the antigen-specific adaptive response, which amplifies the efficacy of the innate response
22
Q
what are the three major functions the immune system serves?
A
-tries to recognise and remove abnormal “self” cells created when normal cell growth and development go wrong
-it removes dead or damaged cells, as well as old red blood cells. Scavenger cells of the immune system patrol the extracellular compartment, gobbling up and digesting dead or dying cells
-it protects the body from disease-causing pathogens. Microorganisms (microbes) that act as pathogens include bacteria and viruses, fungi and one-celled protozoans. Larger pathogens include multicellular parasites
23
Q
What are the two anatomical components of the immune system?
A
lymphoid tissues and the cells responsible for the immune response
24
Q
Where is the immune system positioned anatomically?
A
Positioned wherever the pathogens are most likely to enter the body. For example, mucous membranes of the oral cavity have higher concentrations of immune cells than the tissue surrounding skeletal muscles of the leg.
25
where are lymphoid tissues found?
found all over the body
26
What are the primary lymphoid tissues?
The primary lymphoid tissues are:
-thymus gland
-bone marrow
(Both organs are sires where cells involved in the immune response form and mature)
27
What are secondary lymphoid tissues?
-in the secondary lymphoid tissues immune cells interact with pathogens and initiate a response
-secondary tissues are divided into encapsulated tissues and unencapsulated diffuse lymphoid tissues
28
What are the encapsulated lymphoid tissues?
-Spleen and Lymph nodes
-both spleen and lymph nodes have fibrous collagenous capsule walls and immune cells positioned so that they monitor the extracellular compartment for foreign invader -- phagocytic cells in the spleen also trap and remove aging red blood cells
29
The lymph nodes are part of the...
lymphatic circulation, which is closely associated with capillaries of the cardiovascular system.
30
What are the unencapsulated diffuse lymphoid tissues?
-Are aggregations of immune cells that appear in other organs and tissues of the body
-they include cells in the skin and the tonsils o the posterior nasopharynx as well as cells associated with mucosal surfaces exposed to the external environment -- The latter are known collectively as mucosa-associated lymphoid tissue (MALT)
31
What are the subgroups of MALT and where are they positioned?
-gut-associated lymphoid tissue (GALT) (lies just under the epithelium of the oesophagus and intestines
-clusters of lymphoid tissue associated with the respiratory, urinary, and reproductive tracts
-in each location, the immune cells are positioned to intercept invading pathogens before they get into the general circulation.
-because of the large surface area of the digestive tract epithelium, some authorities consider GALT to be the body's largest immune organ
32
What are leukocytes (or white blood cells)?
-Primary cell type responsible for immune responses
-although leukocytes circulate in the blood, they also leave the capillaries and function extravascularly (outside the vessels)
-some types of leukocytes can live out in the tissues for several months but other may only like for only hours or day
33
What are the types of leukocytes?
1.) Basophils in the blood and the related mast cells in the tissues
2.) eosinophils
3.) neutrophils
4.) monocytes and their derivative macrophages
5.) dendritic cells
6.) lymphocytes and their derivative plasma cells
(dendritic cells and mast cells are not usually found in the blood, and therefore are often excluded from discussions of leukocytes in blood)
34
describe granulocytes
-A morphological group of leukocytes
-white blood cells whose cytoplasm's contains prominent granules
-granulocytes include: basophils, eosinophils, and neutrophils
- the cell names come from the staining properties of the granules --> basophil granules stain dark blue with basic (alkaline) dye, and eosinophil granules stain dark pink with the acidic dye eosin, and neutrophil granules do not stain darkly with standard blood stains and are therefore "neutral".
- in all three types of granulocytes, the activated leukocyte releases its granule contents by exocytosis, a process known as degranulation
35
What are the two functional groups of leukocytes? And describe them.
-phagocytes and antigen-presenting cells
-phagocytes ingest material from the extracellular fluid using a large vesicle --> include neutrophils, macrophages, dendritic cells
-antigen-presenting cells (APCs) have the ability to display bits of antigen on their surface as a signal to other immune cells --> primary APCs are the macrophages and dendritic cells
36
describe basophils and mast cells
-basophils are rare in the circulation but are easily recognised in a stained blood smear by the large, dark blue granules in their cytoplasm
-basophils are related to the mast cells of tissues
-mast cells are concentrated in the connective tissues of skin, lungs, and the gastrointestinal tract; both locations where they are ideally situated to intercept pathogens
-both basophils and mast cells release chemicals that contribute to inflammation and the innate immune response
37
describe eosinophils
-easily recognisable by the bright pink-staining granules in their cytoplasm
-normally, few eosinophils are found in the peripheral circulation
-most functioning eosinophils are found in the digestive tract, lungs, urinary and genital epithelia, and connective tissue of the skin --> these locations reflect their role in defence against parasitic invaders
-attach to large antibody-coated parasites, such as blood fluke Schistosoma, and release substances from their granules that damage or kill the parasites
-Also participate in allergic reactions, where they contribute to inflammation and tissue damage by releasing toxic enzymes and oxidative substances
38
Describe neutrophils
-phagocytic cells that typically ingest and kill 5-20 bacteria during their short, programmed life span of one or two days
-most abundant white blood cells (50-70% of the total) and are most easily identified by a segment nucleus made up of three to five lobes connected by thin strands of nuclear material
-because of the segmented nucleus, neutrophils are also called polymorphonuclear leukocytes
-immature neutrophils, occasionally found in the circulation, can be identified by the horseshoe-shaped nucleus. These immature neutrophiles go by the nicknames of "bond" and "stabs".
-neutrophils, like other blood cell, are formed in the bone marrow and released into the circulation.
-most neutrophils remain in the blood but can leave the circulation if attracted to an extravascular site of damage or infection
-in addition to ingesting bacteria and foreign particles, neutrophils release a variety of cytokines, including fever-causing pyrogens and chemical mediators of the inflammatory response
39
describe monocytes and macrophages
-monocytes are the precursor cells of tissue macrophages
-monocytes are not very common in the blood (1-6% of all white blood cells)
-only spend eight hours in their transit from the bone marrow to their permanent positions in the tissues
-once in the tissues, monocytes enlarge and differentiate into phagocytic macrophages
-some tissue macrophages patrol the tissues, creeping along amoeboid motion. Others find a location and remain fixed in place. In either case, macrophages are the primary scavenges within tissues
-They are larger and more effective than neutrophils, ingesting up to 100 bacteria during their life span.
-Macrophages also remove larger particles, such as old red blood cells and dead neutrophils
-histiocytes in skin, Kupffer cells in liver, osteoclasts in bone, microglia in the brain, and reticuloendothelial cells in the spleen are all name for specialised macrophages
-The new name for the reticuloendothelial system is the mononuclear phagocyte system, a term that refers both to macrophages in the tissues and to their parent monocytes circulating in the blood
40
describe dendritic cells
-are macrophages relatives characterised by long, thin processes that resemble the dendrites of neurons
-found in the skin (where they are called Langerhans cells) and in various organs
-They play a key role in linking innate and adaptive immune responses by displaying bits of foreign antigen that they have ingested and processed
41
describe lymphocytes
-lymphocytes and their derivative plasma cells are the key cells that mediate the specific adaptive immune response of the body
-the adult body contains a trillion lymphocytes at any one time
- only 5% of these are found in the circulation, where they constitute 20-35% of all white blood cells
-Most lymphocytes are found in lymphoid tissues, where they are especially likely to encounter invaders
42
Where does white blood cell development (or haematopoiesis) begin?
-in the bone marrow under the influence of cytokines called colony-stimulating factors and interleukins
43
during embryonic development, one set of immature lymphocyte precursor cells, the T lymphocytes (T cells)...
migrates from the bone marrow to the thymus gland, where they mature
44
during embryonic development b lymphocytes (B cells)...
remains in the bone marrow
45
What category does natural killer (NK) cells form and where do they develop?
-form a third category of lymphocytes (T cells and B cells are the others)
-develop in bone marrows as well as in other tissues
46
activated B lymphocytes differentiate...
primarily into specialised plasma cells that secrete antibodies
47
What do antibody (aka immunoglobulins) molecules do?
-Work against foreign bodies (antigens)
-the alternate name, immunoglobulins, describes what the molecules are: globular proteins that participate in the adaptive immune response
48
which cells play important roles in defence against intracellular pathogens, such as viruses?
T cells and NK cells
49
how many antigens do B and T cells bind to?
Each B and T cell binds only to one particular antigen
50
What is a clone?
all lymphocytes that bind that particular antigen form a group known as a clone
51
how can the body store both the number and variety of lymphocytes needed for adequate defence?
The immune system keeps only a few cells of each lymphocytes clone on hand. If a pathogen appears, the clone whose cell receptors match the pathogen quickly reproduces to provide the additional cells needed
52
What are the primary effector cell for the antigen-specific of adaptive immunity?
Lymphocytes
53
Discuss how lymphocytes look on a microscopic and molecular level
-on a microscopic level, all lymphocytes look alike
-at the molecular level, the different cell types can be distinguished from one another by their membrane receptors
54
What is self-tolerance?
The lack of immune response by lymphocytes to cells of the body, it begins during embryonic development
55
Where do the specificity of lymphocyte clones resides?
in the proteins that become cell surface receptors or antibodies
56
describe what happens during development so ensure the formation of clones
During development, a complex genetic mechanism rearranges the sequence of amino acids in the receptor protein to form millions of different combinations. Some of these combinations will not bind to the body's own components, or self-antigens, so those cells that do not react with self-antigens go on to form clones
57
Describe what happens when lymphocytes develop with receptor proteins that will recognise self-antigens
-it would be damaging to the body if these lymphocytes persisted because they would create an immune response against the body- an autoimmune response
-When these self-reactive lymphocytes combine with self-antigen in the primary lymphoid tissues, they are immediately targeted for destruction (negative selection) by apoptosis.
-The removal of clones of self-reactive lymphocytes is known as clonal deletion
58
describe the hygiene hypothesis
Over the past century, as developed countries eradicated many parasitic, viral and bacterial diseases they have seen an increase in autoimmune and allergic diseases, such as asthma, food allergies, and irritable bowel syndrome (IBS). One hypothesis proposed to explain this observation is the hygiene hypothesis, which says that challenging the immune system early in like strengthens it, and that a too-clean environment contributes to a weakened immune system.
-one group of scientists has proposed that it is not lack of exposure to microbes that is at fault but lack of diversity in human microbiome that is the blame
59
What are chemotaxins?
-signal molecules that attract leukocytes to help fight infection
60
What are opsonins?
-molecules that coat foreign particles to make them visible "food" for phagocytic leukocytes
61
Some cytokines act as pyrogens that...
raise body temperature by altering the hypothalamic setpoint
62
What is the acute phase?
Time immediately following an injury or pathogen invasion
63
What happens in the acute phase?
-body responds by increasing the concentration of various plasma proteins
-some of these proteins, produced mostly by the liver, are given the general name of acute-phase proteins
-include molecules that act as opsonins by coating pathogens; enzyme inhibitors that help prevent tissue damage; and C-reactive protein (CRP)
-Normally, the levels of acute-phase proteins decline to normal as the immune response proceeds, but in chronic inflammatory diseases, such as rheumatoid arthritis, elevated levels of acute-phase proteins may persist.
- increases levels of CRP, for example, are also associated atherosclerosis and increases risk of coronary heart disease
64
Where is histamine primarily found? and what is its role?
in the granules of mast cells and basophils, and it is the active molecule that initiates the inflammatory response when mast cells degranulate
65
What does histamines actions do?
-brings more leukocytes to the injury site to kill bacteria and remove cellular debris
-it does this by dilating blood vessels, which increases blood flow to the area, and by opening pores in capillaries
-making capillaries more leaky also allows plasma proteins to escape into the interstitial space, pulling water with them and leading to tissue edema (swelling).
-The result of histamine release is a hot, red, swollen area around a wound or infection site
66
What is complement proteins?
-a collective term for a group of more than 25 plasma proteins
67
the complement cascade is similar to...
the blood coagulation cascade
68
describe complement proteins
-they are secreted in inactive forms that are activated as the cascade proceeds
-intermediates of the complement cascade act as opsonins, chemical attractants for leukocytes, and agents that cause mast cell degranulation
-complement cascade terminates with the formation of membrane attack complex, a group of lipid-soluble proteins that insert themselves into the cell membranes of pathogens and virus-infected cells and form giant pores --> these pores allow water and ions to enter the pathogens cells. As a result, the cells swell and lyse
69
Adaptive immunity is requires the presentation of pathogen antigen to immune cells so they can respond to destroy or suppress that particular pathogens. Three groups of molecules participate in this process which are:
-Major histocompatibility complex (MHC)
-antibodies
-T-cell receptors
70
Antigen presentation is the job of...
membrane proteins known as major histocompatibility (MHC)
71
Recognition of antigen is the responsibility of...
B and T lymphocyte receptors
72
MHCs are a family of...
membrane protein complexes encoded by a specific set of genes
73
every nucleated cell of the body has MHC...
class I molecules on its membrane
74
MHC class II molecules are found...
primarily on antigen-presenting cells (APCs), including macrophages and dendritic cells
75
describe MHCs
-MHC proteins combine with peptide fragments of antigens that have been digested within the cell
-The MHC-antigen complex is then inserted into the cell membrane so that the antigen is visible on the extracellular surface.
-contact-dependent signalling occurs when the MHC-antigen complex interacts with the T-cell immune receptor
-free antigen in the extracellular fluid cannot bind to unoccupied MHC receptors on the cell surface
-MHC proteins were named when they were discovered to play a role in rejecting foreign tissue following organ transplant
-all MHC proteins are related, but they vary from person to person because of the huge number of potential MHC variants people can inherit from their parents
-MHC are one reason tissues cannot be transplanted from one person to another without first establishing compatibility
76
B lymphocytes make...
antibodies
77
What are antibodies?
-proteins that bind antigens and make them more visible to the immune system
-because antibodies are not toxic, they cannot destroy antigens. Their primary role is to help the immune system react to specific antigens
78
what are T cell receptors?
-antigen-specific membrane proteins
-are not antibodies, although the proteins are closely related
-Bind only to MHC-antigen complexes on the surface of an antigen-presenting cell
79
Describe the basic antibody molecule
-has 4 polypeptide chains linked into a Y shape
-The arms contain the antigen-binding sites
-The stem of the Y-shaped molecule, the Fc region, determines the class to which the antibody belongs
- a hinge region between the arms and the stem allows flexible positioning of the arms as the antibody binds to the antigen
-each arm of the Y, or Fab region, consists of one light chain, and one heavy chain with one antigen-binding site
-in any given antibody molecule, the two light chains are identical and the two heavy chains are identical. However, the chains vary widely among different antibodies, giving the antibody its specificity.
-each B lymphocyte clone produces a unique antibody
80
What are the 5 general classes of antibodies (or immunoglobulins (Ig))?
-IgG, IgA, IgE, IgM, IgD
-antibodies collectively are known as gamma globulins
81
describe IgG antibodies
-make up 75% of plasma antibody in adults
-some maternal IgGs cross the placental membrane and give infants immunity in the first few months of life
-Some IgGs activate complement
82
describe IgA antibodies
-found in external secretions, such as saliva, tears, intestinal and bronchial mucus, and breast milk, where they bind to pathogens and flag them for phagocytosis if they reach the internal environment
83
describe IgE antibodies
-target parasites and are associated with allergic responses
-when mast cell receptors bind with IgEs and antigen, the mast cells degranulate and release chemical mediators, such as histamine
84
describe IgM antibodies
-associated with early immune responses to a pathogen
-IgMs strongly activate complement
-They are also the antibodies that react to antigens found on red blood cells
85
Describe IgD antibodies
-Proteins appear as receptors on the surface of B lymphocytes and help activate the B cells
86
Which immunoglobulins are secreted as polymers?
-IgM and IgA
- IgM is made up of five Y-shaped antibody molecules, and IgA has from one to four antibody molecules
87
describe the difference in structure of bacteria and viruses
bacteria - Cells. No organelles. Usually surrounded by cell wall. Some encapsulated bacteria produce an additional protective glycoprotein outer layer known as a capsule.
Virus - Not cells. Nucleic acid core enclosed in viral proteins called capsid. Some viruses add an envelope of phospholipid and protein made from the host's cell membrane and incorporate viral proteins into the envelope.
88
describe the different living conditions for bacteria and viruses
bacteria - most can survive and reproduce outside a host if they have the required nutrients, temperature, pH, and so on
virus - Parasitic. Must use intracellular machinery of a host cell to replicate. Eliminating pathogens in intracellular and extracellular compartments of the body requires different defence mechanisms
89
describe the genetic material of bacteria and viruses
Bacteria- singular circular DNA chromosome
virus - May be DNA or RNA
90
describe the susceptibility to drugs for bacteria and viruses
bacteria - most can be killed or suppressed by antibiotics. These drugs act directly on bacteria and destroy them or inhibit their growth
virus - cannot be killed with antibiotics. Some can be suppressed with antiviral drugs, which target specific stages of viral replication
91
Describe the replication of viruses
-viruses can only replicate inside host cells --> replication cycle of a virus begins when virus invades the host cell
-once inside and free of the capsid, the virus' nuclei acid takes over the host cell's resources to make new virus particles that can infect other cells --> some viruses kill the host cell
-some, like Herpes simplex type 1 and varicella-zoster virus, which cause cold sores and chicken pox, respectively, "hide out", in the host cell and replicate only sporadically
-other viruses incorporate their DNA into the host cell DNA --> viruses with this characteristic include human immunodeficiency virus (HIV) and oncogenic viruses (which cause cancer)
92
What lines of defence does the body have?
-has two lines of defence --> physical and chemical barriers, such as skin, first to try to keep pathogens out of the body's internal environment --> if this first line of defence fails, then the internal immune response takes over --> The internal immune response begins with the rapid but nonspecific innate responses, followed more slowly by adaptive response to specific antigens.
93
describe the barriers of the body as the first line of defence
-first line of defence is to exclude pathogens by physical, mechanical, and chemical barriers
-physical barriers of the body include skin, the protective mucous linings of the gastrointestinal and genitourinary tracts, and the ciliated epithelium of the respiratory tract
-digestive and respiratory systems are most vulnerable to microbial invasions because these regions have extensive areas of thin epithelium in direct contact with external environment
-in women, the reproductive tract is also vulnerable, but to a lesser degree. The opening to the uterus is normally sealed by a plug of mucus that keeps bacteria in the vagina from ascending into the uterine cavity
-secretions from exocrine glans and mechanical removal of pathogens assist the physical barriers
-in respiratory system, inhaled particulate matter is trapped by mucus lining the upper respiratory system. The mucus is then transported upward on the mucociliary escalator to be expelled or swallowed, or may be coughed out.
- swallowed pathogens may be disabled or killed by the acidity of the stomach
-respiratory tract secretions, saliva, and tears contain lysozyme, an enzyme with antibacterial activity.
- lysozyme attacks cell wall components of unencapsulated bacteria and breaks them down. However, it cannot digest the capsules of encapsulated bacteria. In the intestines, the presence of pathogens may trigger increased motility and secretory diarrhoea.
94
pathogens that get past the physical barriers of skin and mucous membranes trigger...
the innate immune response
95
innate immunity either...
clears the infection or contains it until the adaptive immune response is active
96
a key element of the innate immune response is its broad specificity, true or false
true
97
describe PAMPs
-some immune cells recognise classes of molecules that are unique to microorganisms, generally called pathogen-associated molecular patterns, or PAMPs.
-PAMPs bind to leukocyte pattern recognition receptors (PRRs) and activate responses that attempt to kill or ingest the invader
98
how are patrolling and stationary leukocytes attracted to areas of invasions?
By chemicals signals known as chemotaxins
99
what do chemotaxins include in their cell walls?
include bacterial toxins or cell wall components that act as PAMPs
100
besides chemotaxins what else indicates areas that need defending?
-products of tissue injury, such as fibrin and collagen fragments, may also indicate a location that need defending
-endogenous "danger signals" are sometimes called DAMPs, for danger-associated molecular patterns
-once on site, activated leukocytes secrete their own chemotaxic cytokines to bring additional leukocytes to the infection site
101
what are the primary phagocytic cells responsible for initial defence?
Tissue macrophages and neutrophils
102
how does circulating leukocytes leave the blood (extravasation)?
-By squeezing through pores in the capillary endothelium
103
what is pus?
-if an area of infection attracts a large number of leukocytes, the material we call pus may form
-This thick, whitish to greenish substance is a collection of living and dead neutrophils and macrophages, along with tissue fluid, cell debris, and other remnants of the immune process
104
What group are phagocytes part of?
Functional group of white blood cells that engulf and ingest their targets by phagocytosis
105
wkhat are the primary phagocytes of the innate response?
-neutrophils and macrophages
-dendritic cells, which link innate and adaptive immunity, are also phagocytic
106
what kind of event is phagocytosis?
-receptor-mediated event, which ensures only unwanted particles are ingested
107
