Overview of Immune Responses Flashcards
(109 cards)
0
Q
What is the immune system comprised of?
A
Cells and molecules which collectively mediate an immune response
1
Q
What is immunity?
A
It is a defense mechanism that provides protection from infectious diseases
2
Q
What can also elicit an immune response?
A
Noninfectious foreign substances called antigens (Ags)
3
Q
What can cause collateral damage?
A
An immune response against microbes can cause tissue injury (immunopathology)
4
Q
What happens if immune system goes against self Ags?
A
autoimmune response
5
Q
What are antigens?
A
Substances which induce an immune response
6
Q
What are types of antigens?
A
Proteins, carbs, lipids, nucleic acids
7
Q
What do microbes have that can be recognized by the immune system?
A
many different antigens
8
Q
What can antigens contain a number of?
A
Different antigenic determinants to which individual antibodies or T cell responses are made
9
Q
What is the smallest unit of antigenic determinant to which an antibody can be made?
A
About three to six amino acids or five to six sugar residues long
10
Q
What are all large molecules?
A
Multideterminant-have multiple epitopes
11
Q
What do antibodies bind to?
A
Conformational antigenic determinants which depend on folding of the molecule
12
Q
What do T cell receptors recognize?
A
Linear amino acid sequences
13
Q
What are Ags that can stimulate an immune response called?
A
Immunogens
14
Q
All Immunogens are antigens but _______
A
Not all antigens are immunogens
15
Q
What can bind to Ab’s or TCR’s but they cannot initiate an immune response?
A
Haptens
16
Q
What is the first line of defense against infection?
A
Innate immune system
17
Q
How does the innate immune system work?
A
Works rapidly, gives rise to the acute inflammatory response, and has some specificity for microbes, but NO memory
18
Q
What takes longer to develop, is highly specific, remembers what microbe it has encountered previously (memory)?
A
Adaptive immune system
19
Q
What exists even before infection and are poised to respond rapidly to infections?
A
Innate immunity
20
Q
What are other names for innate immunity?
A
Natural or native immunity
21
Q
What does native immunity react to?
A
products of microbes and injured cells
22
Q
How does native immunity respond to repeated exposures?
A
In the same way everytime
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Q
What does native immunity recognize?
A
Recognizes common antigens belonging to groups of related microbes
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What does native immunity not distinguish?
Fine differences between microbes
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What are principal components of innate immunity?
Physical and chemical barriers (skin, mucosal epit, antimicrobial molec)
Phagocytic cells (neutrophils, macrophages), dendritic cells, and natural killer cells and other innate lymphoid cells
Blood proteins, including the complement system and other mediators of inflammation
26
What are the components of adaptive immunity?
Cellular and chemical barriers - lymphocytes, antibodies at epithelial surfaces
Blood proteins - antibodies, cytokines
Cells - B and T lymphocytes
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In addition to inflammation, the innate immune system is also called what?
"decision-making stage" of an immune response
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Before providing instructions to adaptive immunity, what does the innate immunity evaluate?
It evaluates the invader in the context of intracellular vs extracellular microbes and then passes on the info
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How do cells communicate?
Direct cell-to-cell contact and interactions involving cytokines and chmokines
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What are cytokines?
Large group of small secreted proteins with diverse structures and functions, which regulate and coordinate many activities of the cells of innate and adaptive immunity
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What does each cell express for several cytokines?
A set of specific signaling receptors
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What are the functions of cytokines?
Growth and differentiation of all immune cells, activation of effector function of lymphocytes and phagocytes
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What are chemokines?
Large subset of structurally related cytokines that regulate cell migration and movement
34
What are the two major types of lymphocytes?
B and T cells
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What are critical to the development of specific immunity?
Interactions between T and B cells as well as between T cells and APCs
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Where do T cells mature? What doe they give rise to?
Under the influence of the thymus. On stimulation by Ag, they give rise to cellular immunity
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Where do B cells mature? What do they give rise to?
Be cells mature mainly under the influence of bone marrow and give rise to humoral immunity.
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What are soluble molecules in the immune system
Immunoglobulins
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Who is the father of humoral immunity?
Paul Ehrlich
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What did Paul Ehrlich do?
Postulated that immune cells use receptors
Coined the term antibodies
Model for the function of B cells
Humoral theory of immunity
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What is humoral adaptive immunity?
Immunity mediated by antibodies (Abs) in the blood and mucosal secretions which are produced by cells called B lymphocytes
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What do Antidbodies do?
Recognize microbial antigens, neutralize the infectivity of the microbes, and target microbes for elimination by various effector mechanisms.
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What is the principal defense mechanism against extracellular microbes?
Humoral adaptive immunity because of antibodies
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Who is the father of cell-mediated immunity?
Elie Metchnikoff
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What did Elie Metchnikoff discover?
Stated that host cells are the principal mediators of immunity
Phagocytes
Nobel prize 1908
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When did the cellular theory of immunity become firmly re-established?
When resistance could be transferred with cells but not with serum
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What is the specificity of cell-mediated immunity due to?
T cells which often function with phagocytes to eliminate microbes
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What does cell-mediated immunity defend against?
Intracellular microbes such as viruses and some bacteria where they are inaccessible to circulating antibodies
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What is the function of cell-mediated immunity?
Destruction of microbes residing in phagocytes or the killing of infected cells to eliminate reservoirs of infection
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What contributes to eradication of extracellular microbes by helping B cells make effective antibodies?
T helper cells
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What activates macrophages to kill phagocytized microbes?
T helper cells
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What directly destroys infected cells?
Cytotoxic T cells
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What happens when an Ag is introduced into an individual?
Lymphocytes with receptors for this Ag seek out and bind it and are triggered to proliferate and differentiate, giving rise to clones of cells specific for the Ag
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What is the clonal selection hypothesis?
Explains how the immune system could respond to a large number and variety of Ags
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Who came up with the clonal selection hypothesis?
Suggested by Dr. Jerne and further by Dr. Burnet
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According to the clonal hypothesis, when do Ag-specific clones develop?
Before and independent of exposure to Ag
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What is a clone?
Lymphocyte of one specificity and its progeny
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What is a characteristic of the immune system involving clones?
A very large number of clones is generated during the maturation of lymphocytes, thus maximizing the potential for recognizing diverse microbes
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What happens once an Ag selects a preexisting clone of specific lymphocyte? What does the same principle also apply to?
Proliferation and differentiation of that clone is stimulated. Also applies to T lymphocytes
60
Compared to the primary adaptive immune response, how fast is the secondary response to the same antigen?
Secondary is more rapid and larger than the primary response because of memory
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What happens during contraction phase?
Expanded lymphocyte clones die and homeostasis is restored. A few become memory cells
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What are more effective in combating microbes than naive lymphocytes?
Memory cells because they are more numerous than naive cells specific for the Ag and respond faster and more effectively than do naive cells
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What is an important goal of vaccination?
Generation of memory cells
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Who is the father of immunology?
Dr. Pasteur who developed the principle of vaccination and contributed to the foundation of immunology
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The concept of protective immunity dated back to when?
Ancient Chinese custom of making children resistant to smallpox by having them inhale powders made from skin lesions of patients recovering from the disease. Edward Jenner later successfully vaccinated against smallpox
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What is active immunity?
Conferred by a host response to a microbe or microbial Ags
(vaccine or infection)
Goal is to create lymphocytes with specificity and memory to pathogen
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What is passive immunity?
Conferred by adoptive transfer of antibodies or T lymphocytes specific for the microbe.
Provides resistance to infection and are specific for microbial Ags but no memory.
Example-mothers immunity passed onto child but does not remain
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Role of B lymphocytes:
Recognize soluble Ags and develop into Ab-secreting cells
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Role of T helper cells
Recognize ags on the surfaces of Ag presenting cells and secrete cytokines, which stimulate different mechanisms of immunity and inflammation
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Role of cytotoxic T cells
Recognize Ags on infected cells and kill these cells
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Role of regulatory T cells:
Suppress and prevent immune responses to self antigens for example
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What is the primary function of phagocytes
To ingest and destroy microbes and get rid of damaged tissues
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What are types of phagocytes?
Neutrophils and macrophages
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What are the steps of functional responses of phagocytes?
1. Recruitment of cells to the sites of infection
2. Recognition of and activation by microbes
3. Ingestion of the microbes by the process of phagocytosis
4. Destruction of ingested microbes
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What do activated phagocytes secret?
Cytokines to promote or regulate immune responses
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What are neutrophils also called?
Polymorphonuclear leukocytes because their nucleus is segmented into three to five connected lobules
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What are the most abundant population of circulating white blood cells that are 12 to 15 um in diameter?
Neutrophils
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What mediates the earliest phases of inflammatory reactions?
Neutrophils
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Where are neutrophils produced and where do they arise from?
In the bone marrow. They arise from precursors that also give rise to mononuclear phagocytes
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What is the production of neutrophils stimulated by?
Cytokine called granulocyte colony-stimulating factor
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How many neutrophils are produced a day in an adult?
10^11
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How long do neutrophils circulate in the blood?
Four hours or a few days
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After entering tissues, how long do neutrophils function?
for 1 to 2 days and then they die
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How are specific granules in neutrophils stained?
With neutral dyes (neutrophiles) but not with eosin or basic dyes
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What are azurophilic granules?
Lysosomes that contain enzymes and other microbicidal substances. (Elastase, myeloperoxidase, cathepsin, acid hydrolases) Found in neutrophils
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How do neutrophils respond to microbes of small sizes?
Bind and internalize the cells via phagocytosis. The microbes are sequestered in phagosomes that fuse with asurophilic granuels. The production of ROS and the release of enzymes (i.e elastase) into the phagosome contribute to killing the microbes
87
How do neutrophils respond to microbes that are large?
Cannot internalize them, so azurophilic granules are free to deliver their contents into the nucleus instead, which triggers chromatin decondensation and the release of NETs. NETs contribute to the immobilization and killing of extracellular microbes, but at the cost of some tissue damage
88
Describe the formation of NET
It is a rapid, active process occurring in minutes that has been suggested to be mediated by a cell death-dependent process referred to as NETosis.
89
What is NET?
NETs are composed of DNA and histones and are decorated by proteins from primary granules and secondary granules
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In addition to the nucleus, what can also serve as a source of DNA for NET formation?
Mitochondria
91
Mast cells, basophils, and eosinophils play roles in what type of immunity?
Innate and adaptive immunity responses
92
What protects against helminths and reactions that cause allergic diseases?
Mast cells, basophils, and eosinophils
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What common feature do Mast cells, basophils and eosinophils share?
Cytoplasmic granules filled with various inflammatory and antimicrobial mediators
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What are cytoplasmic granules in mast cells filled with? What are they stained with?
Histamine and other mediators. Stained purple with giemsa
95
What shows the characteristic blue granules stained with Giemsa?
Blood basophil
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What contains basic proteins which are stained red with acidic dye eosin?
Eosinophil granules
97
What are common sites of mast cells?
Sites that are exposed to the external environment such as the skin
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What are mast cells found in close proximity to?
Blood vessels, where they can regulate vascular premeability and effector-cell recruitment
99
How do mast cells communicate?
Although they do not have direct cell to cell contact with local cell populations, they can modulate the behavior of these and other neighboring effector cells through the release of mediators
100
What are the two types of mononuclear phagocytes?
Circulating monocytes and resident tissue macrophages
101
What are many tissues populated with?
Long-lived resident macrophages witch assume specialized phenotypes depending on the organ
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What is the lineage of macrophages?
Arise from committed precursor cells in the bone marrow, driven by monocyte/macrophage colony stimulating factor
Mature monocytes enter the blood circulation and then migrate into tissues, where they further mature into macrophages, especially during inflammation
103
What are the special types of macrophages the differentiate from the fetus and yolk sac?
Microglial cells: brain
Kuppfer cells: liver
Alveolar macrophage: lung
Sinusoidal macrophages: spleen
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What process is important for the eradication of microbes that are ingested by the phagocytes but resist killing?
Microphages present Ags to helper T cells at the sites of infection that leads to T cell activation and production of cytokines that further activate the microphages
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What do dendritic cells arise from?
A common precursor cell of the myeloid lineage in the bone marrow.
106
What do dendritic cells further differentiate into?
Subsets, the major ones being classical DCs and plasmacytoid DCs
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What do inflammatory DCs arise from?
Monocytes in inflamed tissues
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Where are Langerhans cells located and where do they develop from?
In the skin and appears early in life and may develop from embryonic precursors
