Immunology Flashcards
1
Q
What is the main function of the body defense system?
A
To combat and remove foreign cells, infectious agents, and cancerous cells
2
Q
What are examples of threats targeted by the body defense system?
A
Viruses, bacteria, fungi, parasites, toxins, and cancerous cells
3
Q
What is the main cellular component of the immune response?
A
Leukocytes (white blood cells)
4
Q
What is the general function of white blood cells (WBCs)?
A
To provide rapid and potent defense against infectious agents
5
Q
What is the normal WBC count in adults?
A
Approximately 7000/μL
6
Q
What can foreign cells and infectious agents do to the host?
A
Cause pathological damage and eventually kill their host if they are allowed to multiply unchecked
7
Q
Where are blood cells derived from?
A
Either myeloid stem cell derived or lymphoid stem cell derived
8
Q
3 types of blood cells
A
Erythrocytes (red blood cells), platelets (megakaryocytes), and leukocytes (white blood cells)
9
Q
Types of leukocytes
A
Neutrophils, eosinophils, basophils, monocytes, plasma cells & B cells, T lymphocytes, and NK cells
10
Q
What is the function of leukocytes (WBCs)?
A
To provide rapid and potent defense against infectious agents and foreign cells
11
Q
What is diapedesis?
A
The process by which WBCs deform and pass through small pores in blood vessel walls to reach tissues
12
Q
What molecules mediate diapedesis?
A
Selectins on the endothelial cells of veins (their ligands)
13
Q
How long do granulocytes stay in the blood and tissues?
A
4–8 hours in blood, 4–5 days in tissue
14
Q
What happens to monocytes after entering tissues?
A
They enlarge (5x) and become macrophages that can live for months
15
Q
What is the life span of lymphocytes?
A
Months to years, depending on the body’s needs
16
Q
How do lymphocytes circulate in the body?
A
Continuously between blood, lymphatic system, and tissues
17
Q
Which leukocyte is the most abundant and first to respond to infection?
A
Neutrophils
18
Q
How do neutrophils neutralize bacteria and fungi?
A
By phagocytosis
19
Q
What triggers eosinophil mobilization?
A
Parasitic infections like schistosomiasis and Trichinella
20
Q
How do eosinophils attack parasites?
A
By releasing hydrolytic enzymes and H₂O₂
21
Q
What only mast cells produce in the blood?
A
Produce heparin to prevent coagulation and help fat removal
22
Q
What substances do basophils and mast cells release?
A
Histamine, bradykinin, and serotonin
23
Q
What immune response are basophils and mast cells involved in?
A
Allergic reactions mediated by IgE, they also release histamine and small quantities of bradykinin and serotonin
24
Q
What are neutrophils, eosinophils and basophils also known as?
A
Polymorphonuclear cells or granulocytes
25
Where are the granulocytes and monocytes (and erythrocytes and leukocytes) derived from?
Myeloid stem cells
26
Where are plasma cells, B cells, T lymphocytes, and NK cells derived from?
Lymphoid stem cell derived
27
What is the cellular component in immune response?
Leukocytes (white blood cells)
28
How can WBC count be used as a diagnostic tool to tell if there is infection present?
Increased WBC count
29
Where do WBC enter blood circulation from?
Bone marrow or lymphoid tissue
30
How do WBC know where site of infection is?
Chemotaxis - chemical messenger tells them where it is via attraction
31
Movement of WBC from blood circulation to tissues occurs by
Diapedesis - involves deformation of cells to pass through a small pore
32
What is the small pore in diapedesis mediated by?
Selectins
33
What are the two functional forms of immunity?
1) Innate immune system (first line of defense)
2) Adaptive (acquired) immune system (improves with repeated infections and is specific to the pathogen)
34
Which granulocyte is mobilized following parasitic infection?
Eosinophils
35
Examples of parasitic infection
Schistosomiasis and Trichinella "pork worm"
36
Strongest oxidizing agent in the body (released by eosinophils)
Hydrogen peroxide - breaks up bonds and detoxifies parasites and toxins
37
What does bradykinin do?
Activates pain pathway (e.g. bee sting)
38
What does histamine do?
Increase permeability of the cell, disrupts starling forces by increasing pore size so proteins can now move across membrane
39
What activates and attracts phagocytic cells during the detection of infectious agents?
The presence of infectious agents or compounds from damaged cells
40
Which cells are attracted by chemotaxis in response to infection?
Neutrophils and macrophages
41
What are five factors that cause chemotaxis of phagocytic cells?
1. Some bacterial toxins
2. Degenerative products of inflamed cells
3. Complement complex
4. Cytokines from host or invading cells
5. Foreign membrane proteins triggering leukocytes
42
What is phagocytosis and which cells perform it?
Phagocytosis is the ingestion of microbes or particles; neutrophils and macrophages perform it.
43
Where are selectins and their ligands located?
On the surface of leukocytes and endothelial cells of venous capillaries
44
What triggers the activation of selectins and their ligands?
Chemotactic factors
45
What is the effect of selectins and their ligands on leukocytes?
They slow down leukocytes and they make them sticky so they start rolling, which leads to diapedesis (searches for points to leave blood vessels to adjacent tissue)
46
Which components form the Innate (or natural) immunity?
- Physical barriers and factors
- The soluble compounds
- Cellular component
47
What is the primary physical barrier of the innate immune system?
Intact skin, which most infectious agents cannot penetrate
48
Why are burns or cuts significant in infection risk?
They compromise the physical barrier of the skin, allowing pathogens to enter
49
Name three physiological factors that limit microbial growth
pH, temperature, and oxygen tension
50
Where are pathogens typically introduced into the body?
Through epithelial surfaces of the nasopharynx, gut, lungs, and genito-urinary tract
51
Which ones are the soluble compounds involved in the innate immune system?
- Lysozyme
- The complement complex system
- C- reactive protein
- Cytokines
52
What does lysozyme do?
Enzymes that can attack bacterial cell wall (made of proteoglycan - splits the bond between N-acetylglucosamine and N-acetylmuramic acid
53
What is the complement system composed of?
A set of about 20 serum proteins that interact in a cascade
54
C-Reactive protein
- Bind to surface of damaged cells and bacteria, promote the binding and activation of complement system
- Facilitate opsonization and recognition of bacteria leading to more efficient uptake by phagocytes
55
What are the three complement activation pathways?
1. Classical pathway (antibody-antigen complexes)
2. Alternative pathway (binding to pathogen surfaces)
3. Mannose-binding lectin pathway
56
What enzyme do all complement pathways activate?
C3 Convertase which activates the cascade
57
How is the classical pathway activated?
Antibody-antigen complexes
58
How is the alternative pathway activated?
Binding of complements to surface molecules of pathogens (don't require antibodies)
59
What is the role of C-reactive protein?
Binds to damaged cells and bacteria, activates the complement system, and promotes opsonization
60
What is opsonization?
The process where antibodies tag bacteria to signal leukocytes for phagocytosis
61
Cytokines
Biochemical messengers stimulate leukocyte activity following infection, increase production of granulocytes, monocytes, and lymphocytes
62
Hematopoeisis
Blood cell production
63
Which 2 cytokines are pro-inflammatory, stimulate immune response, and increase hematopoeisis?
Interleukin-1 (IL-1) and Tumor necrosis factor (TNF)
64
What are the functions of IL-1?
Increases hematopoiesis and has proinflammatory effects
65
What do IL-1 and TNF do?
Stimulate the immune system and promote inflammation
66
What are the cellular components which make up the innate immune system?
NK cells and phagocytic cells
67
What do NK cells recognize?
Surface changes on virally infected cells, foreign cells, and some tumor cells
68
What do NK cells do after recognizing abnormal cells?
Bind to and kill them
69
What activates NK cells?
Interferons produced by virally infected cells or lymphocytes
70
Do NK cells have immunological memory?
No, they do not
71
Natural killer cells are lymphocytes that can?
Recognize cell surface changes (surface proteins) on virally-infected cells, foreign cells, and some tumor cells.
NK cells can bind to them and kill them
72
NK cells are activated by?
Interferons (cytokines) which are produced by virally-infected cells and sometimes also by lymphocytes
73
What are interferons and their role in viral infections?
A family of glycoproteins produced early in infection to block viral protein synthesis and activate immune responses
74
Interferons are produced when?
Very early in infection and form the first line of defense against viral infection
They act on NK cells and other cell types through specific membrane receptors influencing viral proteins and block synthesis of some proteins
75
Which phagocytic cells are part of the innate immune system?
Macrophages and polymorphonuclear leukocytes (PMNs)
76
Phagocyte means?
Cells that eat - by engulfing and destroying
They have pseudopodia that deform and go around molecules/particles to ingest them via fusion + destroy them with lysozymes
77
What is the function of phagocytic cells in immunity?
Recognize, ingest, and destroy foreign cells and components
78
What are the phagocytic cells?
Neutrophils and macrophages
79
Phagocytic activity is enhanced by?
Opsonization
80
Recognition of foreign organisms is enhanced by
Opsonization (i.e., depositing compounds such as complement (C3B), antibody, or both on the infectious agent - both leads to increased binding + phagocytic activity
Both macrophages and neutrophils have receptors for C3B and antibody
81
What are opsonins?
Molecules that initiate opsonization, such as complement C3b and antibodies
82
Which immune cells have receptors for C3b and antibodies?
Macrophages and neutrophils
83
What forms the reticuloendothelial system?
Phagocytic tissue macrophages and neutrophils.
84
Where is the reticuloendothelial system found?
In organs like bone marrow, spleen, and lymph nodes
85
How do monocytes become macrophages?
They are synthesized in the bone marrow, enter the blood, then migrate into tissues and differentiate into macrophages
86
What is the main function of cells in the reticuloendothelial system?
Phagocytosis—engulfing and destroying foreign particles and substances
87
Where in the body are phagocytic cells particularly concentrated due to high infection risk?
Skin and subcutaneous tissue, liver sinuses (Kupffer cells), spleen, bone marrow, lymph nodes, and alveoli
88
What is the role of phagocytic cells in circulation and tissues?
To clear particles and soluble substances from the body
89
Reticuloendothelial system
Network formed from the phagocytic tissue macrophages and neutrophils which is found in many organs including bone marrow, spleen, and lymph nodes
90
How are resident macrophages formed?
Myeloid-derived monocytes (precursor to macrophages) enter the blood and then tissues, then become macrophages and adapt to the environment
91
Which locations have increased number of phagocytic cells?
Skin and subcutaneous tissue, liver sinuses (Kupffer cells), spleen, bone marrow, lymph nodes, and alveola - increased possibility for infection
For example, when you breathe in dust, macrophages removal these particles
92
The reticuloendothelial system plays an important role in?
The clearance of particles and soluble substances in the circulation and tissues. These areas are concentrated with macrophages
93
What is the adaptive immune system?
A specific defense mechanism that improves with repeated infections and targets individual invading agents. Works in concert with innadaptive immune system
94
How does the adaptive immune system work with the innate immune system?
It works in concert to enhance overall immune defense
95
What are antigens?
Specific chemical compounds on foreign agents recognized by antibodies
96
What are antibodies also called?
Immunoglobulins (Ig) or gamma globulins
97
What is the structure of an antibody?
2 identical heavy chains + 2 identical light chains
98
What are the two functional regions of an antibody?
1. Fab (antigen-binding region) – variable, binds to antigen
2. Fc (crystalline fragment) – constant, binds to host tissues and complement
99
Antibodies are secreted and synthesized by
derivatives of B cells
100
Each antibody molecule is
Bifunctional - fragment antigen binding + fragment crystalline
101
What are the 2 portions of an antibody?
Variable portion (binds to antigen) and constant portion (binds to our own immune system)
102
Fab binds to a particular part of a molecule called
Antigenic determinant domain or epitope
103
What is an epitope?
The specific part of an antigen that the antibody binds to (antigenic determinant)
104
What molecular weight must epitopes typically exceed?
8000 Daltons
105
What type of reaction occurs between antigens and antibodies?
Highly specific, though cross-reactivity can occur
106
Ag-Ab reaction show what level of specificity?
High level but there is some level of cross-reactivity (binding not 100% but enough to activate antibody)
107
What are the different classes of Ig?
- IgG
- IgA
- IgM
- IgD
- IgE
108
What is the major Ig in circulation and secondary immune response?
IgG – 70-75% of circulating Igs; neutralizes toxins; crosses the placenta
109
Which Ig is dominant in mucosal secretions (milk, saliva)?
IgA – 15-20% of circulating Igs; provides passive immunity to newborns, in saliva, colostrum, milk, genito-urinary secretion
110
Which Ig is a pentamer and first produced in an immune response?
IgM – 10% of Igs; found in blood and lymph; short-lived. It's an early antibody against antigenically complex organisms it agglutinates (clumps) for easier breakdown
111
Which Ig is found on B cell (major form of them) membranes and may help in cell differentiation?
IgD – ~1% of circulating Igs. Major form on membrane of B-lymphocytes, may play a role in Ag triggering of lymphocyte differentiation
112
Which Ig is involved in parasitic immunity and allergic responses?
IgE – binds to mast cells and basophils. Present on surface of basophil and mast cells, involved in parasitic immunity and allergic reaction
113
Adaptive immune response involves 2 types of immunity
Humoral and cell-mediated
114
Humoral immunity
Production of specific antibodies (immunoglobulins) against the invading agents by B cells
115
Cell-mediated immunity
T cells specifically destroy the invading agents (makes physical contact - like NK cells)
116
What do B cells do in the adaptive immune system?
Produce specific antibodies (humoral immunity); mature in bone marrow
117
What do T cells do in the adaptive immune system?
Destroy infected or abnormal cells (cell-mediated immunity); develop in thymus
118
What is humoral immunity?
Antibody-mediated response carried out by B cells
119
What is cell-mediated immunity?
Immune response involving T cells attacking specific antigens
120
Where do B cells mature?
In bone marrow (in birds: in Bursa of fabricius)
121
Where do T cells develop?
In the thymus gland
122
The adaptive immune system is based on the ability of B cells and T cells to do what?
- B cells: to produce specific antibodies against Ag
- T cells: to specifically attack Ag
123
How does the body produce specific antibodies against a foreign antigen?
Clonal selection
124
There are estimated to be about _ types of preformed B cells and T cells
1 million
125
What can each B cell recognize and produce?
Only one specific antigen and its corresponding antibody
126
What triggers clonal selection?
Binding of an antigen to a specific B cell
127
What happens after a B cell is activated by an antigen?
It proliferates, forming many identical cells that produce specific antibodies
128
Each B cell is capable of producing and recognizing how many types of antigens?
Only 1 type
129
B cells contain surface binding proteins that are identical to?
The binding domain of the antibody they produce
130
In clonal selection, what happens when an antigen binds to a B cell?
Binds and activates a preformed B-cell leading to its proliferation, producing many of the same type of B cells that secret specific antibodies against the same antigen
Process is known as selection of the specific clones of antibody-producing B cells
131
Activation of B cells with an antigen results in?
Enlargement of the cells - some further differentiate and form plasma cells which proliferate and produce antibodies at an extremely rapid rate
132
A number of B-lymphocytes do not form plasma cells and form what instead?
Memory cells - have the membrane components to recognize the antigen
133
What are plasma cells?
Differentiated B cells that secrete large amounts of antibodies (gamma globulins)
134
What are memory cells?
B cells that don’t become plasma cells but remain in the body to recognize the antigen upon re-exposure
135
Together, the formation of plasma cells and memory cells after B-cell activation does what?
Increases the population of B cells that can get activated if there is further infection by the same Ag
136
What is the secondary immune response?
A faster, stronger response upon re-exposure to the same antigen due to memory cells
137
What is the basis of vaccination?
The secondary immune response and long-term memory cell formation
138
What helps improve and maintain memory cells?
Cytokines and cell division (mitosis)
139
The secondary response is the basis for which 2 processes?
Acquiring immune response and vaccination (contain adjuvants - stronger immune response)
140
What are the actions of antibodies?
Agglutination, neutralization, opsonization, complement activation
141
What is agglutination/precipitation?
Antibodies bind multiple organisms into clumps forming large insoluble complexes
142
What is neutralization?
Antibodies bind to and inactivate toxins or pathogens by altering structure or blocking active sites
143
How do antibodies aid in opsonization?
They tag pathogens, making them more easily recognized and ingested by phagocytes
144
What happens when an antigen binds to an antibody?
Complement binding sites in the Fc region are exposed, activating the complement cascade starting with C1
145
Activation of complements by antibodies C1-C9 a & b
Binding of Ag to Ab activates complement binding sites in the Fc chain which in turn activates C1 and thereby starting a cascade of activation of various compounds (leads to lysis of pathogen)
(CLASSICAL PATHWAY)
146
Major groups of T-cells
1. Helper t-cells
2. Cytotoxic T cells (killer cells)
3. Suppressor T cells
147
Helper T cells
Secretes cytokines, including interleukins, CSF, and interferon-g. Without helper T cells, the immune system would be very inefficient
148
Which disease develops due to helper T cell inactivation?
AIDS syndromes (immunodeficiency syndrome)
149
What do Cytotoxic T cells do?
Bind to antigens on infected or abnormal cells and kill them
150
How do Cytotoxic T cells kill target cells?
They secrete perforin to form holes and inject cytotoxic compounds, triggering apoptosis
151
Which infections or conditions are Cytotoxic T cells especially important for?
Viral infections and organ transplant rejection
152
What is the role of Suppressor (Regulatory) T cells?
Decrease activity of Helper T cells to regulate immune response
153
Why are Regulatory T cells important?
They help maintain self-immune tolerance and prevent autoimmune reactions
154
Perforin
Mediates whole formation in which cytotoxic compounds are injected - create an immunological synapse to secrete material + secondary messenger and initiates a cascade leading to apoptosis
155
What are cytotoxic T cells particularly lethal to?
Tissue cells infected by virus - makes them important for rejection of organ transplants
156
How can the immune system distinguish between foreign cells (antigen) and self?
Membranes of all cells (except RBC) are genetically marked with characteristic proteins known as histocompatibility molecules (AKA human leukocyte antigens, HLA)
Coded by a group of genes called major histocompatibility complex (MHC) - differences in MHC mark the cell as antigen
157
How many MHC molecules does an individual have?
3-6 types out of 100+ different MHC molecules
158
How does the immune system distinguish between self and non-self cells?
By recognizing histocompatibility molecules (HLA) encoded by the MHC gene complex on the membrane of all cells (except RBCs)
159
What are HLA molecules and who codes for them?
Human leukocyte antigens, coded by the Major Histocompatibility Complex (MHC)
160
Why is MHC important for organ transplantation?
The closer the MHC match, the more compatible the tissue. Only identical twins have identical MHC
161
Histocompatability
The chances that 2 individuals have the same combinations of MHC are small - the closer the match, the more histocompatible the tissues (only identical twins have identical MHC)
this is important for transplantation
162
Can antigens activate T cells on their own?
No, they must be presented by macrophages or infected cells bound to MHC molecules
163
What cells express Class I MHC?
All nucleated cells except RBCs
164
What T cells recognize Class I MHC?
Cytotoxic T cells (via CD8 coreceptor)
165
What cells express Class II MHC?
Macrophages and B-cells
166
What T cells recognize Class II MHC?
Helper T cells (via CD4 coreceptor)
167
Class-1 MHC
Produced/expressed by all cells except by RBCs and recognized only by cytotoxic T cells
168
Class-2 MHC
Expressed only by macrophages and B-cells and recognized only by helper T cells
169
Killer T cells only interact with Ag presented with which MHC and contain which coreceptor?
Class-1 and CD8
170
Helper T cells only interact with Ag presented with which MHC and contain which coreceptor?
Class-2 and CD4
171
Restriction of the type of T cell interacting with either class-1 and class-2 MHCs is due to?
Presence of coreceptors (CD4 and CD8) which are proteins associated with T cell receptors for MHC
172
How are B cells activated?
Both by direct binding to antigen (clonal selection) as well as antigen presented by other leukocytes/macrophages (antigen presentation) and secretion by helper T cells
173
Suppressor T cells
Act as regulatory cells - results in a reduction in the activity of helper T cells. Suggested to be important for self immune tolerance
174
What happens if something goes wrong with suppressor T cells?
Leads to autoimmune disease (body starts attacking itself)
175
2 possible mechanisms of immune tolerance
Clonal deletion and clonal anergy
176
Clonal deletion (immune tolerance)
Destruction of lymphocytes that have receptors for self (cells with identical MHC) during development and fetal stages
177
Clonal anergy (immune tolerance)
Lymphocytes directed against self antigens may be present, but do not attack self antigen (containing identical MHC) - suppressor T cells play a role
178
Allergy
Hypersensitivity - reactivity to an antigen which can result in pathologic reactions upon subsequent exposure to that particular antigen
It involves mast cells/Basophils with IgE antibodies
179
What causes inflammatory response in allergies?
histamine, bradykinin, serotonin, prostaglandins, reaction products of complement system, reaction products of blood-clotting systems and hormonal substances known as lymphokines (released by sensitized T cells)
180
What do the tissue products released by mast cells/basophils that cause inflammatory response lead to?
- Attraction of tissue macrophages
- Increase in neutrophils (5 fold)
- Attracts monocytes from blood to enter the inflamed area and swell to become
- Macrophages (to increase phagocytic capability)
- Increase production of granulocytes and monocytes by bone marrow from committed stem cells
- Vasodilation of local blood vessels and excess blood
- Increased permeability of capabilities and increased interstitial fluid
- Clotting of interstitial fluid as a result of increase leakage of fibrinogen - "walling off"
- Swelling of tissue cells
181
What does histamine do?
Increased permeability of capillaries (even proteins can pass through membrane) which increases colloid/oncotic pressure and attracts more fluid, leading to swelling or edema
182
Where does the name C-reactive protein come from?
Named because they bind to c-protein of pneumococci - stimulated by inflammation and infection (massive increase after infection)
183
What coreceptor do Cytotoxic T cells have and what MHC do they respond to?
CD8; responds to Class I MHC
184
What coreceptor do Helper T cells have and what MHC do they respond to?
CD4; responds to Class II MHC
185
How are B cells activated?
By direct antigen binding and antigen presentation via macrophages and cytokines from Helper T cells
186
What is immune tolerance?
The immune system’s ability to not attack self-antigens
187
What are the two mechanisms of immune tolerance?
Clonal deletion and clonal anergy
188
What is clonal deletion?
Destruction of lymphocytes with self-reactive receptors during development
189
What is clonal anergy?
Lymphocytes recognize self-antigens but are inactive, partly due to Suppressor T cells
190
What is hypersensitivity?
An exaggerated immune reaction to an antigen upon re-exposure
191
What characterizes inflammation?
Vasodilation, increased capillary permeability, fluid leakage, clotting in interstitial space, and immune cell infiltration
192
What is the purpose of the “walling off” process in inflammation?
To prevent the spread of infectious organisms and toxins
193
Name inflammatory mediators
Histamine, bradykinin, serotonin, prostaglandins, complement system products, clotting products, and lymphokines
194
What immune responses are induced during inflammation?
- Macrophage attraction
- Neutrophilia (↑ neutrophils)
- Monocyte infiltration and macrophage differentiation
- Increased granulocyte/monocyte production in bone marrow (up to 50×)
