L3 + L4: Innate immune cells

Question 1

3 important functions of phagocytes

Answer 1

Clearance of pathogens
Pattern recognition
Phagocytosis (= a cellular process for ingesting and eliminating particles larger than 0.5 um diameter).

Question 2

3 functions of neutrophils

Answer 2

Swallow microbes
Secretion of anti-microbials
Formation of NETs

Question 3

What are the most abundant type of granulocytes? When is the peak of these cells?

Answer 3

Neutrophils make up to 40-70% of all white blood cells. They have a fast response; peak within 3 days.

Question 4

What are NETs?

Answer 4

A network of extracellulair fibers which bind pathogens. It consists of DNA material (from the nucleus of neutrophils) and danger signals (DAMPs).

Question 5

2 downstream effects of NETs

Answer 5

1. Fibrosis on biomaterials; there are a lot of danger signals, this triggers inflammation (result: pro-inflammatory phenotype, increase fibrotic encapsulation, decrease tissue integration).
2. Thrombosis on biomaterial; components in the nets leads to blood clotting.

Question 6

There are two types of NETosis: suicidal NETosis and vital NETosis. Explain how it works.

Answer 6

Suicidal NETosis= slow cell death. Nuclear delobulation and disassembly of nuclear envelope –> cellular depolarization and chromatic condensation –> plasma membrane rupture and release of NETs.

Vital NETosis= rapid release from live cells. Degranulation and expulsion of nuclear chromatin –> extracellular assembly of NET.

The choice of (bio)materials is important for triggering NETosis!!

Question 7

Where do macrophages come from and where do they go to? When are they macropages

Answer 7

Macrophages come from the BM (through monocytes!). They circulate in the blood and in tissues. They go to different places and have different names & functions there; Longs: alveolar macrophages - play a role during COVID. Liver: Kupffer cells - remove alcohol etc. Function dependent on local stimuli/ environment!

From the blood, they go to the wounded tissue and there they become macrophages.

Question 8

What are the two types of macrophages?
Pro-inflammatory?
Stimulated by?
What type of energy?

Answer 8

M1: pro-inflammatory.
Stimulated by: IFN-y, NETs, TNF.
Fast energy (aerobic glycosis)

M2: repair & resolution.
Stimulated by: IL-4, IL-10.
Sustained energy (fatty acid oxidation)

Question 9

What are the 3 phases that macrophages can have?

Answer 9

Pro-repair; stimulate ECM formation
Pro-inflammatory; maintian inflammation
Regulation; stop inflammation

Question 10

Give 2 characteristics of tumor-associated macrophages (TAMs)

Answer 10

Promote angiogenesis –> to feed the tumor
Inhibit inflammation –> prevent immune attack

Question 11

What is the result inflammasome in the FBR?

Answer 11

It is an assembly of 3 components. It promotes proteolytic cleavage, maturation, and secretion of pro-inflammatory cytokines IL-1b and IL-18.

Question 12

What are the two ways that inflammasome occur? Give an example.

Answer 12

1. From the outside of the cell. There are PRR receptors that recognize bacteria. This leads to transcription in the nucleus.
2. From the inside of the cell. Wear particles invade the cell (they are eaten up), but can be dangerous (damage the cell from the inside). Receptors recognize the danger signals. This leads to an inflammatory reaction.

Example: loose implants > wear particles > inflammasome > IL-1b > mature osteoclasts > increased bone resorption > implant failure.

Question 13

What happens when an implant is implanted?
Neutrophils;
Macropages;

Answer 13

Neutrophils;
Oxydative burst (may cause damage in the beginning and die)
Inflammation –> macrophage reqruitement
NET coating –> DAMPs, degradation
Inflammasome –> IL-1b, IL-18

Macrophages;
Polarization state –> degradation, tissue formation, regulation
Antigen presentation –> Thelper cells
Inflammasome –> IL-1b, IL-18

Question 14

Trained immunity =
Give an example.

Answer 14

Trained immunity has been demonstrated to non-specific train innate immune cells (e.g. monocytes and NK cells) against pathogens. It involves epigenetic and metabolic reprogramming of the cells.

Example: Study by Farly et al. Vaccine for tuberculosis (BCG). Mortality ratio vs non-vaccinated: 0.55. Success! But.. only 2% of the children got tuberculosis. So, maybe there is a non-specific effect? This is called trained immunity. A lot of these children have a poor health care system. They die from easy diseases. These vaccines stimulated the immune system. This made them more protected from all kinds of diseases.

Question 15

Macropohage polarization can be matimulated by the … and … and …

Answer 15

Biochemical environment (cytokines, GF, DAMPs/PAMPs)
Physical (micro)environment (stiffness, microstructure)
Mechanical environment (shear flow, cyclic stretch)

Question 16

Pore size and stiffness increase –> M2/M1 decrease or increase? –> more or less inflammation?

Answer 16

Pore size increase –> M2/M1 increase? –> more inflammation?

Question 17

How do macrophages feel their environment?

Answer 17

Via macrophage migration nodes. There are two types: amoeboid migration mode & mesenchymal migration mode.

Question 18

Main difference between amoeboid migration mode and mesenchymal migration mode?

Answer 18

Amoeboid is adhesion-independent (so not environment).

Mesenchymal is adhesion-dependent (depends on the environment).

The mesenchymal mode is characterized by slow migration speed and ECM degradation, while cells in amoeboid mode move fast and do not degrade the ECM.

Question 19

What is amoeboid migration mode?

Answer 19

Via this macrophages can sense their environemt. This is adhesion-independent ((although contact is required) so not depending on the environment). They wiggle their way through.

Cell polarisation –> trailing uropods.
Lack of proteolytic degradation & integrins.
Used by lymphocytes, monocytes, DCs.

Question 20

What is mesenchymal migration mode?

Answer 20

This is what a snail uses to sense its environment (things poking out). It is adhesion-dependent (depends on the environment).

Cell polarisation –> leading pseudopods that interact with the environment via integrins.
Important for this is proteolytic degradation.
Used by fibroblasts, tumor cells, macrophages.

Question 21

What are podosomes?

Answer 21

The things that stick out. Used by cells to ‘feel’.
It consists of actine core + focal adhesion components.
Podosomes can also do: ECM degradation.
They are highly dynamic (stick out, move, go back, etc.)

Question 22

M1 = pro- or anti-inflammatory? M2?

Answer 22

M1: pro
M2: anti

Question 23

Explain how macrophage fusion works.

Answer 23

Fusion starts with IL-4 and IL-13 stimulation. This triggers a pathway. The other trigger is cell-cell contact. You get a macrophage that is fusion-competent. This fusion-competent macrophage has to find another fusion-competent macrophage. They form a bridge and fuse together. Important: protrusion. They start to poke eachotehr with podosomes and more bridges are formed in the fuse.

Question 24

What happens if you disrupt the podosomes (e.g. with compounds) before macrophage fusion?

Answer 24

The macrophages cannot poke eachter > the cells cannot fuse properly.