Lesson 2

Question 1

Which are the features of the anatomical barriers (innate immunity)?

Answer 1

• resistence to traumas
• elasticity
• impermeability
• self-renewing
• ability of responding to mechanical stress
• ability of reacting to UV radiation
• intrinsic anti-microbial activity: thanks to chemical barriers

Question 2

Chemical barriers: which are the anti-microbial molecules?

Answer 2

lysozyme, cathelicidin, pentraxine, cytokines, chemokines,

Question 3

Lysozyme: what is it? which is its role? Where can we find it?

Answer 3

it’s an ezyme able to break the peptidoglycan component of the cell wall of bacteria (especially gram+). It hydrolyze the 1-4 glycosidic bond connecting N-acetilmuramic and N-acetylglucosamine.
Lysozyme is contained in saliva, granules of granulocytes and monocytes, epithelial tissues, tears, milk.
It can be produced by the Paneth cells (epithelial cells present in the gastrointestinal tract).

Question 4

Cathelicidine: what is it? which is its role? Where an why is it produced?

Answer 4

small peptides that kill the bacteria by destroying their lipoprotein membrane.
It’s produced as a precursor and cleaved into 2 active molecules when requested.
The production and the activation starts thanks to a cytokines’ signal

Question 5

Pentraxin’s features

Answer 5

It’s a family of pattern recognition molecules able to activate innate response.
They can be dividend into short chain and long chain (ex: PTX3)

Question 6

What can we find in the mucosa of lips and mouth?

Answer 6

thinner coerneum layes with serous an mucus gland (they contain the chemical substances able to kill the pathogen), there are also innate lymphocytes

Question 7

Descrive the bronchial mucosa

Answer 7

No corneal layer but there’s a mucus layer produced by the serous mucus gland. The mucus contains lysozyme, cathelicidine and other anti-microbial molecules.
There are dendritic cells, innate lymphocytes and mast cells

Question 8

Structure of the digestive tract mucosae

Answer 8

no ciliated cells, there’re Goblet cells, which produce the mucus (a little less), and Paneth cells, which produce anti-microbials.
This structure is characterized by some invaginations, in order to increase the surface of absorption.
Because of the presence of the microbiome in the intestine, this kind of mucosa is enriched by lymphoid tissue (Mucosa-associated lymphoid tissue = MALT).
There are also macrophages, plasma cells, some B-cells, lymphocytes in the MALT.

Question 9

Defensine: production and role

Answer 9

Paneth cells and neutrophils are involved in the production of defensin: small peptides that can be α or β. They’re able to lyse any kind of pathogen by interfering with the molecules of the bacteria wall or the proteins outside the virus.
Defensin is also important for the maintenance of the intestinal microbiome in order to maintain the homeostasis.

Question 10

Which is the structure of the rectal mucosa?

Answer 10

It has a thin corneum stratum and some lymphoid tissue. The most abundant cells are the Langerhans cells.

Question 11

Which are the difference and the similarity between the epithelium of the penis and the one of the vagina?

Answer 11

the penis is characterized by a corneal layer, whereas the vagina is provided with a mucous layer. In both cases, the epithelium is enriched by residential innate cells (Langerhans cells, macrophages) and less lymphocytes than the other types of mucosae.

Question 12

A bacteria reach a lesion in the ephitelium and start to invade the organism. What happens (generally)?

Answer 12

1- Humoral response: there’s the secretion of alarmines or cytokines that activate the residential innate cells, which may control the invasion by releasing other factors, allowing the healing of the damage.
2- Inflammation signals
3- recruitment and extravasation of the circulating cells

Question 13

How can a cell extravasate?

Answer 13

The extravasating cells reach the site of infection thanks to other inflammatory mediators, like the cytokines and the chemokines. These are released creating a gradient: the most abundant mediators are located close to the damage cells, whereas they’re less present nearby the vessels. Thanks to this gradient, these mediators are able to recruit the requested cells (chemoattraction).

Question 14

Which are the mediators synthetized inside the granules of basophils and mast cells?

Answer 14

• Constitutively present: histamine, heparine, serotonin… They’re immediately released
• Synthesized after few minutes after the degranulation of the first granules: prostaglandins.
  They have to recruit
• Mediator synthetized hours after activation: cytokines and chemokines, that recruit the proper cells needed to fight against the pathogen. They’re called “later mediators” because they need the transcription of new genes

Question 15

Which are the effects of the mediators released by basophils and mast cells?

Answer 15

• Activation of endothelial cells
• Increase of vascular permeability
• Anticoagulant activity
• Attraction of neutrophils, eosinophils and monocytes (innate cells)
• Increased bone marrow production of neutrophils, eosinophils and monocytes. In addition to that, basophils and eosinophils aren’t abundant in the circulation, that why the bone marrow production must be increased when these cells are required
• Smooth muscle contraction
• Bronchoconstriction and increase of mucus secretion, to capture and block the pathogens
• Creation of a toxic environment for microbes and parasites

Question 16

Where can we find basophils and mast cells?

Answer 16

Mast cells are present in the tissues while the basophils are mostly in the circulation.

Question 17

How can we distinguish mast cell and basophils?

Answer 17

The nucleus of the basophils is bilobed while in the mast cell is rounded

Question 18

How can we recognize a neutrophils?

Answer 18

They’re characterized by a polylobate nucleus and contain granules

Question 19

Which are the functions of neutrophils?

Answer 19

• Sentinel activity: they’re in the blood so they’re able to monitor everything
• Phagocytosis: the plasmatic membrane invaginates and envelops the pathogen thanks to receptors. The phagosome is formed is then fused with all the granules inside the neutrophil and all the content inside them start to degrade the pathogen.
  The materials obtained from this process will be then discarded by exocytosis (in this way, each neutrophil is able to phagocyte a lot of pathogens, because all the material doesn’t interfere with the life of the cell)
• Spiderman effect: is due to the ability of neutrophils to release a net which can trap the bacteria. The nucleus releases the DNA, through this release also the cytosolic factor (enzymes of the granules) stick to the DNA.
  Thanks to this net, the bacteria may be trapped and the enzymes kills the factor.
  However, after this effect the neutrophil dies. After its action, the net is removed from the area, otherwise it could lead to the production of antibodies against these molecules (the innate and adaptive responses would be induced against self-components and it can provoke autoimmune diseases).
• Kamikaze effect: after a couple of days outside of the circulation, they die together with the pathogen, their lifespan inside the circulation, on the other hand, lasts about 5-6 days

Question 20

Which are the effects of the activation of neutrophils?

Answer 20

• Rapidly killing of invading microbes
• Establishment of a toxic environment for microbes, parasites and normal and neoplastic host cells
• Activation of endothelial cells: increase in the expression of adhesion molecules, WBC (white blood cells) extravasation
• Chemoattraction of immune cells
• Enhancement of Complex activity (Properdin, which is a component contained inside the granules and it stabilizes the components of the complement on the wall of the bacteria or parasites)
• Massive death of neutrophils, dead pathogens and damaged host cells are responsible for Pus formation (because they are killed together with the pathogen)

Question 21

How can we distinguish a Eosinophil?

Answer 21

They’re also granulocytes, whose granules can by histologically stained by using acid solutions (they become red).

Question 22

Which are the functions of the eosinophils?

Answer 22

• Phagocytosis of microbes and small particles
• When they degranulate, the eosinophils destroy the intruders as well damage of invaded tissue
• Secretion of cytokines, enzymes and anti-microbial proteins and peptides
• Antigen presentation
• Anti-helminthic activity (against worm): they produce the major basic protein, an enzyme that destroy worm’s wall
• Anti-tumor activity: in some kind of tumor they can accumulate and secrete the usual enzyme to kill the tumor cells

Question 23

How can we distinguish a monocyte?

Answer 23

They’re quite small with a bilobated nucleus and have no granules.

Question 24

What are the tissues’ macrophage?

Answer 24

They’re big monocytes rich on internal organelles and characterized by a long lifespan.
They have different functions:
- Professional phagocytosis and subsequent killing of microbes: not only the receptor-mediated one, they also do endocytosis and macropinocytosis
- Scavenger function: they remove old red blood cells
- After clearing all the debris, they also secrete some factors that immediately start the tissue-repair process
- Secretion of cytokines and enzymes to kill the pathogen
- As the neutrophils, they produce (because they are provided with the NAD oxidase and the myeloperoxidase) reactive oxygen species and other radical species, which are toxic for the bacteria
- They’re antigen-presenting cells (especially the dendritic cells)

Question 25

What are the dendritic cells?

Answer 25

They’re very similar to the macrophages, however they’re characterized by an irregular membrane, which forms plastic dendrites. There are different types of DC, deriving from the monocytes (myeloid progenitors) and lymphoid progenitors:
- Conventional dendritic cells (immature): they’re able to phagocytose
o Conventional (es: resident cells like Langerhans)
o Plasmacytoid: produces interferon
- Mature dendritic cells: they’re the professional antigen presenting cells

Question 26

How can we activate a natural killer cell?

Answer 26

Activating and inhibitory receptors on NK belongs to 3 families:
- NCR: natural cytotoxicity receptor
- NKG2: natural killer-group
- KIR: killer Ig-like receptors

Question 27

What is the “missing self”?

Answer 27

It’s a phenomenon that interes NK cells: they’re activated by the absence of the MHC

Question 28

What does the activating receptor of NK cells recognize?

Answer 28

• Stress ligands present in abnormal cells
• Neoplastic cells
• Cells infected by viruses, especially by Cytomegalovirus or the Herpes Virus (itdecrease on the expression of HLA);
• Cells infected by intracellular bacteria: they cause stress in our cells
• Cells covered by antibodies: ADCC (Antibody dependet cellular cytotoxicity)

Question 29

what’s it about the antibody dependent cellular cytotoxicity?

Answer 29

It’s a penomenom of NK cells. the antibody recognizes the viral or bacterial protein and cover all the surface of the target cells.
IgG can be recognized by the NK cells causing the killing of the pathogen.
The antibodies are the bridge between the target and the NK cells.
NK cells release perforin (create pore in the target membrane) and granzymes (proteases that induces apoptosis in the target cells.
Another way to kill is with lytic granules.

Question 30

Examples of cytokines able to activate NK cells?

Answer 30

• IL2: increases lytic activity (increases the transcription for perforin and granzymes)
• IL4: decreases lytic activity to switch off NK cell activity
• IL12: increase the cytokine release
• IL15: increases the proliferation on NK cells
• GM-CSF: induce the bone marrow to produce neutrophils, eosinophils and monocytes

Question 31

Where can we find innate lymphoid cells?

Answer 31

They