Innate Immunity Flashcards
(148 cards)
1
Q
Why are neutrophils also called polymorphonuclear leukocytes (PMNs)?
A
Because their nucleus is segmented into 3-5 lobules giving them a multilobed appearance.
2
Q
What are the two types of granules in neutrophils?
A
- Specific granules: Contain lysozyme collagenase
- Azurophilic granules: Contain myeloperoxidase, defensins
3
Q
What is the main function of neutrophils in innate immunity?
A
Phagocytosis of microbes and debris followed by destruction in phagolysosomes.
4
Q
What is NETosis?
A
A process where neutrophils extrude their nuclear contents to form Neutrophil Extracellular Traps (NETs) immobilizing and killing extracellular microbes.
5
Q
What are the two sources of macrophages in tissues?
A
- Monocyte-derived macrophages (from circulating blood monocytes).
- Tissue-resident macrophages (from yolk sac or fetal liver precursors).
6
Q
What is the major growth factor for monocyte/macrophage differentiation?
A
Macrophage Colony-Stimulating Factor (M-CSF).
7
Q
What are the two subsets of monocytes?
A
- Classical (inflammatory) monocytes: Highly phagocytic, recruited to infection sites.
- Nonclassical (patrolling) monocytes: Crawl along endothelium, scavenge particles, and aid endothelial repair.
8
Q
What is the process of clearing apoptotic cells by macrophages called?
A
Efferocytosis.
9
Q
What are the five major functions of macrophages?
A
- Phagocytosis & killing of microbes.
- Sentinel function (cytokine secretion for immune activation).
- Pyroptosis (inflammatory cell death via inflammasome activation).
- Antigen presentation to T cells.
- Tissue repair & fibrosis (angiogenesis & collagen synthesis).
10
Q
Why do macrophages dominate later stages of inflammation compared to neutrophils?
A
- Macrophages live longer at infection sites.
- They can divide at inflammation sites, while neutrophils cannot.
11
Q
What cytokine is essential for mast cell development?
A
Stem Cell Factor (c-KIT ligand).
12
Q
Where are mast cells mainly found?
A
In tissues, especially skin & mucosal epithelia, near blood vessels & nerves.
13
Q
What are the main components of mast cell granules?
A
Histamine and acidic proteoglycans (bind basic dyes, making granules stain dark blue).
14
Q
How do mast cells get activated?
A
- IgE binding to high-affinity FcεRI receptors → allergic responses.
- Microbial product recognition (independent of IgE) → innate immune response.
15
Q
What is the primary immune function of eosinophils?
A
Defense against helminths (parasitic worms) and involvement in allergic reactions.
16
Q
What type of granules do eosinophils contain?
A
Major Basic Protein (MBP), eosinophilic peroxidase, and enzymes toxic to helminths.
17
Q
How do basophils differ from mast cells?
A
- Basophils circulate in blood, while mast cells reside in tissues.
- Both release histamine and play a role in allergic responses.
18
Q
What are the three types of antigen-presenting cells (APCs)?
A
Dendritic cells, macrophages, and B cells.
19
Q
What is the main function of dendritic cells?
A
Capture antigens in peripheral tissues and migrate to lymph nodes to activate T cells.
20
Q
What is the main cytokine for neutrophil production?
A
Granulocyte Colony-Stimulating Factor (G-CSF).
21
Q
What is the function of the inflammasome?
A
Activates caspase-1, which processes IL-1β and IL-18, triggering pyroptosis and inflammation.
22
Q
What is the lifespan of monocytes in circulation?
A
1 to 7 days.
23
Q
How do tissue-resident macrophages maintain their population?
A
Self-renewal (they proliferate locally without needing bone marrow monocytes).
24
Q
Give three examples of specialized tissue-resident macrophages.
A
- Kupffer cells (liver).
- Alveolar macrophages (lungs).
- Microglial cells (brain).
25
What cytokines do macrophages release to recruit immune cells?
TNF, IL-1, and IL-6, which promote leukocyte recruitment and activation.
26
Why do neutrophils dominate early stages of infection?
- Rapid recruitment from blood.
- High phagocytic activity.
- Short lifespan (~6-24 hours in tissues).
27
What happens to neutrophils after they kill pathogens?
They undergo apoptosis, and macrophages remove them via efferocytosis.
28
What are the two major activation states of macrophages?
- Classically activated (M1) macrophages → Pro-inflammatory, antimicrobial.
- Alternatively activated (M2) macrophages → Anti-inflammatory, tissue repair.
29
What is the primary function of M1 macrophages?
- Phagocytosis of microbes.
- Secretion of pro-inflammatory cytokines (IL-1, TNF, IL-6).
- ROS and NO production to kill pathogens.
30
What is the primary function of M2 macrophages?
- Tissue remodeling and repair.
- Secretion of IL-10 and TGF-β (anti-inflammatory cytokines).
31
What are the major steps of inflammation?
1. Recognition of microbes/damage (via PRRs).
2. Recruitment of leukocytes (TNF, IL-1, chemokines).
3. Phagocytosis & microbe destruction.
4. Resolution & tissue repair (M2 macrophages).
32
What role do chemokines play in immune responses?
Guide leukocytes to infection sites via chemotaxis.
33
What is the difference between acute and chronic inflammation?
- Acute inflammation: Rapid onset, dominated by neutrophils.
- Chronic inflammation: Prolonged, dominated by macrophages and lymphocytes.
34
What are the three main steps of phagocytosis?
1. Recognition & attachment (opsonization by antibodies/complement).
2. Engulfment (formation of a phagosome).
3. Killing & degradation (fusion with lysosome → phagolysosome).
35
What are the two major killing mechanisms in phagolysosomes?
- ROS & NO production (oxidative burst).
- Lysosomal enzymes (proteases, defensins).
36
What are the major functions of mast cells?
- Allergic reactions (IgE-mediated degranulation).
- Release of histamine & inflammatory mediators.
- Defense against parasites.
37
What is the function of histamine in mast cell activation?
- Vasodilation, increased vascular permeability.
- Smooth muscle contraction (e.g., in asthma).
38
How do eosinophils kill helminths?
Release of toxic granules (Major Basic Protein, Eosinophilic Peroxidase).
39
What is the role of antigen-presenting cells (APCs)?
- Process and present antigens via MHC molecules.
- Activate naïve T cells in lymph nodes.
40
Which APCs are the most potent in T cell activation?
Dendritic cells.
41
What are the two main types of MHC molecules?
- MHC-I → Presents intracellular antigens to CD8+ T cells.
- MHC-II → Presents extracellular antigens to CD4+ T cells.
42
What is cross-presentation?
A process where dendritic cells take up extracellular antigens and present them via MHC-I to CD8+ T cells.
43
What is the main function of memory T and B cells?
Faster, stronger immune response upon re-exposure to the same pathogen.
44
Why is secondary immune response faster than primary?
- Memory cells are pre-formed.
- Stronger antibody affinity.
- Faster clonal expansion.
45
What are the primary functions of macrophages in immunity?
Phagocytosis and killing of microbes, cytokine secretion to amplify immune response, clearance of apoptotic and necrotic cells (efferocytosis), antigen presentation to T cells, promotion of tissue repair and angiogenesis.
46
What is efferocytosis?
The process by which macrophages clear apoptotic cells to maintain tissue homeostasis and prevent inflammation.
47
What are tissue-resident macrophages' main roles?
Act as sentinel cells: detect microbes and secrete cytokines to start immune responses.
48
What is pyroptosis?
Inflammatory cell death triggered by microbes via the inflammasome, releasing cytokines that enhance inflammation.
49
How do macrophages become activated?
By PRRs (e.g., TLRs) detecting microbial molecules, by cytokines or membrane proteins from T cells, by opsonin receptors (e.g., complement, IgG).
50
What is a TLR (Toll-like Receptor)?
A type of PRR that detects microbial components like LPS, flagellin, or viral RNA, leading to activation of innate immune responses.
51
What does PRR stand for, and what is its role?
Pattern Recognition Receptor – detects conserved microbial structures (PAMPs) and triggers innate immune responses.
52
What does PAMP stand for?
Pathogen-Associated Molecular Pattern – microbial molecules recognized by PRRs (e.g., LPS, dsRNA, flagellin).
53
What's the relationship between PRRs and PAMPs?
PRRs (like TLRs) detect PAMPs to initiate immune responses—similar to scanners detecting suspicious items.
54
What are M1 and M2 macrophages?
M1 (classically activated): Induced by cytokines to kill microbes. M2 (alternatively activated): Induced to promote tissue repair and fibrosis.
55
What do mast cells, basophils, and eosinophils have in common?
All are granulocytes involved in defense against helminths, allergic reactions, and contain granules with inflammatory mediators.
56
Where are mast cells found and what promotes their development?
Found in skin and mucosal tissues, near blood vessels. Development requires stem cell factor (c-KIT ligand).
57
What triggers mast cell degranulation?
IgE binding to antigen on FcεRI receptor
Recognition of microbial products via PRRs (innate)
58
What mediators are released by mast cells?
Preformed: Histamine, proteases
Newly synthesized: Cytokines (e.g., TNF), lipid mediators (e.g., prostaglandins)
59
How do mast cells and basophils differ?
Mast cells are tissue-resident
Basophils circulate in blood
Both have IgE receptors and similar functions
60
What do mast cells, basophils, and eosinophils have in common?
All are granulocytes that protect against helminths and participate in allergic responses, and contain cytoplasmic granules with inflammatory mediators.
61
Where are mast cells found, and what promotes their development?
In tissues (skin, mucosa) near blood vessels. Stem cell factor (c-KIT ligand) is essential for their development.
62
What receptors do mast cells use to detect antigens?
FcεRI receptors for IgE and PRRs for microbial products.
63
What is the main difference between mast cells and basophils?
Mast cells are tissue-resident, while basophils circulate in blood.
64
What do eosinophils' granules contain and what are their effects?
Basic proteins and enzymes that kill parasites but can also damage host tissue.
65
Which cytokines promote eosinophil development?
GM-CSF, IL-3, and IL-5 (IL-5 is most specific).
66
What receptors are found on eosinophils?
Fc receptors (IgA, IgG), TLRs, IL-5 receptors.
67
Where are eosinophils typically located in the body?
Low levels in blood and mucosal tissues (respiratory, GI, genitourinary tracts). Numbers increase during inflammation.
68
What does PRR stand for in immunology?
Pattern Recognition Receptor
69
What do PRRs recognize?
Pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMPs)
70
Where are TLRs typically located?
Plasma membrane and endosomal membranes
71
What is the main function of PRRs?
To detect infection and initiate immune responses
72
How do PRRs contribute to immune response specificity?
By detecting the type and location of infection to tailor the immune response
73
What does TLR stand for?
Toll-like receptor
74
How many TLRs are identified in humans?
TLR1 to TLR9
75
Which cells express TLRs?
Dendritic cells, phagocytes, B cells, endothelial cells, and others
76
What does NLR stand for?
NOD-like receptor
77
Where are NLRs located?
In the cytosol
78
What is the outcome of RLR activation?
Production of type I interferons
79
What do cytosolic DNA sensors detect?
Microbial or abnormal host DNA in the cytosol
80
Name a cytosolic DNA sensor involved in inflammasome activation.
AIM2
81
Which pathway is associated with cytosolic DNA sensing?
cGAS-STING pathway
82
What is the effect of cytosolic DNA sensing?
Induces type I interferons and inflammation
83
Where are cytosolic DNA sensors found?
In the cytosol of many cell types
84
What does CLR stand for?
C-type lectin receptor
85
Where are CLRs found?
On the plasma membrane of phagocytes
86
Name two examples of CLRs.
Dectin-1 and Dectin-2
87
What do CLRs recognize?
Carbohydrates on microbial surfaces, such as mannose and β-glucans
88
What is the function of CLRs?
Trigger phagocytosis and inflammation in response to fungi and bacteria
89
Where are scavenger receptors located?
On the plasma membrane of phagocytes
90
Name one scavenger receptor.
CD36
91
What do scavenger receptors recognize?
Modified host molecules and bacterial components
92
What is the role of scavenger receptors?
Clear apoptotic cells and pathogens
93
Are scavenger receptors PRRs?
Yes, they are a type of PRR
94
Where are N-formyl peptide receptors located?
On the plasma membrane of phagocytes
95
Name an N-formyl peptide receptor.
FPR or FPRL1
96
What do N-formyl peptide receptors detect?
Bacterial and mitochondrial N-formylmethionyl peptides
97
What is the effect of N-formyl peptide receptor activation?
Chemotaxis and immune cell recruitment
98
Are these receptors involved in innate immunity?
Yes
99
Why is PRR location important?
It determines the type and location of pathogen detection
100
What does PRR activation lead to?
Effector functions such as cytokine production and inflammation
101
What determines the immune response specificity?
The type of PRR and its associated signaling pathways
102
Why is cytosolic detection critical?
Some pathogens or their components escape into the cytosol
103
What are common downstream effects of PRR signaling?
Inflammation, interferon production, and adaptive immunity activation
104
What does PRR stand for in immunology?
Pattern Recognition Receptor
105
What do PRRs recognize?
Pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMPs)
106
Where are TLRs typically located?
Plasma membrane and endosomal membranes
107
What is the main function of PRRs?
To detect infection and initiate immune responses
108
How do PRRs contribute to immune response specificity?
By detecting the type and location of infection to tailor the immune response
109
What does TLR stand for?
Toll-like receptor
110
How many TLRs are identified in humans?
TLR1 to TLR9
111
Which TLR recognizes LPS?
TLR4
112
Which TLRs are found in endosomes and detect viral nucleic acids?
TLR3, TLR7, TLR8, TLR9
113
Which cells express TLRs?
Dendritic cells, phagocytes, B cells, endothelial cells, and others
114
What does NLR stand for?
NOD-like receptor
115
Where are NLRs located?
In the cytosol
116
Name two NLRs involved in recognizing bacterial peptidoglycan.
NOD1 and NOD2
117
What immune complex can some NLRs form?
Inflammasomes
118
What cytokine is activated by inflammasomes?
IL-1β
119
What does RLR stand for?
RIG-I-like receptor
120
Where are RLRs located?
Cytosol of phagocytes and other cells
121
Name two RLRs.
RIG-I and MDA5
122
What do RLRs primarily detect?
Viral RNA
123
What is the outcome of RLR activation?
Production of type I interferons
124
What do cytosolic DNA sensors detect?
Microbial or abnormal host DNA in the cytosol
125
Name a cytosolic DNA sensor involved in inflammasome activation.
AIM2
126
Which pathway is associated with cytosolic DNA sensing?
cGAS-STING pathway
127
What is the effect of cytosolic DNA sensing?
Induces type I interferons and inflammation
128
Where are cytosolic DNA sensors found?
In the cytosol of many cell types
129
What does CLR stand for?
C-type lectin receptor
130
Where are CLRs found?
On the plasma membrane of phagocytes
131
Name two examples of CLRs.
Dectin-1 and Dectin-2
132
What do CLRs recognize?
Carbohydrates on microbial surfaces, such as mannose and β-glucans
133
What is the function of CLRs?
Trigger phagocytosis and inflammation in response to fungi and bacteria
134
Where are scavenger receptors located?
On the plasma membrane of phagocytes
135
Name one scavenger receptor.
CD36
136
What do scavenger receptors recognize?
Modified host molecules and bacterial components
137
What is the role of scavenger receptors?
Clear apoptotic cells and pathogens
138
Are scavenger receptors PRRs?
Yes, they are a type of PRR
139
Where are N-formyl peptide receptors located?
On the plasma membrane of phagocytes
140
Name an N-formyl peptide receptor.
FPR or FPRL1
141
What do N-formyl peptide receptors detect?
Bacterial and mitochondrial N-formylmethionyl peptides
142
What is the effect of N-formyl peptide receptor activation?
Chemotaxis and immune cell recruitment
143
Are these receptors involved in innate immunity?
Yes
144
Why is PRR location important?
It determines the type and location of pathogen detection
145
What does PRR activation lead to?
Effector functions such as cytokine production and inflammation
146
What determines the immune response specificity?
The type of PRR and its associated signaling pathways
147
Why is cytosolic detection critical?
Some pathogens or their components escape into the cytosol
148
What are common downstream effects of PRR signaling?
Inflammation, interferon production, and adaptive immunity activation
