Inflammatory Cells in the Airway

Question 1

Describe the structure of the respiratory tract

Answer 1

NALT

Trachea

BALT

Bronchiole

Alveoli

NALT = Nasal Associated Lymphoid Tissue; BALT = Bronchus Associated Lypmhoid Tissue

Question 2

Describe the types of cells found in and around NALT

Answer 2

Epithelial cells

M Cells

Goble tcells

Intraepithelial Lymphocytes

Question 3

What do mature B-cells predominantly express

Answer 3

IgA

Question 4

Where is BALT usually found and what cells are involved?

Answer 4

Lower airways at bronchiole branches

Germinal centre consisting of B-cell follicle and T-cell area interspersed with macrophages and dendritic cells

Question 5

Compare the overall structure of NALT and BALT

Answer 5

NALT are more defined areas whereas BALT are more diffused.

Question 6

There is a school of thought that respiratory disease occurs due to disrupted lung _____ (ie immune response vs _____ _____). Some challenges to maintenance of homeostasis include:

• Air pressure
• Endogenous _____ flora in lower airways
• Inhaled _____, particulate matter and pollution

Key point: Lung immunity is a balance between maintaining homeostasis and mounting an appropriate immune response to threat

Answer 6

There is a school of thought that respiratory disease occurs due to disrupted lung homeostasis (ie immune response vs gas exchange). Some challenges to maintenance of homeostasis include:

• Air pressure
• Endogenous microbial flora in lower airways
• Inhaled antigens, particulate matter and pollution

Key point: Lung immunity is a balance between maintaining homeostasis and mounting an appropriate immune response to threat

Question 7

Describe some features of the airway epithelium that are first-line in preventing an immune response (5)

Answer 7

• Ciliated epithelium
• Mucus and glycocalyx
• Tight Junctions
• Rapid epithelial cell turnover
• Microflora

Question 8

Name some cells found in the large airways (conducting zone) (4)

Answer 8

• Ciliated epithelial cells
• Goblet Cells
• Basal Cells
• Neuoendocrine cells - samples for oxygen

Question 9

Name some cells found in the small airways (3)

Answer 9

1. Ciliated Epithelial Cells
2. Club cells - secrete glycosaminoglycans and solution similar to surfactant
3. Basal Cells

Question 10

Name some cells found in the alveoli (lower airways)

Answer 10

Type I Alveolar Epithelial Cells

Type II Alveolar Epithelial Cells

Question 11

Where is there more mucus secretion: upper or lower airways

Answer 11

Upper airways

Lower airways need less so that gas exchange is not hindered

Question 12

Describe the function of cilia and mucus

Answer 12

Mucociliary Clearance

Ciliated epithelial cells transport mucus upwards and outwards to expell pathogens

Question 13

What is the function of IgA when it is secreted into the mucosa

Answer 13

IgA can opsonise bacteria

Aggregation of bacteria

More phagocytosis and easier mucociliary clearance

Question 14

Describe the structure of IgA

Answer 14

• Can form dimers
  
  • J chain
  • Secretory component
• J chain binds to IgA receptor on epithelial cells

Question 15

How does IgA get from the lamina propria to the airway lumen

Answer 15

Trancytosis

IgA released by Plasma B cells

Dimerised with J chain

J Chain binds to IgA receptor

Endocytosis and movement of the endosome to the apical side

Secretion of IgA with a secretory component

Question 16

Initial colonisation of airways by alveolar macrophages occurs in the first few days of birth and is dependent on fetal _____. These differentiate into macrophage subtypes depending on the environment they are in - they are referred to as _____-_____ macrophages.

Answer 16

Initial colonisation of airways by alveolar macrophages occurs in the first few days of birth and is dependent on fetal monocytes. These differentiate into macrophage subtypes depending on the environment they are in - they are referred to as tissue-resident macrophages.

Question 17

Tissue resident macrophages are involved in normal physiology as well as pathology. Give some examples of pathology.

Answer 17

Microglia - neurodegeneration

Osteoclast/blast - osteoporosis

Atherosclerosis

Kupffer cells - fibrosis

Question 18

Tissue resident macrophages are replenished throughout life through in situ _____ and self-renewal. Exposure to envrionmental factors (fibrosis, pollutants) lead to release of monocytes from the _____ _____ - these then differentiate into _____ (Ly6c+) and _____-_____ (Ly6c-). Ly6c+ differentiate into tissue resident macrophages. These cells are more _____ as they are dervied from cells produced in response to _____.

Answer 18

Tissue resident macrophages are replenished throughout life through in situ proliferation and self-renewal. Exposure to envrionmental factors (fibrosis, pollutants) lead to release of monocytes from the bone marrow - these then differentiate into circulatory (Ly6c+) and non-circulatory (Ly6c-) monocytes. Ly6c+ differentiate into tissue resident macrophages. These cells are more inflammatory as they are dervied from cells produced in response to stress.

Question 19

As we age, there is depletion of our _____-derived tissue resident macrophages. These are replensihed by _____ _____-derived monocytes, which are pro-inflammatory.

Answer 19

As we age, there is depletion of our fetal-derived tissue resident macrophages. These are replensihed by bone marrow-derived monocytes, which are pro-inflammatory.

Question 20

What are the two ‘general’ phenotypes of macrophages

Answer 20

M1 - pro-inflammatory

M2 - Tissue-healing

In reality, macrophages express same receptors but in different ratios - no distinct receptor expression

Question 21

Name some proteins produced by M2 macrophages which are involved in tissue healing

Answer 21

IL-4

IL-10

TGF-B

IGF-1

MMP-9

Arginase -> polyamines and collagen

Question 22

Name some proteins produced by M1 macrophages that are involved in inflammation

Answer 22

TNF-a

IL-6

IL-1

IFN

CXCL 9, 10, 11

Question 23

Name surface markers found on alveolar macrophages (4)

Answer 23

CD11c+

CD200R

CD206

SIGLEC-F

SIGLEC-F = Sialic Acid-Binding Immunoglobulin-like Lectin F

Question 24

Describe the process of macrophage phagocytosis

Answer 24

1. Phagocytosis of pathogen
2. Formation of phagosome
3. Lysosome and phagosome fuse to make phagolysosome
4. Pathogen degraded into fragments
5. Antigens presented on APC surface (MHC)
6. Leftover fragment exocytosed

Question 25

Alveolar macrophages have poor _____ \_\_\_\_\_ ability and produce _____ levels of ROS. They are naturally _____ under steady state.

Answer 25

Alveolar macrophages have poor **_antigen_** **_presenting_** ability and produce **_low_** levels of ROS. They are naturally **_hyporesponsive_** under steady state.

Question 26

Neutrophils are continuously generated in the bone marrow from myeloid precursors. Name the upstream signalling that leads to neutrophil release from bone marrow

Answer 26

Macrophage release **IL-23** **Th17** matures and releases **IL-17A** Stimulates **fibroblasts** to release **G-CSF** Causes **release** of neutrophils from bone marrow

Question 27

What two transcription factors control maturation of neutrophils

Answer 27

PU.1 C/EBP *CCAAT-enhancer-binding proteins*

Question 28

Name the 6 stages of neutrophil development

Answer 28

Myeloblast **Pro**myelo**cyte** Myelocyte **Meta**myelocyte Band Neutrophil

Question 29

Outline the process of neutrophil recruitment from the blood stream (5)

Answer 29

1. Free circulating Neutrophil 2. Rolling 1. Tethering 2. Slow Rolling 3. Adhesion 1. Full Arrest 2. Firm Adhesion 4. Crawling 5. Transmigration 1. Paracellular 2. Transcellular

Question 30

Describe the process of tethering and rolling with regards to adhesion molecules involved

Answer 30

Tethers bind to endothelial **P-selectin** via its ligand **PSGL1** PSGL1 forms patches along the whole projection that attach and pull apart sequentially - **step-wise peeling of slings** Deceleration from neutrophil **LFA1** to endothelial **ICAM2** *PSGL1 = P-selectin glycoprotein ligand 1; LFA1 = Lymphocyte function-associated antigen 1; ICAM2 = intercellular adhesion molecule 2*

Question 31

Neutrophils can be short- and 'longer'-lived. Explain the relevance as to why neutrophils can be both.

Answer 31

_Short-lived_ * Limit potential to cause damage * Secondary necrosis * Die through apoptosis to protect surrounding tissue _Long-lived_ * Extended life span to ensure pathogens are cleared * Enables orchestration/regulation of other aspects of inflammatory response

Question 32

How can neutrophils kill pathogens (bacteria)

Answer 32

1. ROS 1. NADPH oxygenase-dependent mechanism (NOX) 2. Anti-bacterial proteins 1. Cathepsins 2. Defensins 3. Lactoferrin 4. Lysosyme 3. NETs 1. Genetic material trapping pathogens

Question 33

NETs are composed of _____ and granule proteins (serine proteases, neutrophil elastase). They trap and kill extracellular pathogens. The neutrophils sense the _____ of the pathogen and release NETs if they are too big.

Answer 33

NETs are composed of **_chromatin_** and granule proteins (serine proteases, neutrophil elastase). They trap and kill extracellular pathogens. The neutrophils sense the **_size_** of the pathogen and release NETs if they are too big.

Question 34

Neutrophils don't just kill pathogens, they also have _____ activity, producing pro-inflmmatory, anti-inflammatory, immunoregulatory, angiogenic and fibrogenic cytokines

Answer 34

Neutrophils don't just kill pathogens, they also have **_biosynthetic_** activity, producing pro-inflmmatory, anti-inflammatory, immunoregulatory, angiogenic and fibrogenic cytokines

Question 35

What do neutrophils produce to activate NK cells during infection

Answer 35

IL-12 (DC), IL-18 (neutrophils) Stimulates NK cell IFN-γ produciton

Question 36

Neutrophils can present antigens to _____ cells, promoting their maturation and capacity to mediate T cell proliferation and polarisation. Neutrophils also release chemokines to promote T cell (\_\_\_\_\_ and \_\_\_\_\_) recruitment. Neutrophils can also facilitate T cell-independent anitbody response by marginal zone B cells

Answer 36

Neutrophils can present antigens to **_dendritic_** cells, promoting their maturation and capacity to mediate T cell proliferation and polarisation. Neutrophils also release chemokines to promote T cell (**_Th1_** and **_Th17_**) recruitment. Neutrophils can also facilitate T cell-independent anitbody response by marginal zone B cells

Question 37

Neutrophils are also \_\_\_\_\_-\_\_\_\_\_, producing _____ and pro-resolving lipid mediators. They can also negatigvely regulate T cell function.

Answer 37

Neutrophils are also **_anti_**-**_inflammatory_**, producing **_IL-10_** and pro-resolving lipid mediators. They can also negatigvely regulate T cell function.