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CTB Block 2 > B2 W1 - Innate Immunity > Flashcards

B2 W1 - Innate Immunity Flashcards

1
Q

What is the primary function of the immune system?

A

The immune system protects against infectious diseases.

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2
Q

What is an antigen?

A

An antigen is any molecule that can trigger an immune response in both the innate and adaptive immune systems.

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3
Q

Which branch of the immune system provides the first line of defence?

A

The innate immune system is the primary line of defence, offering a more immediate response.

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4
Q

How quickly does the innate immune system respond to a threat?

A
  • Rapid response
  • Typically within hours or a few days.
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5
Q

How long does it take for the adaptive immune response to develop?

A

Usually several days to weeks.

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6
Q

What types of threats does the innate immune system recognise?

A

General molecular patterns commonly found in pathogens, but absent in humans.

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7
Q

How does the adaptive immune system’s recognition abilities differ from the innate system?

A

The adaptive immune system can potentially recognise a vast array of threats, including specific antigens.

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8
Q

Does the innate immune system exhibit memory of past infections?

A
  • No
  • The innate immune system lacks memory.
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9
Q

Why does the adaptive immune system have memory?

A
  • Clonal selection
  • A process where cells that recognise a specific threat are expanded and some are retained as memory cells.
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10
Q

What is the consequence of the adaptive immune system’s memory?

A

Immunological memory allows the adaptive immune system to mount a faster and stronger response upon re-exposure to the same threat.

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11
Q

What characterises the innate immune system’s specificity compared to the adaptive immune system?

A

The innate immune system is non-specific, while the adaptive immune system is highly specific.

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12
Q

How is innate immunity described in terms of its presence and induction?

A

Innate immunity consists of natural defences that are present at birth and do not require prior exposure to a pathogen to become active.

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13
Q

How long does a typical innate immune response last?

A

The innate immune response is relatively short-lived.

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14
Q

What is a potential drawback of the innate immune system’s regulation and amplification?

A

The innate immune system’s response has relatively poor amplification and regulation, which may pose a risk of damaging self-antigens.

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15
Q

From an evolutionary perspective, how is innate immunity viewed?

A

Innate immunity is the more ancient form of immunity, found widely across various species.

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16
Q

What are the three main components of the innate immune system?

A

The three main components of innate immunity are:Physical barriersWhite blood cells (leukocytes)Humoral elements (plasma proteins)

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17
Q

What is the fundamental principle of barrier immunity?

A

Barrier immunity aims to prevent microorganisms from entering the body, or more specifically, from penetrating beyond body cavities and luminal spaces.

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18
Q

What is the body’s primary physical barrier against infection?

A

Skin acts as the primary physical barrier, effectively preventing most infectious agents from entering the body.

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19
Q

Besides the skin, what other physical barriers contribute to innate immunity?

A

Mucous membranes and the mucus they secrete, along with cilia in the respiratory system, also play a crucial role as physical barriers.

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20
Q

What are some examples of ‘biochemical barriers’ in innate immunity?

A

Biochemical barriers include skin secretions, enzymes like lysozyme in tears, stomach acidity, and the presence of commensal organisms.

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21
Q

How do commensal organisms contribute to barrier immunity?

A

The body’s normal microbiome, or commensal organisms, protect against harmful organisms, primarily by competing for resources.

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22
Q

Where do most infectious agents typically enter the body?

A

Most infectious agents enter the body through mucosal surfaces like the nasopharynx, respiratory, gastrointestinal, and genitourinary tracts.

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23
Q

What is the function of mucus on interior epithelial surfaces?

A

Mucus, containing secreted mucins, prevents pathogens from adhering to epithelial surfaces and aids in their clearance by cilia.

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24
Q

What are defensins, and what is their role in barrier immunity?

A

Defensins are peptides found in mucus, such as in the GI tract, that kill or inhibit the growth of pathogens.

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25
Q

How do cilia contribute to barrier immunity in the respiratory system?

A

Cilia help to waft infections out of the lower regions of the respiratory tract, preventing them from reaching the lungs.

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26
Q

Where do most blood cells, including those involved in immunity, originate and develop?

A

Most blood cells develop from stem cells in the bone marrow.

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27
Q

What are the two main lineages of blood cell development?

A

Blood cell development diverges into two main lineages: the common lymphoid progenitor and the common myeloid progenitor.

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28
Q

What are the main types of cells derived from the common lymphoid progenitor?

A

The common lymphoid progenitor gives rise to T cells, B cells, and natural killer (NK) cells.

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29
Q

What are the primary functions of T cells and B cells?

A

T cells and B cells are lymphocytes that form the foundation of the adaptive immune response.

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30
Q

What distinguishes NK cells from T and B cells in terms of their role in immunity?

A

While derived from the lymphoid lineage, NK cells are part of the innate immune system, unlike T and B cells which are part of the adaptive immune system.

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31
Q

What is the role of dendritic cells in the immune system, and from which lineages can they arise?

A

Dendritic cells function in both the innate and adaptive immune responses, primarily by engulfing pathogens and presenting antigens to T cells. They can originate from either lymphoid or myeloid progenitors.

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32
Q

What are the primary cell types that develop from the common myeloid progenitor and contribute to the innate immune response?

A

The common myeloid progenitor gives rise to monocytes, macrophages, neutrophils, eosinophils, basophils, and mast cells, all of which play roles in innate immunity.

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33
Q

What is the function of megakaryocytes and erythrocytes, and how are they related to the immune system?

A

Megakaryocytes produce platelets essential for blood clotting, while erythrocytes are red blood cells that transport oxygen and carbon dioxide. Neither cell type directly participates in immune responses.

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34
Q

Which blood cell type is the most numerous in circulation?

A

Erythrocytes, or red blood cells, constitute the vast majority of cells in circulation, comprising approximately 99% of the total.

35
Q

Among white blood cells, which type is most prevalent?

A

Neutrophils are the most abundant white blood cell type, making up around 60% of the total white blood cell population.

36
Q

What is the typical lifespan of red blood cells compared to other white blood cells?

A

Red blood cells circulate for about four months, while most other white blood cells have lifespans ranging from hours to days.

37
Q

How does the lifespan of lymphocytes differ from other white blood cells?

A

Lymphocytes, particularly those that become memory cells, can have lifespans extending from a few days to as long as 20 years.

38
Q

What are the key characteristics and functions of macrophages?

A

Macrophages are large phagocytic cells that develop from monocytes in tissues. They play a critical role in engulfing and digesting pathogens and cellular debris.

39
Q

How do macrophages move towards sites of infection?

A

Macrophages exhibit chemotaxis, a process of directed movement guided by chemical signals, which allows them to locate and target pathogens.

40
Q

What is the role of dendritic cells in both innate and adaptive immunity?

A

Dendritic cells, named for their long, branch-like projections, efficiently capture pathogens through phagocytosis and then present processed antigens on their surface to activate T cells, linking the innate and adaptive responses.

41
Q

Where are dendritic cells typically found in the body?

A

Dendritic cells are widely distributed and reside in tissues such as the skin and various internal organs.

42
Q

What are the three types of granulocytes, and what distinguishes them?

A

The three types of granulocytes are neutrophils, eosinophils, and basophils, each characterised by the presence of granules in their cytoplasm and distinct staining properties.

43
Q

What is the primary function of neutrophils, and what enzymes do they contain within their granules?

A

Neutrophils are phagocytic cells that play a crucial role in killing ingested bacteria using enzymes like peroxidase and lysozyme stored within their granules.

44
Q

What is a distinctive visual feature of neutrophils under a microscope?

A

Neutrophils are easily identified by their multi-lobed nucleus, which can have three or more lobes.

45
Q

What is the primary role of eosinophils, and what is a distinguishing feature of their morphology?

A

Eosinophils are primarily involved in defending against larger parasites. They have a characteristic bi-lobed nucleus and prominent pink or purple staining granules in their cytoplasm.

46
Q

What are basophils, and what function do they serve in immunity?

A

Basophils are non-phagocytic granulocytes that release active substances from their granules, contributing to inflammation and other immune responses.

47
Q

How do basophils visually differ from eosinophils?

A

Basophils are distinguished from eosinophils by the blue colour of their granules when stained.

48
Q

What is the function of mast cells in the immune system?

A

Mast cells release histamine and other active agents involved in inflammation signaling.

49
Q

What are natural killer (NK) cells, and from which lineage do they originate?

A

NK cells are cytotoxic cells that originate from the lymphoid lineage but are part of the innate immune system.

50
Q

What is the primary target of NK cells, and how do they eliminate these targets?

A

NK cells target infected cells, particularly those harbouring viruses, and malignant cells. They kill by inserting pore-forming molecules into the target cell membrane and releasing cytotoxic chemicals into the target cell’s cytoplasm.

51
Q

How do NK cells differ from cytotoxic T cells in terms of activation?

A

Unlike cytotoxic T cells, NK cells do not require antigen presentation to be activated.

52
Q

What is phagocytosis, and which cells are capable of this process?

A

Phagocytosis is the process by which cells engulf and digest microorganisms and cellular debris. Macrophages, neutrophils, and dendritic cells are capable of phagocytosis.

53
Q

What is the sequence of events involved in phagocytosis?

A

Phagocytosis involves chemotaxis, adherence of the microbe to the phagocyte, ingestion into a phagosome, fusion with a lysosome to form a phagolysosome, digestion, formation of a residual body, and discharge of waste materials.

54
Q

How do phagocytes enhance the digestion of engulfed microbes?

A

Phagocytes generate reactive oxygen species in a process called the oxidative or respiratory burst, which helps to break down and destroy the engulfed microorganisms within the phagolysosome.

55
Q

What is the role of antigen presentation in linking innate and adaptive immunity?

A

Macrophages and dendritic cells, after digesting pathogens, can present fragments of the pathogen’s antigens on their surface. This presentation allows T cells of the adaptive immune system to recognise the threat and initiate a specific response.

56
Q

What are Pathogen-Associated Molecular Patterns (PAMPs)?

A

PAMPs are molecular motifs commonly found across various classes of pathogens but are absent in humans. It’s important to note that while common, they are not present on every single pathogen.

57
Q

What is the nature and typical location of PAMPs?

A

PAMPs are generally glycoconjugates, often attached to lipids embedded in the cell membrane. This surface location makes them accessible for recognition by the host’s immune system.

58
Q

Provide an example of a PAMP, specifying its location.

A

Lipopolysaccharide (LPS) found in the outer membrane of Gram-negative bacteria is a classic example of a PAMP.

59
Q

What are Pattern Recognition Receptors (PRRs), and where are they found?

A

PRRs are receptors located on the surface of innate immune cells like macrophages and dendritic cells.

60
Q

What is the function of PRRs?

A

PRRs bind to PAMPs, triggering an immediate immune response against the pathogen.

61
Q

What is the major family of PRRs?

A

Toll-like receptors represent the primary family of PRRs.

62
Q

What is the role of inflammation in immunity?

A

Inflammation is a major part of innate immunity, serving as the body’s immediate response to infection or injury.

63
Q

What triggers the inflammatory response in innate immunity?

A

When macrophages recognise pathogens, they release signalling molecules like cytokines and chemokines that trigger the inflammatory response.

64
Q

Describe the key vascular changes that occur during inflammation.

A

Blood vessels in the affected area become more permeable, causing the area to swell as fluids leak into the tissues. Leukocytes also adhere more to the endothelial cells of the blood vessels and pass between them to enter the tissues.

65
Q

How does inflammation affect leukocyte behaviour?

A

Inflammation causes leukocytes to adhere to the endothelial cells lining blood vessels and then migrate into the surrounding tissues.

66
Q

What is the typical order of leukocyte arrival at a site of inflammation?

A

Neutrophils are often the first leukocytes to arrive at the site of inflammation, followed by monocytes which then differentiate into macrophages.

67
Q

What is the relevance of inflammation to adaptive immunity?

A

Inflammation is also important for adaptive immunity because lymphocytes, specifically T cells and B cells, are drawn to the site of inflammation.

68
Q

What are cytokines, and what role do they play in the immune system?

A

Cytokines are small protein signalling molecules used by both the innate and adaptive immune systems. They function as communication signals between various immune cells.

69
Q

How do the signalling mechanisms of cytokines compare to hormones?

A

Cytokines can act in autocrine, paracrine, or even endocrine manners, making their distinction from hormones sometimes blurry.

70
Q

List three examples of cytokine families and their functions.

A

Examples include interleukins (signalling between leukocytes), chemokines (inducing chemotaxis), and interferons (released by virus-infected cells to warn nearby cells).

71
Q

What are acute phase proteins (APPs), and how are they classified?

A

APPs are humoral factors whose concentration in the blood either increases (positive APPs) or decreases (negative APPs) in response to inflammation.

72
Q

Provide two examples of positive APPs and describe their role in immunity.

A

C-reactive protein and complement factors are positive APPs that can function as opsonins, molecules that tag microbes for phagocytosis.

73
Q

What is opsonisation, and how does it contribute to the immune response?

A

Opsonisation is the process of labelling microbes for phagocytosis. It enhances the efficiency of phagocytic cells in engulfing and destroying pathogens.

74
Q

What is the complement system, and how is it related to the immune system?

A

Complement is part of the innate immune system but links to the adaptive immune system through its interactions with antibodies.

75
Q

Describe the composition of the complement system.

A

The complement system consists of over 20 different globular proteins, primarily produced by the liver, that circulate in the blood plasma.

76
Q

Explain the mechanism of action of the complement system.

A

Complement proteins work in a cascade, where one protein cleaves the next protein in the sequence, activating it and triggering a chain reaction.

77
Q

What is the key event where the different complement activation pathways converge?

A

The three complement activation pathways converge at the cleavage of inactive C3 protein into active C3a and C3b fragments.

78
Q

What is the ultimate outcome of the complement cascade?

A

The complement cascade culminates in the formation of a membrane attack complex (MAC) that punches holes in the cell membranes of pathogens, leading to their destruction.

79
Q

Name the three initial pathways of complement activation.

A

The three pathways are the classical pathway, the alternative pathway, and the lectin pathway.

80
Q

Describe the classical pathway of complement activation.

A

The classical pathway involves antibodies (immunoglobulin M or G) binding to antigens on a pathogen’s surface, activating the C1 protein complex, and initiating a protein cleavage cascade.

81
Q

Explain the alternative pathway of complement activation.

A

The alternative pathway involves the direct interaction of C3 protein with the pathogen surface, leading to C3 cleavage without the need for antibodies.

82
Q

How does the lectin pathway activate the complement cascade?

A

The lectin pathway is triggered when mannose-binding lectin, a protein, binds to mannose, a sugar present on the surface of pathogens. This binding initiates a protein cleavage cascade.

83
Q

Apart from the formation of MAC, what are the other outcomes of complement activation?

A

Complement activation also produces fragments like C3a and C5a that contribute to inflammation and C3b that acts as an opsonin to enhance phagocytosis.

CTB Block 2 (19 decks)

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