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87 Cards in this Set
- Front
- Back
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What does the immune system defend against?
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Viruses: nonliving, not cellular, NA with ptn coat
Bacteria: non-nucleated, single cell microorganism Parasites: multicellular worms and protozoans |
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What kind of system is the immune system?
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Dynamic and integrated network
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What 2 categories can protection by the immune system be divided into?
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1) Recognition
2) Response |
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Describe recognition
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Immune system can distinguish between self and nonself
Can recognize molecular patterns that characterize and rapidly deal with gps of pathogens Can detect subtle chemical differences between pathogens |
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Describe the immune response
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Immune recognition triggers an effector response that elimiates/neutralizes the invader
-> Get a variety of effector fcts suited to the disposal of the particular pathogen |
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How can the I.S. distinguish btw self and nonself?
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The body's cells have unique markers (MHC)
MHC identifies the cell as self |
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What is self tolerance?
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Ability of the I.S to attack abnormal or foreign cells but spare our own normal cells
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What are non-self markers?
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Molcules o the surface of foreign or abormal cells or particles that act as flags to the immune system as "nonself" (like for graft rejection)
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What is MHC?
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Set of genes that encode for Ag presenting ptns
Class I and II They present different peptides from self/nonself Ag |
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Where is MHC I?
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On every nucleated cell in the body (.: not on RBCs)
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Which cells rec'z MHC I?
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NK cells
CD8 T cells (CTL) |
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Which cells express MHC II?
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on professional APCs
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Which cells recognize MHC II?
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CD4 (Th cells)
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What is the role of MHC ptns?
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Bind small pepties and preset them at the cell surface for the inspection of the TCR
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Describe the innate immune system
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First line of defense
Prevents most infections or eliminates them within a few hours Recognition elements of this system distinguish self and pathogens It is not specialized to distinguish small differences in foreign molecules Nonspecific host defeces that exist before infection |
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What are the mechanisms of innate immunity?
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1) Anatomic
2) Physiologic 3) Endocytotic} 4) Phagocytic} 5) Inflammatory |
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How does adaptive immunity develop?
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In response to infection
Adapts to recognize, eliminate and remember foreign elements ->Adaptive immunity depends on innate immunity and begins a few days after the initial infection |
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What is adaptive immunity?
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The comprehensive second line of defence that eliminates pathoges that evade the innate system or persist anyways
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Which cells mediate the adaptive immune response?
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Lymphocytes:
B and T cells |
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Are the innate and adaptive I.S.'s independent of each other?
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No
Highly interactive and cooperative system Produces a combined response that is much more effective than a singular response |
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What characterizes the adaptive immune system?
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Adaptive has:
Antigenic specificity Diversity Memory* (unlike innate) Self/nonself recognition |
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What does memory ensure?
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If infected with same pathogen a second, adaptive immune response will be faster the second time (innate response will stay the same)
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Compare innate and adaptive:
Response time |
I: hours
A: days |
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Compare innate and adaptive:
Specificity |
I: limited and fixed
A: highly diverse, improves during course of immune response |
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Compare innate and adaptive:
Response to repeat infection |
I:identical to primary response
A: much more rapid that primary response |
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Compare innate and adaptive:
Major components |
I: Barrier (skin), phagocytes, pattern recognition molecules
A: Lymphocytes, Ag-specific receptors, Ab |
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Compare innate and adaptive:
Diversity |
I: Limited number of germline enoded receptors
A: Highly diverse, large number of receptors from genetic recombination (TCR/Ig) |
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Compare innate and adaptive:
Memory responses |
I: None
A: Persistent memory, with faster responses on susequent infection |
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Compare innate and adaptive:
Self/non-self discrimination |
I: Perfect, no microbe-specific patters in host
A: very good, but can have a failure of self/nonself discrimination that results in autoimmune disease |
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Compare innate and adaptive:
Soluble components of blood or tissue fluids |
I: many microbial peptides/ptns
A: Ab |
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How are subsets of lymphocytes defined?
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By cluster desigation (D) surface markers that the cells carry (ex: CD4, CD8)
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What are the Ag receptors of adaptive immunity?
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-Ab, secreted or BCR
-TCR |
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What is the link between innate and adaptive immunity?
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professional APCs
--> Especially DCs |
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Describe the progression of DCs.
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-Immature DCs live in the peripheral tissue
-DCs migrate to the regional lymph node via the lymphatic system -Mature DCs activate naive T-cells in lymphoid organs such as lymph nodes |
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Describe lymphocyte dev'l.
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Lymphocytes form in the bone marrow
Stem cells follow 2 paths to become B or T cells B cells differentiate and mature in the BM, then the spleen, where they spend the Ag-dependent part of their dev'l |
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Where do the T-cells dev'p?
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Thymus glad process T cells that come from the BM
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Where do B and T cells circulate?
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lymph nodes and spleen
-> lymphocytes are densest where they devlope: BM, thymus gland, lymph nodes and spleen |
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How do B cells dev'p?
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Pre-B cells dev'p by the first few months of life in the BM
2nd stage takes place in the spleen: activation of naive B cell after it binds a specific Ag |
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How do B cells defend the body?
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Produce Abs that attack the pathogen (doesn't directly attack the pathogen itself)
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What happens whe a B cell sees an Ag?
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Differentiates into a plasma cell
Plasma cell produces Ab molecules that can combine with a specific kind of Ag All Ab eventually enter the blood, lymph or secretions |
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What are Ab?
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Ptns (immunoglobulins) that are secreted by activated B cells
2 heavy and 2 light chains Each molec has 2 Ag binding sites and one complement or FcR binding site |
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What are the AB subclasses?
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IgM
IgG IgE IgA IgD |
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What does IgM do?
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Ab that naive B cells synthesize and insert into their own plasma mb
Predominant class produced after initial contact with an antigen |
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What is IgG?
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most abundant Ab
produced in large amts |
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What is IgE?
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Protects vs parasitic worms with Th2
Ab mediator for common allergic responses |
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What is IgA?
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Found in secretions of digestive, respiratory and genitourinary systems
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What is IgD?
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On the surface of many B cells
fct: involved in antimicrobial mechanism with basophils |
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What are the 3 ways in which Ab can participate in host defense?
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1) Neutralization
2) Opsonization 3) Complement activation |
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What is neutralization?
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Bacterial toxins are neutralized by Abs so that they can't attach to anything and are then ingested by macrophages
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What is opsonization?
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The bacterial toxin is completely covered with Ab and is then ingested by macrophages
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What is complement activation?
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Bacteria in plasma are surrouded by Ab which activate complement which causes lysis ad ingestion of the bacteria
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What is the B cell primary response?
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Initial encouter with a specific Ag and release of specific Ab that reaches its peak in a few days
Formation of B memory cells |
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What is the B cell secondary response?
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Later encouter with the same Ag triggeres a much quicker response
B memory cells rapidly divide, making more plasma cells ad Abs |
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Why are the vaccines generated based o B cells and not T cells?
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We don't have required control of intracellular region
Hard to generate intracellular vaccines because we don't know what's going on |
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Describe immunization.
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Active immunity can be established by vaccination
Inject patient with attenuated/dead form of the pathogen adjuvant |
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What is the point of immunization?
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Triggers formation of Ab ad memory B cells
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Why are booster shots required?
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To keep the Ab titer high/inc titerss
After secondary vaccine, have much higher titer of Ab compared to after the initial vaccination |
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What are the 2 main populations of T cells?
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CD4+
CD8+ |
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What happens to developing T cells in the thymus?
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get both CD4+ and CD8+
-> double positive cells ->eventually lose one of these to just be just CD4+ or CD8+ |
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What are CD4+ cells?
CD8+? |
CD4+: Th-cells
CD8+: Cyt T-cells |
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What do T cells do?
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directly attack a pathogen
-> Cell mediated immunity |
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What are the effector molec of CD8+ cells?
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Perforin
Grazyme Granulysin Fas ligands (also: IFN-y, LT-a, TNF-a) |
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What do Th1 cells activate?
With what molec? |
Macrophages
IFN-y GM-CSF TNF-a CD40L Fas ligad (also: IL3,LT-a, CXCL2) Important inflammatory response CD40 regularly produces cytokines |
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What do Th2 cells activate? Effectors?
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B-cells
IL-4/5/13 CD ligand (also: IL-2/10. G-CSF, TGF-CCL11, CCL17/TARC) |
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What is Th17 for?
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inflammatory reponse
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What does Th17 do?
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neutrophil recruitment
IL-17a/R-17f IL-6 (also: TNFa, CXL1, GROa) |
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What do Treg cells do?
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expresss anti-inflam cytokines
IL-10 TGF-b (Also:GM-SF) |
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Describe T cell activation
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naive T cell activated when an APC binds to its receptor:TCR
->this causes it to rapidly divide into clones of the same T cells -the cells of these clones differentiate into effector ad memory cells |
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What are the 2 signals required for T cell activation?
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signal 1: Interaction btw TCR amd MHC
signal 2: costimulatory signal btw CD28 (on T cell) and B7 (on APC) |
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How are CD4+ cells activated? (Th cells)
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Cell activation initiate by interaction of TCR-CD3 with Ag-MHC II on the surface of APC
This starts a cascade of events in the T cell that results in the growth and prolif of the T cell This is due to inc of IL-2 secretion by the T-cells ad inc of IL-2 receptors on the T cell surface |
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What is IL-2?
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Potent T cell growth cytokine
Works in an autocrine manner to promote growth, prolif and diff of the T ell |
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What happens if there is no Ag & .: no Ag-MHC II interaction with the TCR?
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If only co-stimulatory signal, there is no response
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What happens if there is no costimulation? (only Ag-MHC II interaction with TCR)
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No activation
T cell becomes unresponsive (anergic) |
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What happens if there is Ag-MHC II interaction with the TCR and a costimulatory signal?
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Get T ell activation
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What is the main role of CD8+ T cells (CTLs)?
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Kill cells
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What is required on cells so that they aren't killed by CTLs?
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MHC I
->Tc cel rec'z and destroys self cells that have been altered or infected |
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How is Tc cell activated?
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1) TCR on CD8+ has to interact with an antigen-MHC I on the surface of a target cell
2) CD8+ T cell must be stimulated by cytokines (especially IL-2) |
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What suppliesTc cells with IL2?
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Activated Th cells
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Describe cell death by CD8+ T cells?
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CTL rec'z ad binds virus infected cells
CTL programs target for death, induing DNA fragmentation CTL migrates to new target Target cell dies by apoptosis |
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How does a Tc cell kill a tumour cell?
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1) Adheres to the cell
2)releases perforin, which forms ringlike holes in the tumour cell's mb and granzymes pass through these rings to trigger apoptosis |
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What do Tc cells release? Why?
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Lymphotoxins perforin and granzyme to kill cells
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What do Th cells do?
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Regulate the fct of B cells, T cells, phagocytes and other leukocytes
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What do suppresor T cells do?
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They are regulatory T cells that suppress lymphocyte fct, .: regulating immunity and promoting self tolerance
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What kind of immuity do T cells help produce?
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Cell mediated immunity
(and adaptive immunity in general) |
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What kind of immunity are B cells involved in?
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Ab-mediated (humoral) immunity
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What are the stages of adaptive immunity?
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-Recognition of Ag
-Activation of lymphocytes -Effector phase (immune attack) -Decline of Ag causes lymphocyte death (homeostatic balance) -Memory cells remain for later response if needed |
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Why is homeostatic balance required?
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If not controlled, you could die of an inflamatory response rather than an infection
Need to be able to turn off the system as well |
