Histology: Innate & Adaptive Immunity Flashcards
(109 cards)
1
Q
What are neutrophils? (2)
A
50% of white blood cells
> first to respond against bacteria/viral invasion
> alert other cells in immune system to respond as well
2
Q
What are eosinophils? (3)
A
1% in blood stream
> respond to parasite(worms) infections
> role in allergy symptoms—> overreaction to mistaken invader-pollen
>highly concentrated in digestive tract
3
Q
What are basophils?
A
1% of white blood cells
> mount non-specific immune response to pathogens
4
Q
What are lymphocytes? (2)
A
> T-cells kill foreign invaders directly
> B-cells hum oral immunity, produce antibodies that “remember” an infection
5
Q
What are monocytes?
A
Monocytes: 5% of white blood cells
> important for migrating into tissues and cleaning up dead cells
6
Q
What is the process of blood clotting? (6)
A
- Blood vessel is damaged—> collagen becomes exposed
- Collagen exposure attracts platelets to the injured area
- Platelets aggregate & stick together to form a plug
- Platelet plug alone is not strong enough—> protein fibrinogen becomes exposed to unknown chemicals on outside of blood vessel and is turned to sticky fibrin proteins
- Fibrin Fibres form a sticky mesh allowing for other things to stick/attach to it—> reinforcing it even further
- This clot develops into a scab—> new skin forms beneath the scab until the scab degrades
7
Q
What is scleroderma? (4)
A
Chronic hardening and tightening of the skin and connective tissues
- Excessive production of fibrillar collagen
- Changes in the physical structure of connective tissue components
- Localised (non-systematic)- skin limited
- Systematic sclerosis- affect internal organs
8
Q
What happens when a hematopoietic stem cell divides?
A
- can divide indefinitely producing 1 daughter cell that remains a stem cell & another cell that adopts a specialised function
9
Q
What do stem cells replenish?
A
- Replenish body’s blood cell population
10
Q
-Cell division of stem cells from bone marrow give rise to 2 specialised sets of cells: (2)
A
> Lymphoid progenitor cells: give rise to immune cells—> Lymphocytes (B&T cells)
Myeloid progenitor creels: give rise to other immune cells(WBCs), erythrocytes & platelets
11
Q
What is innate & adaptive immunity?
A
↳ Innate & adaptive immunity -
Recognition & response rely on traits common to groups of pathogens :
Pathogens → agents that cause disease (bacteria, viruses, fungi etc.)
12
Q
Specialised dedicated cells of the ____ _____ enable animals to avoid or limit many infections.
A
immune system
13
Q
What does the first line of defence do?
A
° First lines of defence > help prevent pathogens from entering the body.
↳ integumentary system
↳ mucosa
14
Q
What are the 2 types of molecular recognition → that allow detection of foreign
molecules, particles } cells?
A
↳ innate recognition
↳ adaptive recognition
15
Q
What is innate immunity?
A
→ innate immunity : a defence active immediately upon infection
16
Q
What is adaptive immunity?
A
Adaptive immune response: activated after the innate response & develops more slowly.
17
Q
What are self-particles? (2)
A
• made by your body /part of
• found circulating blood / attached to different tissues
• should not be targeted he destroyed by the immune system
↳ ‘tolerance’
18
Q
What are non-self-particles? (2)
A
→ ‘foreign’} recognised as potentially harmful
• bacteria, viruses, parasites, pollen, dust, toxic chemicals 4 fungi
• infectious /pathogenic particles make proteins called Antigens
19
Q
What are non-self-particles? (2)
A
→ ‘foreign’} recognised as potentially harmful
• bacteria, viruses, parasites, pollen, dust, toxic chemicals 4 fungi
• infectious /pathogenic particles make proteins called Antigens
20
Q
What are antigens?
A
allow the human body to know that they intend to cause damage
• ‘name tag’ for each pathogen to announce its presence to the immune system
21
Q
What are cytokines? (3)
A
molecules used for cell -signaling / cell-to-cell communication
° similar to chemokines → can be used to communicate with neighboring /
distant cells to initiate an immune response
° used to trigger cell trafficking /movement to a specific area of body
22
Q
What are chemokines? (2)
A
type of cytokine
☐ released by infected cells
☐ infected host cells release chemokines in order to initiate an immune response } warn neighbouring cells of the threat
23
Q
What does innate immunity rely on? (3)
A
Relies on:
- Dedicated immune system cells—> enable animals to avoid/limit infections
- First lines of defence (integumentary system + mucosa)—> help prevent pathogens from
gaining entry into the body
- Two types of molecular recognition within the body—> allow detection of non-self (foreign) molecules, particles and cells
24
Q
What do barrier defences include? (4)
A
- include skin + mucous membranes of respiratory, urinary & reproductive tracts
- mucous—> traps + allows for removal of microbes
- many bodily fluids (saliva, mucous, tears)—> hostile to many microbes
- low pH of skin + digestive system—> prevents the growth of many bacteria
25
What do cellular defences include? (4)
- Lymphatic system
- Innate immune cells:
> Detect
> Devour
> Destroy
- Recognise groups of pathogens using Toll-like receptors (TLR’s)
- TLR’s—> recognise fragments of molecules and characteristics of a set of pathogens
26
What do phagocytes do? (2)
- Phagocytes circulate throughout the body, looking for potential threats, like bacteria and
viruses, to engulf and destroy.
- Security guards on patrol
27
What are the two main types of phagocytes?
Neutrophils
| Macrophages
28
Where do neutrophils circulate?
circulate in blood
29
Why are phagocytic cells classified as granulocytes?
- phagocytic cells that are also classified as granulocytes because they contain granules in their cytoplasm.
- granules are very toxic to bacteria and fungi, and cause them to stop proliferating or die on contact
30
What is the function of neutrophils?
- first cells to arrive at the site of an infection because there are so many of them in circulation at any given time
31
Where do macrophages reside?
- migrate through body/reside in organs + tissues
32
What is the function of macrophages? (3)
- can leave the circulatory system by moving across the walls of capillary vessels.
- ability to roam outside of the circulatory system is important—> allows macrophages to hunt pathogens with less limits
- release cytokines in order to signal and recruit other cells to an area with pathogens
33
What is the function of dendritic cells? (4)
- stimulate development of adaptive immunity
- antigen-presenting cells
- since dendritic cells are located in tissues that are common points for initial infection—> can identify threats and act as messengers for the rest of the immune system by antigen presentation
- act as bridge between the innate immune system and the
adaptive immune system
34
Where are dendritic cells located? (5)
- external environments through the skin
- inner mucosal lining of the nose
- lungs
- stomach
- intestines
35
What is the function of eosinophils? (4)
- discharge destructive enzymes against parasite
- granulocytes target multicellular parasites
- secrete a range of highly toxic proteins and free radicals that kill bacteria and parasites
- use of toxic proteins and free radicals also causes tissue damage during allergic reactions—> so activation and toxin release by eosinophils is highly regulated to prevent any unnecessary tissue
damage
36
Where are eosinophils located? (5)
- the thymus
- lower gastrointestinal tract
- ovaries, uterus
- spleen
- lymph nodes
37
Where are mast cells found? (2)
Found in mucous membranes and connective tissues
38
What is the function of mast cells? (4)
- important for wound healing and defense against pathogens via the inflammatory response
- when mast activated—> release cytokines and granules that contain chemical molecules to create an inflammatory cascade
- Mediators—> histamine, cause blood vessels to dilate, increasing blood flow and cell trafficking to the area of infection
- The cytokines released during this process act as a messenger service, alerting other immune cells, like neutrophils and macrophages, to make their way to the area of infection/ be on alert for circulating threats
39
What is the function of basophils? (3)
- granulocytes that attack multicellular parasites
- release histamine—> like mast cells
- use of histamine makes basophils and mast cells key players in mounting an allergic response
40
What are natural killer cells? (4)
- circulate throughout body + detect abnormal cells
- release chemicals leading to cell death—> inhibits spread of vitally infected/ cancerous cells
- do not attack pathogens directly—> destroy infected host cells in order to stop the spread of an infection
- Infected or compromised host cells can signal natural kill cells for destruction through the expression
of specific receptors and antigen presentation
41
What is the process of a local inflammatory response? (5)
- brought by molecules released upon injury + infection
- mast cells(immune cells found in connective tissue —> check above for more info) —> discharge cytokines(signalling molecules that recruit neutrophils to the site & release histamine(triggers blood vessels to dilate + become more permeable ) —> increasing blood supply which triggers inflammatory response
- cycles of signalling + response continues inflammation process
- enhanced blood flow to site—>helps deliver anti-microbial peptides
- results in accumulation of pus—>fluid rich in WBCs, dead pathogens & debris from damaged tissue
42
What is the end result of a local inflammatory response? (4)
—> pus + excess fluid taken up as lymph
—> fluid transported in body by lymphatic system
—> lymph nodes(throughout body): contain macrophages which engulf pathogens that enter lymph
—> Dendritic cells migrate to lymph nodes after interacting with pathogens & stimulate adaptive immunity
43
What can more extensive tissue damage/infection lead to?
- more extensive tissue damage/infection —> can lead to a systemic response (throughout body)
44
What do cells in injured/infected tissue often secure?
- cells in injured/infected tissue often secure molecules that stimulate the release of additional neutrophils from bone marrow
45
What happens during severe infections?
- for severe infection—> number of WBCs in bloodstream may increase a lot within a few hours
46
What does systematic inflammatory response sometimes cause?
- Systematic inflammatory response —> sometimes involves fever
- substances released by macrophages activated by certain pathogens cause body’s thermostat to reset @ higher temperature—> this may enhance phagocytosis + accelerate tissue repair
47
What is septic shock? (2)
- when certain bacterial infections induce overwhelming system inflammatory response
- fatal in 1/3 cases (occurs more in old people)
48
What is crohn’s disease + ulcerative colitis?
- debilitating disorders in which chronic inflammation disrupts intestinal function
49
What does pathogen recognition in mammal trigger?
triggers production + release of peptides(attracts pathogens /impede their reproduction)
50
What are interferons?
Proteins that provide innate defense by inhibiting virus replication —> help activate macrophages. -Interferons (IFNs) are proteins made and released by host cells in response to the presence of pathogens such as viruses, bacteria, parasites or tumor cells.
51
What do inteferons allow?
- Allow for communication between cells to trigger the protective defenses of the immune system that eradicate pathogens or tumors.
52
What are inteferons named after?
- Interferons are named after their ability to “interfere” with viral replication within host cells.
53
- IFNs are divided into three classes:
type I IFN
type II IFN
type III IFN
54
What do IFNs activate?
-IFNs activate immune cells (natural killer cells and macrophages ), increase
recognition of infection and tumor cells by up-regulating antigen presentation
to T lymphocytes—>increase the ability of uninfected host cells to resist new
infection by virus
55
The complement system is made of a variety of proteins that, when inactive, circulate in the blood. When activated, these proteins come together to initiate the complement cascade, which starts the following steps: (4)
1. ) Opsonization: Opsonization is a process in which foreign particles are marked for phagocytosis. All of the pathways require an antigen to signal that there is a threat present. Opsonization tags infected cells and identifies circulating pathogens expressing the same antigens.
2. ) Chemotaxis: Chemotaxis is the attraction and movement of macrophages to a chemical signal. Chemotaxis uses cytokines and chemokines to attract macrophages and neutrophils to the site of infection, ensuring that pathogens in the area will be destroyed. By bringing immune cells to an area with identified pathogens, it improves the likelihood that the threats will be destroyed and the infection will be treated.
3. ) Cell Lysis: Lysis is the breaking down or destruction of the membrane of a cell. The proteins of the complement system puncture the membranes of foreign cells, destroying the integrity of the pathogen. Destroying the membrane of foreign cells or pathogens weakens their ability to proliferate, and helps to stop the spread of infection.
4. ) Agglutination: Agglutination uses antibodies to cluster and bind pathogens together, much like a cowboy rounds up his cattle. By bringing as many pathogens together in the same area, the cells of the immune system can mount an attack and weaken the infection. Other innate immune system cells continue to circulate throughout the body in order to track down any other pathogens that have not been clustered and bound for destruction.
56
How do some some pathogens avoid destruction ?
Because their outer capsule interferes with molecular recognition and phagocytosis
57
Give examples of pathogens that are hard to break down? (2)
* Streptococcus pneumoniae is one such bacterium, a major cause of pneumonia and meningitis in humans
* Mycobacterium tuberculosis, can be recognized by the host but resists breakdown
* This organism causes tuberculosis (TB), a disease that kills more than 1 million people per year
58
Which two types of lymphocytes does adaptive immunity rely on?
T-cells :
↳ lymphocytes that mature in thymus above heart
B-cells:
↳ lymphocytes that mature in the bone marrow
59
What are antigens a trigger for?
Immunity
60
What are antigens?
- Substances that can elicit a response from B/T cell
| - T/B cells bind to antigens via receptors specific to part of one molecule of that pathogen
61
Immune system cells produce millions of different antigen ____.
receptors
62
What are the characteristics of antigens?
—> usually foreign
| —> typically large molecules (proteins/polysaccharides)
63
What is an epitope?
—> small, accessible part of an antigen that binds to an antigen receptor
64
How are individual B&T cells specialised? (2)
- each individual B&T cell —> specialised to recognise a specific type of molecule
- antigen receptors of B&T cells have similar components —> BUT they encounter antigens in different ways
65
What happens when a B cell encounters an antigen?
When a naive B cell encounters an antigen that fits or matches its membrane-bound antibody, it quickly divides in order to become either a memory B cell or an effector B cell, which is also called a plasma cell. Antibodies can bind to antigens directly.
66
What do memory B cells express?
-Memory B cells express the same membrane-bound antibody as the original naive B cell, or the “parent B cell”.
67
What do plasma B cells produce? (3)
- Plasma B cells produce the same antibody as the parent B cell, but they aren’t membrane-bound.
- Instead, plasma B cells can secrete antibodies.
- Secreted antibodies work to identify free pathogens that are circulating throughout the body.
68
What happens when a naive B cell divides and differentiates?
- When the naive B cell divides and differentiates, both plasma cells and memory B cells are made.
- B cells also express a specialized receptor, called the B cell receptor (BCR).
69
What do B cell receptors assist with?
- B cell receptors assist with antigen binding, as well as internalization and processing of the antigen.
- B cell receptors also play an important role in signaling pathways.
70
What happens after the antigen is internalized?
- After the antigen is internalized and processed, the B cell can initiate signalling pathways, such as cytokine release, 7 to communicate with other cells of the immune system
71
What is the role of T cells? (7)
1. Once formed in the bone marrow—>T progenitor cells migrate to the thymus (hence the name “T cell”) to mature and become T cells.
2. While in the thymus—>developing T cells start to express T cell receptors (TCRs) and other receptors called CD4 and CD8 receptors.
3. All T cells express T cell receptors, and either CD4 or CD8, not both.
4. So, some T cells will express CD4, and others will express CD8.
5. Unlike antibodies, which can bind to antigens directly, T cell receptors can only recognize antigens that are bound to certain receptor molecules, called Major Histocompatibility Complex class 1 (MHCI) and class 2 (MHCII).
6. These MHC molecules are membrane-bound surface receptors on antigen-presenting cells, like dendritic cells and macrophages.
7. CD4 and CD8 play a role in T cell recognition and activation by binding to either MHCI or MHCII
72
What is the process that T cell receptors have to undergo?
- T cell receptors have to undergo a process called rearrangement, causing the nearly limitless recombination of a gene that expresses T cell receptors.
- Process of rearrangement allows for a lot of binding diversity—>This diversity could potentially lead to accidental attacks against self cells and molecules because some rearrangement configurations can accidentally mimic a person’s self molecules and proteins.
73
- Mature T cells should recognize only foreign antigens combined with ___-____ molecules in order to mount an appropriate immune response.
self-MHC
74
In order to make sure T cells will perform properly once they have matured and have been
released from the thymus, they undergo two selection processes:
1 -Positive selection (3)
- Positive selection ensures MHC restriction by testing the ability of MHCI and MHCII to distinguish between self and nonself proteins.
- In order to pass the positive selection process, cells must be capable of binding only self-MHC molecules.
- If these cells bind nonself molecules instead of self-MHC molecules, they fail the positive selection process and are eliminated by apoptosis.
75
In order to make sure T cells will perform properly once they have matured and have been
released from the thymus, they undergo two selection processes:
2 - Negative selection: (4)
- Negative selection tests for self-tolerance.
- Negative selection tests the binding capabilities of CD4 and CD8 specifically.
- The ideal example of self-tolerance—> a T cell will only bind to self-MHC molecules presenting a foreign antigen.
- If a T cell binds, via CD4 or CD8–>a self-MHC molecule that isn’t presenting an antigen, or a self-MHC molecule that presents a self-antigen, it will fail negative selection and be eliminated by apoptosis.
76
What would happen with positive selection and negative selection? (2)
- These two selection processes are put into place to protect your own cells and tissues against your own immune response.
- Without these selection processes, autoimmune diseases would be much more common
77
After positive and negative selection, we are left with three types of mature T cells:
- Helper T cells
- Cytotoxic T cells
- T regulatory cells
78
What is the function of Helper T cells?
- Helper T cells express CD4 and help with the activation of Tc cells, B cells, and other immune cells.
79
What is the function of cytotoxic T cells?
- Cytotoxic T cells express CD8, and are responsible for removing pathogens and infected host cells.
80
What is the function of T regulatory cells?
- T regulatory cells express CD4 and another receptor, called CD25. T regulatory cells help distinguish between self and nonself molecules, and by doing so, reduce the risk of autoimmune diseases
81
4 major characteristics to adaptive immune system
1. ) Immense diversity of lymphocytes & receptors
2. ) Self-tolerance—> lack of reactivity against an animal's own molecules + cells
3. ) B & T cells proliferate after activation
4. ) Immunological memory
82
What is the process of proliferation? (7)
1. In the body there are few lymphocytes with antigen receptors specific for any particular epitope
2. In the lymph nodes—>antigen is exposed to a steady stream of lymphocytes until a match is made
3. This binding of a mature lymphocyte to an antigen initiates events that activate the lymphocyte bearing the receptor
4. Once activated—>B or T cell undergoes multiple cell divisions (clonal selection) to produce a clone
of identical cells
5. Some cells from the clone become effector cells that act immediately against the antigen
6. Effector cells are plasma cells that secrete antibodies
7. The remaining cells in the clone become long-lived memory cells that can give rise to effector cells if the same antigen is encountered again
83
What are effector cells?
Plasma cells that secrete anti-bodies.
84
How is adaptive immunity triggered?
Adaptive immunity is triggered when a pathogen evades the innate immune system for long enough to generate a threshold level of an antigen. An antigen is any molecule that induces an immune response, such as a toxin or molecular component of a pathogen cell membrane, and is unique to each species of pathogen.
85
A typical adaptive immune response includes several steps: (6)
1. ) The antigen for the pathogen is taken up by an antigen-presenting cell (APC), such as a dendritic cell or macrophage, through phagocytosis.
2. ) The APC travels to a part of the body that contains immature T and B cells, such as a lymph node.
3. ) The antigen is processed by the APC and bound to MHC class II receptors and MHC class I receptors on the cell membrane of the APC.
4. ) The antigen is presented to immature helper T cells and cytotoxic T cells through binding the MHC II (helper T) or MHC I (cytotoxic T) to T-cell receptors.
5. ) These T lymphocytes mature and proliferate. Helper T cells activate B cells, which proliferate and produce antibodies specific to the antigen, while cytotoxic T cells destroy pathogens that bear the antigen that was presented to them by the APCs.
6. ) Memory B and T cells are formed after the infection ends.
86
What is immunological memory responsible for?
- responsible for long-term protections against diseases.
87
What is the primary immune response?
~ Primary immune response—> first exposure to specific antigen—> clone of
lymphocytes—> formed that are specific to the pathogen
88
What is the secondary immune response?
~ Secondary immune response—> memory cells facilitate a faster, greater and
more prolonged response from a reservoir of T&B memory cells.
89
Adaptive immunity defends against infection of body fluids and body cells
• The defenses provided by B and T lymphocytes can be divided into the ______ immune response and the _____-_____ immune response.
humoral
| cell-mediated
90
What is the humoral immune response?
In the humoral immune response, antibodies help neutralize or eliminate toxins and pathogens in the blood and lymph.
91
What is the cell-mediated response?
In the cell-mediated immune response, specialised T cells destroy infected host cells.
92
What type of T cell activates both the humoral and cell-mediated
immune responses?
• This requires the presence of a foreign molecule that can bind the antigen receptor on the helper T cell and, the antigen must be displayed on the surface of an antigen-presenting cell.
93
Describe the process of how T cells activate adaptive immunity? (4)
* Antigen-presenting cells have class I and II MHC molecules on their surfaces
* Class II MHC molecules provide a molecular signature by which antigen presenting cells are recognised
* Antigen receptors on the surface of helper T cells bind to the antigen and the class II MHC molecule; then cytokine signals are exchanged between the two cells
* The helper T cell is stimulated to produce its own set of cytokines
94
How is the helper T cell activated by a dendritic cell? (9)
1. In the tissue fluid, cells of the second line of innate defense such as dendritic cells carry out
surveillance for any foreign objects
2. Dendritic cells engulf the virus/foreign body with an endosome—> fuses with a lysosome whose
enzymes digest the virus
3. resulting fragments of virus after digestion —>epitopes
4. dendritic cell then attaches to virus epitopes to presentation molecules called —> MCH II
5. this complex fold outwards so that it sits on outside of dendritic cell membrane
6. dendritic cell then enters a lymphatic vessel— >travels to nearby lymph node—> debtritic cell part of innate immune defenses & counters a helper T cell which is part of adaptive defenses
7. The T cell receptor—> TCR of this helper T cell recognises the virus epitope
8. while the CD4 glycoprotein associated with TCR recognises the MCH II
9. dendritic cell then stimulates activation of this helper T cell
95
Describe the entire process of humoral immune response.
1. Antibodies help neutralize/eliminate toxins and pathogens in the blood + lymph
2. Characterised by the secretion or antibodies by clonally selected B cells
3. Begins with B cell activation
4. B cell activation involves helper T cells & proteins on the surface of the pathogens
5. When an antigen binds a B cell, the cell takes in a few foreign molecules by receptor mediated endocytosis
6. The class II MHC protein of the B cell then presents an antigen fragment to a helper T cell, a process that is critical to B cell activation
96
An activated B cell gives rise to thousands of identical plasma cells
• These begin producing and secreting ______.
• Most antigens recognized by B cells contain multiple ______.
• A variety of B cells activated by one antigen will give rise to _____ cells producing antibodies directed against different epitopes of the common antigen
antibodies
epitopes
plasma
97
What is the role of B cells in humoral immunity? (5)
- deals with invaders in body fluids
- B cells are lymphocytes that send out antibody molecules in response to certain stimuli
- many kinds of B cells—> each kind produces and presents its own uniquely shaped antibody receptors in its plasma membrane
- these unique receptors only bind to antigens with specific shapes
- the B cell that successfully binds to an antigen is stimulated to proliferate into a clone of cells with the same specificity
98
antigen selected proliferation is known as —> _____ _____.
clonal selection
99
What does B cell proliferation produce?
- B cell proliferation produces clones of plasma cells and memory cells.
100
What are memory cells and what do they account for?
- Memory cells are long-lived cells that can respond rapidly to future exposures to the same antigen
- they account for the speed and strength of the secondary immune response that gives us long-term immunity to a disease
101
How fast do plasma cells multiply?
- Plasma cells multiply rapidly —> produce and secrete antibodies in increasing amounts , peaking about 2 weeks after the activation of the original B cell
- These antibodies flow through the body’s fluids and tag the original foreign antigen molecule —> marking them for destruction
102
How do cytotoxic t cells use toxic proteins to kill cells infected by viruses or other intracellular pathogens?
- Cytotoxic T cells recognise fragments of foreign proteins produced by infected cells
- The activated cytotoxic T cell secretes proteins that disrupt the membranes of target cells and trigger apoptosis (cell death)
103
Cytotoxic T cells express ____ , and are responsible for removing pathogens and infected host cells.
CD8
104
Which cells are the main warriors of cell-mediated immunity?
- cytotoxic T cells are the main warriors of cell-mediated immunity —> which attacks body cells that have been altered by infection or cancer or transplanted cells that are foreign to the body
105
What do infected, cancerous, or transplanted cells display?
- An infected, cancerous, or transplanted cell displays foreign antigens on its surface
106
What do T cell receptors do and how Cytotoxic T cells respond?
-T cell receptors on specific cytotoxic T cells recognise and bind to specific antigens on cells
- Cytotoxic T cells respond to this contact and to interleukin-2 sent out by helper T cells —> by
producing the protein Perforin
107
Where are perfornin molecules released and where do they attack?
- Perforin molecules are released from the cytotoxic T cell and attack the membrane of the infected cell
—> punching holes in it which allows water and solutes to enter
- The cell burst and is killed —> this way cytotoxic T cells deprive pathogens of their host cells so they
cannot reproduce
108
How are tumor cells removed?
- Tumor cells also removed from the body by cytotoxic T cells —> this way cell mediated immunity is carried out by cytotoxic T cells
109
How does HIV operate?
HIV finds the white blood cells, called CD4 cells. HIV gets inside the CD4 cell and makes copies of itself. Then, HIV kills the CD4 cell and the new HIV copies find other CD4 cells to get inside and start the cycle again. HIV kills immune system cells that help the body fight infections and diseases.
