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2. CP - Core Immunology > (11) Immunodeficiency > Flashcards

(11) Immunodeficiency Flashcards

1
Q

What are the 2 main categories of the immune system?

A
  • innate

- adaptive

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2
Q

What are the 2 main components of the adaptive immune system?

A
  • humoral

- cellular

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3
Q

Give 5 major components of the innate immune system

A
  • pattern recognition receptors (PRR)
  • antimicrobial peptides
  • cells
  • complement components
  • cytokines
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4
Q

Pattern recognition receptors (PRR) are a major component of the innate immune system. Give examples

A
  • toll-like receptors (TLRs)
  • NOD-like receptors (NLRs)
  • Rigl-like receptors (RLRs)
  • C-type lectins (CLRs)
  • Scavenger receptors
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5
Q

What are pattern recognition receptors? (PPRs)

A

Proteins expressed by cells of the innate immune system to identify two classes of molecules: pathogen-associated molecular patterns (PAMPs), which are associated with microbial pathogens, and damage-associated molecular patterns (DAMPs), which are associated with cell components that are released during cell damage or death

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6
Q

Antimicrobial peptides are a major component of the innate immune system. Give examples

A
  • defensins
  • cathelin
  • protegrin
  • granulsyin
  • histatin
  • secretory leukoprotease inhibitor
  • probiotics
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7
Q

Cells are a major component of the innate immune system. Give examples

A
  • macrophages
  • dendritic cells
  • NK cells
  • NK T-cells
  • neutrophils
  • eosinophils
  • mast cells
  • basophils
  • epithelial cells
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8
Q

Complement components are a major component of the innate immune system. Give examples

A

Classic and alternative complement pathway, and proteins that bind complement component

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9
Q

Cytokines are a major component of the innate immune system. Give examples

A
  • autocrine cytokines
  • paracrine cytokines
  • endocrine cytokines

These mediate host defense and inflammation, as well as recruit, direct and regulate adaptive immune responses

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10
Q

What is the function of B lymphocytes?

A

Develop potential to secrete antibodies: humoral immunity

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11
Q

Give 3 types of T lymphocytes

A
  • killer/cytotoxic T lymphocytes
  • helper T lymphocytes
  • suppressor T lymphocytes
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12
Q

What is the function of killer/cytotoxic T cells?

A

Able to kill. Cellular immunity

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13
Q

What is the function of helper T cells?

A

Secrete growth factors (cytokines) which control immune response. Help B cells and T cells

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14
Q

What is the function of suppressor T cells?

A

May dampen down the immune response

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15
Q

Which type of T cell is a target of HIV?

A

Helper T cells

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16
Q

In what ways does the binding of antibodies to antigens inactivate antigens?

A
  • neutralisation
  • agglutination of microbes
  • precipitation of dissolved antigens
  • activation of complement system
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17
Q

Neutralisation is a way in which antigens are inactivated through the binding of antibodies. What does neutralisation mean?

A
  • virus = blocks viral binding

- bacteria = coats bacteria

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18
Q

Neutralisation, agglutination of microbes and precipitation of dissolved antigens are ways in which antigens are inactivated by the binding of antibodies. Why are these 3 methods effective?

A

They enhance phagocytosis by macrophages

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19
Q

Activation of the complement system is a way in which antigens are inactivated by the binding of antibodies. What does this lead to?

A

Cell lysis

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20
Q

Describe the process of a cytotoxic T cell destroying an infected cell

A
  1. cytotoxic T cell binds to infected cell (the infected cell presents self-nonself complex and foreign antigens which allows cytotoxic T cell to bind)
  2. perforin (in cytotoxic T cell) makes holes in infected cell’s membrane and enzyme enters (the enzyme promotes apoptosis)
  3. the infected cell is destroyed
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21
Q

What is immunodeficiency?

A
  • Clinical situations where the immune system is not effective enough to protect the body against infection
  • Can occur at any age
  • Children and elderly are much more sensitive to infection
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22
Q

Immunodeficiency is usually secondary to what?

A

Usually secondary to the effects of external factors

  • stress
  • surgery/burns
  • malnutrition
  • cancer
  • immunosuppressive effects of drugs inc. cancer therapy
  • irradiation (clinical or other)
  • AIDS
  • Other infections eg. Measles, TB
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23
Q

Secondary/acquired immunodeficienies can be caused by cancer. Especially which type?

A

Lymphoprofilerative disease

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24
Q

Some immunodeficiencies are primary immunodeficiencies caused by what?

A

Genetic defects in individual components of the immune system

25
Q

How common are primary immunodeficiencies?

A

Very rare

Often diagnosed in early childhood but can present in adult life

Recurrent infection often suggests immunological problem

26
Q

What is the role of IRAK?

A
  • toll-like receptors at surface of cells of innate immune system
  • these will recognise bacterial molecules e.g. flagellin etc
  • this sets off intracellular signalling which feeds into IRAK
  • this causes IRAK to lead to the production of NF-kB
  • NF-kB is an essential transcription factor needed to produce pro-inflammaotry cytokines IL-1, TNF and IL-6 and therefore needed for an immune response
27
Q

Give an example of a possible case where the patient has IRAK deficiency

A
  • boy 12 months
  • history of recurrent pneumococcal pneumonia
  • vaccination up to date
  • no family history
  • normal levels of immunoglobulins
  • normal numbers of lymphocytes and neutrophils
  • CRP only marginally elevated during infection
28
Q

If a patient has recurrent infections but no family history of the same problem, what does this indicate?

A

Not a primary immunodeficiency as these are often inherited due to germ line mutations

29
Q

What does normal levels of immunoglobulins suggest?

A

Normal B cell function

30
Q

When IRAK causes the production of NF-kb, what happens?

A

It is a transcription factor which leads to the production of pro-inflamamotry cytokines (IL-1, TNF, IL-6)

Temperature will go up, massive neutrophil response - essential to tell rest of immune system

31
Q

What is the nitroblue tetrazolium test (NBT) for and what are you looking to see?

A

Test to see whether the neutrophils are working properly

Incubate neutrophils with the dye, neutrophils that are working properly will convert the pale blue colour into a dark blue colour

32
Q

How does the nitroblue test work? (what is the basis behind it)

A
  • neutrophil phagocytoses bacteria
  • H+ ion enters into the phagosome
  • pH inside phagosome becomes acidic in order to activate proteolytic enzymes and kill the bacteria
  • hydrogen peroxide is produced which converts the light blue dye to dark blue

Neutrophils that are not working cannot transport the H+ and therefore are unable to kill the bacteria that is inside the phagosome - they therefore also do not change the colour of the dye

33
Q

Give an example of how a patient with chronic granulomatous disease (CGD) might present?

A
  • boy 6 years old
  • history of recurrent skin abscesses
  • presented to hospital with a liver abscess
  • no fx of similar problems
  • normal immunoglobulins, lymphocytes and neutrophil count
34
Q

What are the complications associated with chronic granulomatous disease (CGD)?

A
  • osteomyelitis
  • pneumonia
  • swollen lymph nodes
  • ginigivitis
  • non-malignant granulomas
  • inflammatory bowel disease
35
Q

What is chronic granulomatous disease?

A

Hereditary disease (mostly gp91 X-linked) where the neutrophils cannot form the reactive oxygen compounds used to kill ingested pathogens - leads to the formation of granulomata in many organs

36
Q

Give example on how a patient might present with absent terminal complement pathway activity?

A
  • female 8 years old
  • 2 previous episodes of meningococcal meningitis
  • no family history
  • normal immunoglobin profile
  • normal numbers of lymphocytes
  • normal numbers and function of neutrophils
  • absent terminal complement pathway activity!
37
Q

How would you test for terminal complement pathway activity?

A
  • incubate sheep RBC with patient serum
  • cannot use own human RBC as our RBC have components that will inhibit our complement system against our own RBC
  • complement in serum should become activated and destroy sheep RBC (lysis)

Sheep RBC + antibody to sheep RBC = haemolysis

38
Q

What are the 3 different pathways in the complement system?

A
  • classical pathway
  • MB-lectin pathway
  • alternative pathway
39
Q

What happens at the beginning of the activation of the classical complement pathway?

A

Immune complex activates complement by triggering C1 component

40
Q

What do all 3 complement pathways lead to?

A

Conversion of C3 convertase

C3 convertase is an enzyme that cleaves C5

C5 will allow the rest of the complement (C6-C9) to settle on the surface of the bacteria

Creates pores - leads to osmolytic cell lysis/cell killing

41
Q

Absent terminal complement pathway leads to a deficiency of which component?

A

C8 deficiency

Therefore cannot create the whole pore

Therefore osmolytic cell lysis cannot occur

42
Q

Absent terminal complement pathway makes you particularly susceptible to which infection?

A

Meningococcal infections

43
Q

What is the current management/treatment of meningococcal infections?

A

There are now effective vaccines for all strains

Also have penicillin prophylaxis

44
Q

What is X-linked agammaglobulinaemia?

A

Antibody deficiency

45
Q

How might a patient with agammaglobulinaemia present?

A
  • boy 3 years
  • history of recurrent wino-pulmonary infections
  • 1 hospitalisation for pneumonia
  • vaccination status up to date
  • maternal uncle has history of recurrent chest infections and bronchiectasis
  • CXR and CT show some evidence of bronchial dilatation
  • immunoglobulin profile: very low or undetectable IgG, IgA, IgM
  • lymphocyte markers: absent peripheral B cells and normal T cells
46
Q

What do defects in B cells lead to?

A
  • different degrees of loss of antibody secretion

- usually leads to recurrent bacterial infection with pyogenic organisms

47
Q

Which types of infections are lack of antibodies/defects in B cells associated with?

A

Sino-pulmonary infections

pyogenic organisms

48
Q

When are defects in B cells normally diagnosed?

A

Around 1-2 years since the maternal IgG antibodies provide protection for the first few months

49
Q

How are defects in B cells treated?

A

Treat infection with antibiotics then give IgG for life (blood transfusion)

50
Q

How serious are B cell defects?

A

Most are very serious

Some are less serious eg. IgA deficiency (1 in 5-700 not severely immunodeficient)

51
Q

Give some examples of primary B-cell deficiencies

A
  • common variable immunodeficiency
  • X-linked agammaglobulinaemia
  • autosomal recessive hyper IgM syndrome
  • IgA deficiency
  • IgG subclass deficiency
  • transient hypogammaglobulinaemia of infancy
52
Q

How might a patient with a primary immunodeficiency present?

A
  • female 3 months
  • severe herpes zoster infection
  • hospitalised with extensive oro-pharyngeal candida
  • parents first cousins
  • sibling died at age of 4 months with sepsis
  • normal levels of IgG, no IgA and reduced IgM
  • lymphocyte markers: absent/reduced T and NK cells but present B cells
53
Q

Why might a baby with primary immunodeficiency have normal levels of IgG?

A

Maternal origin

Whereas IgA is not maternally transferable

54
Q

If you see absent or reduced T cells, what is this a warning for?

A

Severe combined immunodeficiency (SCID)

55
Q

Are defects in T cells more or less severe than defects in B cells?

A

Usually more dramatic since B cells also need T cell help

56
Q

What are the symptoms of T cell defects?

A

Recurrent infection with opportunistic infections, bacteria, viruses

Fungi (candida), protozoa (pneumocystis)

57
Q

What is a defect in both B and T cells?

A

Severe combined immunodeficiency syndromes (SCID)

58
Q

What is used to treat SCID?

A
  • bone marrow transplantation

- gene therapy

59
Q

Give some examples of primary T cell deficiencies

A
  • severe combined immunodeficiency syndromes
  • adenosine deaminase deficiency
  • purine nuceloside phosphorylase deficiency
  • MHC class II deficiency
  • Wiskott-Aldrich syndrome

2. CP - Core Immunology (7 decks)

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