Immunity- part 2 ! ( 2 LOD)

Question 1

What is the Innate immune response and the innate immune system?

Answer 1

> It is the same response for any pathogen
There is no immunological memory
The innate immune system must be able to distinguish self from non-self , to make sure it only acts against foreign pathogens

Question 2

When does the second line of defence come into action?

Answer 2

> Comes into action when pathogens have entered the tissue or the bloodstream

Question 3

What does the innate immune system rely on?

Answer 3

> It relies on the recognition of particular types of molecules that are common to many pathogens.
These pathogen-associated molecules ( called pathogen-associated molecular pattern) stimulate to types of innate immune responses

Question 4

What two innate immune responses do pathogen-associated molecules stimulate?

Answer 4

> Inflammation and phagocytosis by cells: such as dendritic cells, neutrophils and macrophages

Question 5

Overall components of the second line of defence

Answer 5

> White Blood Cells:
—–Phagocytes (Dendritic cells, Neutrophils, Macrophages)
—–NK Cells, Mast Cells and Eosinphills
Soluble proteins: Cytokines, Complement proteins
Inflammation: Fever and inflammation

Question 6

Cells involved In Innate Immunity

Answer 6

> Many types of white blood cells ( immune cells) and leukocytes that protect the body
—–> Found in the blood, lymph and other tissues/sites of infections
—–> Innate leukocytes include NK cells, mast cells, eosinophils and phagocytic cells (macrophages, neutrophils and dendritic cells)

Question 7

Phagocytes or Phagocytic cells

Answer 7

> Cells that engulf and destroy foreign material

Question 8

Phagocytosis

Answer 8

> Phagocytosis is the engulfment and destruction of a pathogen or cellular debris.
Some phagocytes move to the site of infection via inflammation via blood, while others stay in tissue fluid for pathogens.

Question 9

What is APC?

Answer 9

> Macrophages and dendritic cells are also able to activate the immune system and are often referred to as antigen-presenting cells ( APC)

Question 10

Steps in Phagocytosis

Answer 10

> Pathogen is identified by a pattern recognition receptor (PRR) and engulfed by out-foldings of the plasma membrane of the phagocyte
The pathogen is engulfed in a vesicle called a phagosome
Lysosome fuses with the phagosome ( forming a phagolysosome)
Toxic chemicals from the lysosome (including free radicals, lysozymes and proteases) digest and destroy the pathogen.
Indigestible material is discharged from the phagocytic cell by a process by a process of exocytosis

Question 11

Macrophages

Answer 11

> Engulf bacteria and microorganisms, secrete complement proteins and cytokines
Work to destroy pathogens and cellular debris by phagocytosis
Macrophages are mature forms of monocytes
They are large phagocytic cells and are abundant in lymph nodes and peripheral tissues

Question 12

Monocytes

Answer 12

> Produced by stem cells in the bone marrow
Undergo differentiation to become macrophages and settle into the body tissues

Question 13

Neutrophils

Answer 13

> The most abundant white blood cells of the immune system & circulate in the bloodstream
They are phagocytes and they ingest and destroy viruses and microorganisms (bacteria). They also self-destruct after engulfing the bacteria
They are mobile and can move to the site of infection by squeezing between capillary cells

Question 14

Dendritic Cells

Answer 14

> Can engulf pathogens and present their antigens on their surface
They act to activate the adaptive immune response. They reside in and patrol the skin and mucosal surface.
They can migrate to the lymph nodes, leading to the activation of T cells responses to provide a cell-mediated immunity against microbial pathogens

Question 15

Eosinophils

Answer 15

> Present in the respiratory, gastrointestinal and urinary tracts
Assist in defencing against larger parasitic agents that are too large to be engulfed by phagocytosis
Antigen Presentation
Release cytokines and histamine

Question 16

Natural Killer Cells ( NK cells)

Answer 16

> NK cells eliminate intracellular pathogens which innate immune cells cannot attack
NK Cells are lymphocytes that do not affect extracellular pathogens. Instead, they destroy virus-infected cells as well as cancerous cells which both cells often have abnormal or missing MHC markers.

Question 17

Why is killing virus-infected cells by apoptosis (planned) rather than by lysis ( bursting) important?

Answer 17

> Lysis of a virus-infected cell simply explodes the cell, releasing the virus particles into the extracellular fluid so that the virus particles can infect other cells.
Apoptosis destroys both the cell and any viruses it contains in a systematic manner, preventing the further spread of the virus. They release toxins which lyse target cells (no phagocytosis)

Question 18

How do natural killer cells destroy virus-infected cells ?

Answer 18

> NK cells undergo Degranulation (emptying the toxic molecules in granules) or (the release of anti-microbial and toxic molecules from the membrane-bound organelles stored in the cytoplasm of some innate immune cells.
The granules in NK cells contain active protease enzymes known as granzymes and a pore-forming protein called perforin

Question 19

Perforin?

Answer 19

> Perforin molecules form a ring structure that punches a hole in the plasma membrane of the target cells, enabling entry of the proteases (granzymes) into the target cell
Once inside the cytoplasm of the targeted cell, the proteases ( usually granzyme B) induce apoptosis

Question 20

Mast cells

Answer 20

> Mast cells intervene in inflammatory responses
Found in tissue and act very early in the infection by a pathogen
Mast cells contain various chemical granules, including cytokines, histamine and heparin –> This causes histamine and heparin to be released into tissues
Mast cells increase vascular permeability

Question 21

What do histamine, cytokines and heparin do?

Answer 21

> Histamine: Leads to the increased permeability of blood vessels and causes smooth muscles to contract
Cytokines: Attracts other immune cells to the site of the infection
Heparin: Also linked to inflammation, initiating the production of a hormone Bradykinin which contributes to the inflammation associated with mast cells

Question 22

What can inappropriate activation of mast cells and release of histamine lead to?

Answer 22

> Allergic reactions and hypersensitivity

Question 23

First exposure to an Allergen

Answer 23

> Potential allergens, such as antigens on airborne pollen cells, are inhaled, consumed
Cells of the immune system identify this antigen as non-self and an immune response is activated
The production of specific antibodies against the particular allergen occurs. These are immunoglobulin E antibodies (produced by B cells in the tissue around the site of entry of the allergen.
Immunoglobulin antibodies attach to the surface receptors of mast cells that are located in the linings throughout the body (airways). Mast cells that are coated with Immunoglobulin antibodies are said to be primed or sensitised.
The presence of primed mast cells that the person is now sensitised to that particular allergen so that the next exposure will cause an allergic response

Question 24

Allergen reaction: Second exposure!

Answer 24

> When the next exposure to the particular allergen occurs, the Immunoglobulin (IgE) antibodies on the primed mast cells recognise the allergen and bind to it.
The binding of the allergen to the IgE antibodies on the mast cells activates them and they degranulate, releasing their contents of chemical mediators, including histamine
The release of histamine results in the effects of inflammation: an increased blood flow to the region, increased permeability of blood vessels, sneezing, and coughing. etc
Migration of more immune cells continues the inflammatory response. Mast cells

Question 25

Humoral Innate Immunity

Answer 25

> Humoral component of the Immune system involves the action of soluble proteins and their derivatives in extracellular body fluids such as lymph and blood.

Question 26

Opsonisation

Answer 26

Coating of the surface of pathogen cells by complement proteins, makes the pathogens more susceptible to phagocytosis.

Question 27

Chemotaxis

Answer 27

Movement of a cell or organism in response to a chemical stimulus. Small complement peptides that diffuse from the pathogen surface act as chemical signals, attracting immune cells involved in the inflammatory response to the site of the infection.

Question 28

Lysis of pathogens

Answer 28

Some complement proteins are involved in the direct ‘explosive’ killing of extracellular pathogens. This occurs when a membrane-attack complex (MAC) forms on the plasma membrane of the pathogen due to the interaction of various complement proteins.

Question 29

Cytokines

Answer 29

> Are small protein signalling molecules.
Produced by certain T cells in response to cell damage or the presence of a pathogen