Innate Immunity

Question 1

Define innate immunity.

Answer 1

Innate immunity is the inborn resistance against infections that an individual possesses right from birth as a result of their genetic makeup, and which is non-specific.

Question 2

What are nine components of innate immunity?

Answer 2

(1) Physical and chemical barriers
(2) Cellular components
(3) Pattern Recognition Receptors (PRRs)
(4) Inflammatory response
(5) Complement system
(6) Antimicrobial proteins and peptides
(7) Cytokines and chemokines
(8) Acute phase response
(9) Interaction with adaptive immunity

Question 3

features of innate immunity

Answer 3

acts in minutes, prior microbial exposure is not required, diversity is limited, it is non-specific, no memory

Question 4

external defenses of innate immunity

Answer 4

skin, mucous membranes, secretions

Question 5

internal defenses of innate immunity

Answer 5

phagocytic cells, antimicrobial proteins, inflammatory responses, natural killer cells

Question 6

functions of innate immunity

Answer 6

➤ recruitment of immune cells: produces chemical signals to attract immune cells to the site of infection.
➤ activation of the complement system: a group of proteins that enhance the ability of antibodies and phagocytic cells to clear microbes and damaged cells.
➤ removal of foreign substances: identifies and eliminates pathogens and debris through phagocytosis.
➤ activation of adaptive immunity: presents antigens to the adaptive immune system to help develop a more specific and long-lasting immune response.

Question 7

Compare innate immunity and adaptive immunity.

Answer 7

➤ Innate immunity: resistance to infection that an individual possess since birth. Adaptive immunity: Resistant to infection that an individual acquires during his lifetime.
➤ Innate immunity: Immune response occurs in minutes. Adaptive immunity: Immune response occurs in days.
➤ Innate immunity: Prior exposure to the antigen is not required. Adaptive immunity: Develops following antigenic exposure.
➤ Innate immunity: Diversity is limited, acts through a restricted set of reactions. Adaptive immunity: More varied and specialized responses.

Question 8

What are the primary phagocytic cells in the innate immune system?

Answer 8

Macrophages and neutrophils.

Question 9

State the role of macrophages and neutrophils in innate immunity.

Answer 9

Macrophages are critical effector cells in innate immunity that engulf and digest pathogens, dead cells, and debris through phagocytosis, and they also secrete cytokines to mediate inflammation and recruit other immune cells.

Neutrophils are the most abundant white blood cells and act as the first responders to infection, rapidly migrating to sites of infection where they kill pathogens through phagocytosis, degranulation, and the release of neutrophil extracellular traps (NETs).

Question 10

Macrophages and neutrophils are both crucial components of the innate immune system. Compare the two using the following criteria:
(a) Origin and development
(b) Location
(c) Lifespan
(d) Morphology
(e) Response to infection
(f) Chemotaxis

Answer 10

(a) Origin and development
Macrophages: Derived from monocytes, which are produced in the bone marrow and circulate in the bloodstream. When monocytes migrate into tissues, they differentiate into macrophages.
Neutrophils: Formed from hematopoietic stem cells in the bone marrow. They undergo several stages of maturation before being released into the bloodstream.

(b) Location:
Macrophages: Found in tissues throughout the body, including the liver (Kupffer cells), lungs (alveolar macrophages), brain (microglia), and skin (Langerhans cells).
Neutrophils: Primarily found in the bloodstream and are among the first cells to migrate to sites of infection.

(c) Lifespan
Macrophages: Long-lived, persisting for weeks to months.
Neutrophils: Short-lived, typically surviving for a few days.

(d) Morphology
Macrophages: Larger cells with a single, kidney-shaped nucleus and lack granules.
Neutrophils: Smaller cells with a multi-lobed nucleus and granular cytoplasm containing enzymes and antimicrobial substances.

(e) Response to infection
Macrophages: Respond more slowly to infection but are crucial for chronic infections and tissue repair.
Neutrophils: Rapid responders to infection, particularly effective against bacteria.

(f) Chemotaxis
Macrophages: Slower chemotactic response compared to neutrophils.
Neutrophils: Rapid chemotactic response, quickly migrating to infection sites.

Question 11

What triggers the activation of macrophages in the initial phase of an immune response?

Answer 11

recognition of pathogens through engagement of PRRs

Question 12

What type of cells are Natural Killer (NK) cells, and what is their role?

Answer 12

NK cells are lymphocytes that target and kill virus-infected cells and tumor cells without prior sensitization.

[5-minute video]: Natural Killer Cells

Question 13

How do dendritic cells bridge innate and adaptive immunity?

Answer 13

They capture antigens from pathogens and present them to T cells, initiating an adaptive immune response.

Question 14

What is the role of mast cells in the immune response?

Answer 14

They release histamine and other mediators to increase blood flow and attract immune cells to infection sites, and are involved in allergic reactions.

Question 15

“Mast cell granules contain, among other factors copious amounts of the vasoactive amino acid histamine.” What can provoke mast cell degranulation?

Answer 15

(a) direct injury
(b) in response to complement components (C3a and C5a)
(c) encounter with PAMPs
(d) binding of IgE to specific mast cell surface receptors

Question 16

What are the roles of eosinophils and basophils in innate immunity?

Answer 16

Eosinophils are effective against parasitic worms, while basophils release histamine and contribute to inflammation and allergic responses.

Question 17

What is the function of monocytes in the immune system?

Answer 17

They circulate in the blood, migrate to tissues, and differentiate into macrophages or dendritic cells. Macrophages are highly effective at phagocytosis and dendritic cells are the most potent antigen-presenting cells.

Question 18

What is the significance of NK cells not requiring prior sensitization?

Answer 18

It allows for a rapid immune response to virus-infected cells and tumor cells.

Question 19

What are PAMPs and PRRs?

Answer 19

Pathogen-Associated Molecular Patterns (PAMPs) are conserved molecular motifs found on pathogens but not on host cells. The include components like lipopolysaccharides (LPS) from gram-negative bacteria, peptidoglycan from gram-positive, and viral RNA.

Pattern Recognition Receptors (PRRs) are proteins on immune cells that detect PAMPs. Examples include Toll-like receptors (TLRs) and NOD-like receptors (NLRs), which trigger immune responses to eliminate the pathogens.

Question 20

What are cytokines?

Answer 20

Cytokines are signaling proteins released by immune cells that regulate the immune response, promoting inflammation, activating immune cells, and directing them to infection sites.

Question 21

What are chemokines?

Answer 21

Chemokines are a subset of cytokines that specifically induce chemotaxis in nearby responsive cells.

Question 22

List some examples of cytokines involved in innate immunity.

Answer 22

Examples include interleukins (IL-1, IL-6), tumor necrosis factor (TNF), and interferons (IFN-α, IFN-β).

Question 23

Define acute phase response.

Answer 23

Acute phase response is a rapid inflammatory reaction triggered by infection or trauma, whereby the liver, stimulated by inflammatory cytokines like IL-1, IL-6, and TNF-α, increases its production of acute phase proteins.

Question 24

Give two examples of acute phase proteins.

Answer 24

mannose-binding lectin, C-reactive protein

Question 25

Acute phase response

What is the role of C-reactive protein?

Answer 25

CRP binds to microbial surfaces and damaged cells, acting as an opsonin to enhance phagocytosis and activating the complement system.

Question 26

Acute phase response

How does mannose-binding lectin (MBL) contribute to innate immunity?

Answer 26

MBL binds to mannose-rich glycans on pathogens, promoting phagocytosis and activating the lectin pathway of the complement system.

Question 27

What are some symptoms that characterize the inflammatory response?

Answer 27

📝 redness of the skin, due to locally increased blood circulation
📝 heat, either increased local temperature, or a systemic fever
📝 swelling of affected tissues
📝 increased production of mucus, which can cause symptoms like a runny nose or a productive cough; * pain, either local pain or affecting the whole body, such as body aches; and
📝 possible dysfunction of the organs or tissues involved

Question 28

What are dendritic cells?

Answer 28

Dendritic cells (DCs) are antigen-presenting cells that process antigen material and present it on their surface to T cells, acting as messengers between the innate and adaptive immune systems.

Question 29

Where are dendritic cells commonly found?

Answer 29

Dendritic cells are commonly found in tissues that are in contact with the external environment, such as the skin, nose, lungs, stomach, and intestines.

Question 30

List the three pathways of the Complement System.

Answer 30

(1) Classical pathway
(2) Lectin pathway
(3) Alternative pathway

Question 31

State three functions of the complement system.

Answer 31

(1) Opsonization: The complement system enhances phagocytosis of antigens by marking them for recognition and ingestion by phagocytes. This process is known as opsonization and is primarily mediated by the complement protein C3b.
(2) Promotion of inflammation: Complement proteins help in promoting inflammation, which serves to limit the spread of infection and attract additional immune cells to the site of infection or injury. Inflammatory responses are facilitated by anaphylatoxins such as C3a and C5a, which are produced during complement activation.
(3) Lysis of pathogens: The complement system can directly lead to the lysis of pathogens through the formation of the membrane attack complex (MAC). The MAC creates pores in the cell membranes of pathogens, causing water and ions to flow into the cells, leading to their destruction.

Question 32

Briefly outline the steps in the process of phagocytosis.

Answer 32

(1) Chemotaxis and adherence of microbe to phagocyte
(2) Ingestion of microbe by phagocyte
(3) Formation of phagosome
(4) Fusion of the phagosome with a lysosome to form a phagolysosome
(5) Digestion of ingested microbeby enzymes
(6) Formation of residual body containing indigestible material
(7) Discharge of waste materials
[Diagram]

Question 33

Identify the immune cells: [Slide].

Answer 33

neutropohils

Question 34

Identify the immune cell: [Slide].

Answer 34

eosinophil

Question 35

Identify the immune cells: [Slide].

Answer 35

basophils

Question 36

Identify the immune cell: [Slide].

Answer 36

monocyte

Question 37

Identify the immune cells: [Slide].

Answer 37

lymphocytes

Question 38

Allergic reactions are frequently associated with an increase in the presence of ____________.
(a) Eosinophils
(b) Neutrophils
(c) Lymphocytes
(d) Basophils
(e) Monocytes

Answer 38

(a) Eosinophils

Question 39

Natural killer (NK) cells have all the following characteristics EXCEPT:
(a) have CD16 receptor
(b) eliminate tumor and virally infected cells
(c) are neither T nor B cells
(d) have specific T cell receptors
(e) have cytotoxic activity

Answer 39

(d) have specific T cell receptors