Week 3 Lecture 4 - Macrophages

Question 1

Macrophage Function

Answer 1

Recognise bacterial pathogen by pattern recognition receptors
- e.g. Toll-like receptors
Trap in phagosome which fuses with lysosome
Phagolysosome digests particles
- enzymes and toxic free radicals
- pH changes
- release debris
- release of cytokines
Also remove dead/dying cells and toxic materials

Question 2

Macrophage Origin

Answer 2

1. Tissue-resident: develop early during embryogenesis (yolk sak and fetal liver)
2. Monocyte-derived: develop from bone marrow -> monocyte in blood -> macrophage

Question 3

Macrophage M1 vs M2

Answer 3

Nomenclature based around Th1 and Th2
- M1 stimulate Th1 and M2 stimulate Th2
M1 or M2 dominant responses can be independent from T cells
M1 = ‘fight’ response
M2 = ‘fix’ response

Question 4

M1 Macrophage Properties

Answer 4

Co-stimulatory markers
- CD40, CD80, CD86
Pro-inflammatory
- interleukin-6
- tumour necrosis factor
Nitric Oxide
Pro-inflammatory, therefore “Fight”
Anti-microbial and anti-tumour
Recruit cytotoxic T cells and Th1 cells

Question 5

M2 Macrophage Properties

Answer 5

Mannose/scavenger receptors
- CD206, CD163
Anti-inflammatory
- interleukin-10
- transforming growth factor-β
Arginase
Anti-inflammatory, therefore “Fix”
Wound healing and tumour growth
Recruit Th2 and Treg cells

Question 6

Macrophages in Tissue Injury - Early vs Late Response

Answer 6

Early during response
- M1 macrophages mediate tissue damage and initiate inflammatory responses
- recruit other immune cells through chemokine release e.g. CCL2 and CX3CL1
Late during response
- M2 macrophages mediate repair via tissue inhibitors of metalloproteinases (to block matrix degradation) and growth factors (e.g. TGF-β)
- limit M1 activity (and tissue damage) by secretion of IL-10

Question 7

M1 Nitric Oxide vs M2 Arginase

Answer 7

Nitric Oxide produced by M1
- inhibits cell proliferation
- induces cytotoxicity
Arginase produced by M2
- converts arginine to ornithine
- promotes proliferation and repair
Both compete for arginine at tissue site

Question 8

Wound Healing

Answer 8

1. M1 macrophages phagocytose debris, secrete pro-inflammatory factors -> recruit
2. Fibrosis and extracellular matrix remodelling occurs
3. M2 polarisation, secrete anti-inflammatory factors, inhibit M1 -> resolution
   Highly coordinated -> linked to macrophage activation state

Question 9

Chronic Venous Ulcers

Answer 9

Failure to switch from M1 to M2 phenotype
Haemorrhage and tissue damage leads to excess red blood cells
Iron overload sustains M1 activation

Question 10

Autoimmunity

Answer 10

SLE: sustained pro-inflammatory activation
Rheumatoid arthritis: synovial macrophages produce M1 cytokines (e.g. TNF, IL-1β, IL-12) and numbers correlate with disease

Question 11

Crohn’s Disease

Answer 11

Healthy = tissue-resident M2
Crohn’s = compromised gut
M1 macrophages infiltrate
Further infiltration of muscular layer and mesenteric fat

Question 12

Macrophages and Infection

Answer 12

Bacteria
- M1 macrophages responsible for resistance against intracellular pathogens
- e.g. Listeria monocytogenes, Salmonella typhimurium
- uncontrolled M1 associated with acute infections of E.coli and Streptococcus
- ->Gastroenteritis, urinary tract infections, meningitis, sepsis
Parasites
- macrophages undergo switch from M1 to M2 which is protective
Viruses
- polarisation to M2 in HIV, Herpes and respiratory syncytial virus infections can reduce inflammation and epithelial damage

Question 13

Allergy and Asthma

Answer 13

Asthma thought to be driven by Th2 cells which secrete IL-4 and IL-13
IL-4 and IL-13 polarise macrophages to M2
Collagen deposition and tissue remodelling by macrophages
M2 macrophages also secrete IL-13 driving Th2 responses

Question 14

Macrophages in Obesity and Metabolism

Answer 14

Adipose macrophages from lean mice/humans are M2
Obesity-associated insulin resistance and diabetes -> subclinical inflammation
-adipocytes release pro-inflammatory CCL2 and TNF -> recruit macrophages
- adipose macrophages secrete TNF, IL-6 which counteracts insulin-sensitising action of adiponectin and leptin -> insulin resistance

Question 15

Macrophages in Cancer

Answer 15

Cancer-related inflammation recruits monocytes -> macrophages
M1 are recruited and become “tumour-educated” M2 in response to tumour-derived factors e.g. IL-10, CCL2, TGF-β
Tumours often have hypoxic regions
- promote M2 macrophages which stimulate angiogenesis via release of vascular endothelial growth factor (VEGF)
Stages:
1. Tumour recruits macrophages
2. Macrophages drive tumour growth and angiogenesis
3. Tumour cells and macrophages suppress T cell activity
4. Support tumour cell migration and metastasis

Question 16

Aging and Macrophages

Answer 16

Elderly people have slow wound healing, decreased ability to fight infections, increased incidence of cancer
Macrophages in the elderly exhibit dysregulated inflammatory responses :
- decreased phagocytosis
- produce more anti-inflammatory cytokines e.g. TGF-β, IL-10
- less pro-inflammatory cytokines e.g. IFNγ
- promote T cell production of IL-10

Question 17

Targeting Macrophages in Cancer

Answer 17

Block macrophage recruitment
- anti-CCL2 antibody
- VEGF inhibitors
- anti-CSF-1 antibody (also blocks M2 polarisation)
Polarise to M1 phenotype
- pro-inflammatory IFNγ
- activate bacterial pattern recognition receptor through Toll-like receptors
- anti-IL-10 antibody
Deplete macrophages by chemotherapy

Question 18

Macrophage Origin Associated with Pathology

Answer 18

Adipose tissue-associated macrophages:
- functions: metabolism, adipogenesis, adaptive thermogenesis
- pathology: obesity, diabetes, loss of adaptive thermogenesis
Intestinal macrophages:
- functions: tolerance to microbiota, defence against pathogens, intestinal homeostasis
- pathology: inflammatory bowel disease
Healing macrophages:
- functions: branched morphology, angiogenesis
- pathology: cancer, fibrosis, epithelial hyperplasia