Lec 7 and 8 - Innate Immune Cells

Remember the 5 paradigms of the immune system from last lecture? Which will we be focusing on now?

1. Sensing

2. Specialization

3. Reaction

4. Regulation

5. Memory

So we know how cells SEE their targets, but now we’re going to talk about how they …

…how they GET to their targets.

What are the innate immune cells?

• innate lymphoid cells

  • innate lymphoid cell

  • NK cells

• granulocytes

  • neutrophils

  • eosinophil

  • mast cells

  • basophils

• mononuclear phagocytes

  • monocytes

  • macrophages

  • dendritic cells

A neutrophil is a type of [what cell category?]….

…of GRANULOCYTE!

In a neutrophil, what are the sacs you see?

multiple nuclei!

Multiple nuclei AKA

polymorphonuclear

In a basophil, what are all the dots you see?

granules!

A monocyte is a type of [what cell category?]…

.. a mononuclear phagocyte!

T/F: The nucleus of a monocyte is single lobed.

true!

How are immune cells born? Most immune cells come from the…

from the bone marrow!

Most immune cells come from the bone marrow, except for…

…except for sentinel macrophages!

Where do sentinel macrophages come from then if not the bone marrow?

sentinel macrophages in many tissues come from yolk sac/fetal liver.

T/F: So sentinel macrophages only renew through self-replication (not being born).

true!

How are immune cells born? The process is called:

hematopoiesis! the generation of both red and white blood cells

• hemato = blood

• poiesis = generation

Immune cells born in the bone marrow are called ______ stem cells.

Immune cells born in the bone marrow are called Hematopoietic stem cells (HSC cells).

Hematopoietic stem cells (HSC cells) generate immune cells while self-renewing.

….

HSCs are multipotent, meaning they create cells of MANY different types. What is the property of stem cells being able to renew (self replicate) and differentiate/specialize called?

stemness!

What precursor gives rise to adaptive and innate immune lymphocytes?

The Common Lymphoid Precursor (CLP)!

Let’s learn more about the macrophage (a mononuclear phagocyte). What is its origin?

• existing ones in the tissues come from the yolk sac/fetal liver

• those induced by inflammation (those that need to be made in a pinch) come from bone marrow via monocytes

Let’s learn more about the macrophage (a mononuclear phagocyte). Where is it found?

• it’s sentinel in all tissues

• it can be induced from blood via monocytes!

Let’s learn more about the macrophage (a mononuclear phagocyte). What does it do?

• kills pathogens via phagocytosis

• produces cytokines

1. Pattern Recognition Receptor (PRR) recognizes PAMP on bacterial cell

2. Engulfs bacteria into phagosome

3. Fuses into phagolysosome (the lysosomes contain killing products)

4. Signalling cascade via cyto/chemokines

T/F: Macrophage killing via phagocytosis is stronger than neutrophil killing.

FALSE! Neutrophil killing > macrophage killing

What are the granule products of a macrophage’s killing?

• reactive oxygen species (ROS)

• enzymes (lysozymes, lipases, nucleases, etc)

• acidification

Macrophages produce cytokines. What do these cytokines do when released locally?

Macrophage cytokines released locally will recruit other immune cells towards the infection (chemokines) and activate more potent function in both adaptive + innate immune cells.

Macrophages produce cytokines. What do these cytokines do when released systemically?

Macrophage cytokines released systemically will cause fever and induce more liver-derived proteins like complement, etc.

How do macrophages help maintenance of healthy tissues?

Macrophages clear away dead cell, produce ECM, produce growth factors, support angiogenesis (making of new blood vessels), support wound healing.

What are the 2 types of macrophages?

• M1 = killer macrophages

• M2 = healer macrophages

How do macrophages decide to either specialize into killers (M1) or healers (M2)?

it depends on what cytokines stimulate it!

The act of Cytokine stimulation to turn (ex.) macrophages into either (ex.) killers (M1) or healers (M2) is called:

CYTOKINE POLARIZATION

What do killers (M1) macrophages do?

they have increased capacity to detect and engulf pathogens, and increased products to kill pathogens!

What do healers (M2) macrophages do?

they have increased capacity to detect cellular debris, and increase production of molecules to promote wound healing!

T/F: Macrophages today are considered either killer (M1) or healer (M2).

false! today it’s actually a spectrum between the two!

Let’s learn more about the dendritic cells (a mononuclear phagocyte). What is its origin?

Dendritic cells come from the bone marrow.

Let’s learn more about the dendritic cells (a mononuclear phagocyte). Where does it go?

• dendritic cells are sentinels in all barrier tissues (mucosa, skin)

• they go to lymphoid organs (lymph nodes, spleen)

Let’s learn more about the dendritic cells (a mononuclear phagocyte). What does it do?

activates adaptive immunity!

Dendritic cells act as immune system lookouts that detect danger signals from pathogens (PAMPs) or damage (DAMPs)

Let’s learn more about the dendritic cells (a mononuclear phagocyte). What does it have to have on its surface to activate T cells?

Dendritic cells express MHC, and CD80 & CD86 (co-stimulatory proteins) on their surface ! It binds to T cell receptors to activate T cellls!

CD80 and CD86 (co-stimulatory proteins on the surface of dendritic cells) only turn on when there is danger. Danger as in _________ or __________________.

Danger as in PAMPs (Pathogen-Associated Molecular Patterns) or DAMPs (Damage-Associated Molecular Patterns).

Dendritic cells express MHC, and CD80 & CD86 (co-stimulatory proteins) on their surface ! It binds to T cell receptors to activate T cellls!

The T cells become activated only because the dendritic cell is PRESENTING the proof of infection to the T cell stuck to the [CD80 / CD86 / MHC] molecule.

The T cells become activated only because the dendritic cell is PRESENTING the proof of infection to the T cell stuck to the MHC molecule.

Dendritic cells have activate adaptive immunity when you have an infection etc. But what about when the body is in perfectly healthy homeostasis — how do they they prevent the immune system from attacking your body's own healthy cells?

Immature dendritic cells constantly sample normal self-antigens and display them on MHC molecules (Signal 1), but they express very low or no CD80/CD86 (Signal 2). You need both to activate killer T cells.

Instead the T cell becomes permanently unresponsive/paralyzed and triggers its own apoptosis. The T cell turns into a Regulatory T Cell (Treg), which actively suppresses other immune cells from attacking healthy tissue.

Let’s learn more about the monocytes (a mononuclear phagocyte). What is its origin?

monocytes come from bone marrow!

Let’s learn more about the monocytes (a mononuclear phagocyte). Where do they go?

Monocytes go to the blood and get recruited into tissues during an inflammatory response!

Let’s learn more about the monocytes (a mononuclear phagocyte). What do they do?

• phagocytose!

• differentiate into other cells!

So monocytes differentiate into other cells. They’re basically circulating precursors. What are these cells it turns into?

Monocytes differentiate into macrophages and dendritic cells!

How do monocytes know WHEN to differentiate into macrophages and dendritic cells?

cuz once a monocyte enters a tissue, it follows local cues (cytokines etc and also local context (inflammation, healing, etc)

Ok now let’s learn more about the granulocytes!

…

T/F: Basophil, eosinophil, neutrophil (granulocytes) get their names from blood staining.

true!

Hematoxylin is positively charged, it binds neg / acidic stuff like DNA.

Eosin is negatively charged, it stains pos / basic stuff in cytopasm / connective tissue.

Rem. phil = loving (hydrophilic, pedophilic etc)

…

Let’s learn more about the neutrophils (a granulocyte). What is its origin?

neutrophils come from the bone marrow

Let’s learn more about the neutrophils (a granulocyte). Where do they go?

neutrophils circulate in blood and rapidly get recruited into tissues during inflammation

Let’s learn more about the neutrophils (a granulocyte). What do they do?

neutrophils phagocytosis and NETose!

What is NETosis?

a specialized form of cell death used by neutrophils where they eject their own DNA into the extracellular space to form sticky, web-like structures called Neutrophil Extracellular Traps (NETs) that trap pathogens.

then the pathogen burns to death in the web because of the caustic materials lining the DNA.

T/F: Only neutrophils are capable of NETosis (the web expulsion).

false! other cells do it too but it’s best understood in neutrophils

macrophages - METosis

eosinophil - EETosis

T/F: Neutrophils are not very effective killers.

false!

• neutrophils are VERY effective killers. they express many PRRs (pathogen recognition receptors).

• they also express complement receptors (CR3/CR4) to detect complement on pathogens

• —> potently destroy material that they phagocytose

WHY are neutrophils such strong killers?

cuz neutrophils store toxic molecules in their granules! they have 4 different types of granules with diff molecules inside each (defensins, other AMPs, potent cleaving enzymes, ROS, acidification, lactoferrin to steal iron from pathogens)

T/F: Neutrophils get phagocytosed by macrophage after?

true!

Neutrophils are like the HULK, they’re super crazy violent and reckless. They release tons of very toxic products, create massive nets —> TOO MUCH COLLATERAL DAMAGE.

How are neutrophils regulated?

dont worry, neutrophils have a very short lifespan (5 days) and also die shortly after killing.

also neutrophils only enter healthy tissue after inflammation, not typically there.

Let’s learn more about eosinophils (a granulocyte). What is their origin?

eosinophils come from bone marrow!

Let’s learn more about eosinophils (a granulocyte). Where do they go?

eosinophils circulate in blood and become sentinels in some mucosal tissues (intestine, uterus)

Let’s learn more about eosinophils (a granulocyte). What do they do?

eosinophils kill massive parasites by releasing toxic granules (degranulation)

Eosinophils kill massive parasites by releasing toxic granules (degranulation). Why? Why not just phagocytose (eat) it?

cuz parasites are too big to eat! so instead degranulation helps destroy the outside of the parasite (shoot toxic granules onto the outside of the parasite)

Ok so we know that eosinophils kill parasites via degranulation when there is infection, but what about their role when body is perfectly healthy homestatic?

Eosinophils use their granule products to remodel tissues (granule proteases digest ECM —> allows new deposition —> produces growth factors like VEGF which supports angiogenesis).

they essentially renovate tissues as they constantly wear and tear

T/F: Mice without eosinophils are perfectly fine.

false! Mice without eosinophils have smaller intestinal villi. Resulting in poorer nutrient uptake, and overall worse tissue function.