Introduction ot immunity

Question 1

What is immunity?

Answer 1

Immunity is the ability of an organism to defend itself against infectious agents, foreign cells and proteins, as well as catastrophic cell dysfunction such as cancer.

Question 2

What is immunodeficiency?

Answer 2

Immunodeficiency is the outcome of failed immunity and can be caused by genetic inheritance (e.g., severe combined immune deficiency or SCID) or acquired during life (e.g., acquired immune deficiency syndrome or AIDS).

Question 3

What is an allergy?

Answer 3

Allergy results from the immune system responding inappropriately to antigens.

Question 4

What is hypersensitivity?

Answer 4

Hypersensitivity is another term that describes the immune system’s exaggerated or excessive response to antigens.

Question 5

What is immune tolerance?

Answer 5

Immune tolerance refers to a state of immunological non-reactivity to an antigen, where the immune system does not mount an immune response against it.

Question 6

What are examples of harmless antigens?

Answer 6

Harmless antigens include our cells and tissues (self-antigens), harmless environmental antigens like food sources and pollen, and commensal organisms like skin and gut flora.

Question 7

What happens when there is a breakdown of tolerance?

Answer 7

A breakdown of tolerance occurs when the immune system mounts an immune response against self-tissues, leading to autoimmune diseases.

Question 8

What is the role of innate immunity?

Answer 8

Innate immunity responds rapidly to infection, providing immediate defence against pathogens. However, it cannot adapt and sometimes fail to effectively eliminate the infection.

Question 9

What is the role of adaptive immunity?

Answer 9

Adaptive immunity takes time but it can recognise and respond to various antigens. It provides a specific and tailored response to pathogens.

Question 10

What is the advantage of adaptive immunity?

Answer 10

Adaptive immunity exhibits a memory function, which means that once it encounters a pathogen, it “remembers” it. If the same pathogen is encountered again later in life, the adaptive immune response kicks in quickly and is more effective at eliminating the pathogen.

Question 11

What is the role of the skin in innate immunity?

Answer 11

The skin acts as a physical barrier impermeable to most infectious pathogens, preventing their entry into the body.

Question 12

What is the role of lysozyme in innate immunity?

Answer 12

Lysozyme is an enzyme that breaks down glycosidic bonds in bacterial cell walls, assisting in the destruction of bacteria.

Question 13

How does mucus contribute to innate immunity?

Answer 13

Mucus traps pathogens, preventing their movement and spread. Epithelial cell cilia then expel the trapped pathogens from the body.

Question 14

How do low stomach pH and digestive enzymes contribute to innate immunity?

Answer 14

The low pH of the stomach and the presence of digestive enzymes create an uninhabitable environment for pathogens, preventing their survival and growth.

Question 15

What is the role of intestinal flora in innate immunity?

Answer 15

Intestinal flora (microorganisms) in the gut and vagina help antagonise infections from external pathogens, promoting a healthy microbial balance and preventing the overgrowth of harmful organisms.

Question 16

What is the role of red bone marrow in the immune system?

Answer 16

Red bone marrow serves as the site of production for all blood cells, including B and T lymphocytes, which are important immune system components.

Question 17

What are lymph nodes and their role in the immune system?

Answer 17

Lymph nodes are small, egg-shaped or round structures in lymphatic vessels. They contain resident lymphocytes and macrophages, which neutralise pathogens and clear debris. During infection, lymph nodes can become enlarged.

Question 18

What is the function of the spleen in the immune system?

Answer 18

The spleen acts as an “emergency” blood store and also cleans the blood of pathogens and debris.

Question 19

What is the role of the thymus in the immune system?

Answer 19

T-lymphocytes undergo maturation in the thymus, preparing them for their role in the immune response.

Question 20

What are leukocytes?

Answer 20

Leukocytes, also known as white blood cells, are a group of cells involved in the immune response.

Question 21

What is the function of macrophages?

Answer 21

Macrophages are phagocytic cells that are highly migratory and also serve as professional antigen-presenting cells, playing a crucial role in the immune response.

Question 22

What is the function of neutrophils?

Answer 22

Neutrophils are highly abundant and migratory cells that coordinate the inflammatory response, playing a key role in defending against infections.

Question 23

What is the function of eosinophils?

Answer 23

Eosinophils are involved in host defence against nematodes and other parasites, playing a role in immune responses related to parasitic infections.

Question 24

What is the function of basophils?

Answer 24

Basophils are involved in host defences against multicellular parasites, participating in immune responses against parasitic infections.

Question 25

What is the function of dendritic cells?

Answer 25

Dendritic cells are the most adept antigen-presenting cells, specialising in capturing and presenting antigens to other immune cells, thus initiating and shaping immune responses.

Question 26

What is the function of B cells?

Answer 26

B cells are adaptive immune cells that produce antibodies that bind to antigens on pathogens. They play a crucial role in humoral immunity and exhibit immunological memory, providing long-term protection against specific pathogens.

Question 27

What is the function of T cells?

Answer 27

T cells are adaptive immune cells that have multiple functions. They are involved in killing virus-infected cells through cytotoxic activity. Additionally, T cells are key in coordinating immune responses and are responsible for activating and terminating immune reactions. They are considered the orchestrators of the immune system.

Question 28

How do B and T cells participate in constant surveillance for invading pathogens?

Answer 28

B and T cells continually circulate the blood and lymphatic systems, scanning for invading pathogens and other foreign substances.

Question 29

What are High Endothelial Venules (HEVs)?

Answer 29

High Endothelial Venules (HEVs) are specialised sites in lymph nodes where lymphocytes, including B and T cells, cross from the blood circulation into the lymphatic system.

Question 30

Can B cells access all areas of the body?

Answer 30

Yes, B cells can access all areas of the body. They are not restricted to specific locations and can migrate to different tissues and organs in response to infection or immune activation.

Question 31

Are antibodies produced by B cells restricted to the bloodstream?

Answer 31

No, antibodies produced by B cells are not restricted to the bloodstream. Once produced, antibodies, including the lymphatic system and various tissues, can travel throughout the body to help neutralize pathogens and eliminate infections.

Question 32

What is the purpose of lymphocyte recirculation?

Answer 32

The process of continual lymphocyte recirculation allows a maximum number of antigenically committed lymphocytes to encounter and interact with antigens, enhancing the immune response.

Question 33

How frequently does an individual lymphocyte make a complete circuit around the system?

Answer 33

An individual lymphocyte can make a complete circuit around the system approximately 1 to 2 times a day.

Question 34

Why is it important for lymphocytes to travel widely in the body?

Answer 34

Approximately 1 in 100,000 lymphocytes will bind to a specific antigen. To increase the chances of encountering and detecting the presence of antigens, it is essential for each lymphocyte to travel widely throughout the body.

Question 35

What is the requirement for a lymphocyte to enter inflamed tissue or peripheral lymphoid organs?

Answer 35

Before a lymphocyte can enter inflamed tissue or peripheral lymphoid organs, it must adhere to and penetrate the layer of endothelial cells lining the walls of blood vessels, a process known as extravasation.

Question 36

What do pattern recognition receptors (PRRs) do in innate immunity?

Answer 36

Pattern recognition receptors (PRRs) in innate immunity detect antigens non-specifically using receptors for Pathogen-Associated Molecular Patterns (PAMPs).

Question 37

What are examples of PRRs?

Answer 37

Examples of PRRs include a large family known as the Toll-like receptors (TLRs), which play a crucial role in recognizing and responding to PAMPs.

Question 38

What are PAMPs?

Answer 38

PAMPs are molecular structures in lower organisms, such as bacteria and fungi, but not humans. They are recognized by PRRs and serve as molecular patterns indicating the presence of pathogens.

Question 39

Can you provide examples of PAMPs?

Answer 39

Examples of PAMPs include lipopolysaccharides found in the outer membrane of bacteria and peptidoglycans found abundantly on the bacterial cell wall. These PAMPs are recognized by PRRs, triggering innate immune responses.

Question 40

How is phagocytosis triggered?

Answer 40

Phagocytosis is triggered by receptor cross-linking, which occurs when antigens bind to multiple receptors on the surface of the phagocytic cell.

Question 41

What happens when receptors on the phagocytic cell are cross-linked?

Answer 41

The intracellular domains of the receptors on the phagocytic cell are associated with protein enzymes capable of phosphorylating others of their kind. Normally, the membrane structure keeps these signaling domains spatially apart. However, antigen-mediated cross-linking brings the receptor complexes closer, allowing phosphorylation.

Question 42

What is the result of receptor cross-linking and phosphorylation?

Answer 42

Receptor cross-linking and phosphorylation trigger a signal transduction pathway within the phagocytic cell. This pathway leads to the activation of downstream cellular processes, ultimately resulting in phagocytosis of the targeted particles or pathogens.

Question 43

What do pattern recognition receptors (PRRs) bind to?

Answer 43

PRRs bind to a limited array of pathogen-associated molecular patterns (PAMPs) that can be protein, carbohydrate, or lipid-based.

Question 44

What do adaptive immune response receptors bind to?

Answer 44

Adaptive immune response receptors can bind to a potentially infinite array of pathogen-associated peptides, which are usually protein-based for T cells and occasionally carbohydrates or lipids for B cells.

Question 45

Do pattern recognition receptors exhibit molecular memory or the ability to improve/adapt during an immune response?

Answer 45

No, PRRs do not exhibit molecular memory or the ability to improve/adapt during an immune response. They provide a non-specific, immediate response to recognize and initiate defense against pathogens.

Question 46

Do adaptive immune response receptors exhibit molecular memory and the ability to improve/adapt during an immune response?

Answer 46

Yes, adaptive immune response receptors induce molecular memory and have the ability to improve/adapt during an immune response. This allows for a more specific and tailored response to encountered pathogens.

Question 47

How are the genes encoding pattern recognition receptors and adaptive immune response receptors different?

Answer 47

Genes encoding pattern recognition receptors are entirely germ line encoded, while adaptive immune response receptors undergo gene editing and modification to the genome in somatic immune cells.

Question 48

What are the mechanisms of leukocyte signaling?

Answer 48

Leukocyte signaling involves ligand-receptor interactions, phosphorylation of adapter molecules, and the initiation of gene expression, which collectively regulate various cellular responses.

Question 49

What is the inflammatory response?

Answer 49

The inflammatory response is a complex process that involves the recruitment of immune cells, dilation of blood vessels, increased vascular permeability, and the release of inflammatory mediators. It plays a crucial role in the body’s defense against infection and injury.

Question 50

What are some soluble factors that play a role in immunity?

Answer 50

Complement is a family of plasma proteins that activate each other in a cascade, capable of destabilizing the membranes of invading bacteria and marking them for destruction by antibodies. Lysozyme is a hydrolytic enzyme found in saliva and tears that can destroy the bacterial cell wall. Cytokines, including chemokines that attract cells to the site of infection, are also important in immune responses. An example is interferon, a glycoprotein that interferes with viral replication.

Question 51

How do leukocytes communicate with each other?

Answer 51

Leukocytes communicate using small soluble messaging proteins known as cytokines and chemokines.

Question 52

What is the role of cytokines and chemokines in leukocyte communication?

Answer 52

Cytokines and chemokines bind to receptors on the target cell, triggering signaling transduction cascades. These cascades ultimately lead to gene expression changes, resulting in cell function alterations.

Question 53

What is juxtacrine action in leukocyte communication?

Answer 53

Juxtacrine action is a mode of cell communication that requires direct cell-to-cell contact. It is similar to paracrine action, where cells release signaling molecules into the local environment, but in juxtacrine action, the signaling occurs through direct contact between cells.