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PATH30001 - Mechanisms of Disease > Lecture 11 - Immunodeficiencies > Flashcards

Lecture 11 - Immunodeficiencies Flashcards

1
Q

What is innate immunity made up of?

A

First line:
• Physical barriers
• pH
• Secretions

Second line:
• Innate immune cells

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2
Q

Describe the role of DC’s

A
  • ‘Sentinels’
  • Link between innate and adaptive immunity
  • PAMP recognition with PRRs
  • T-lymphocyte co-stimulation
  • Nature of their function dependent on cytokine signalling
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3
Q

What are the critical features of adaptive immunity?

A
  • Slower to be induced
  • Memory function
  • Recognises specific antigen
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4
Q

What are the different type of B cells?

A
  • B-1
  • B-2
  • Marginal zone B cells (MZB)
  • Follicular B cells
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5
Q

Describe the kinetics of immune protection after vaccination

A

→ Vaccination

  1. Induction of the primary immune response; IgM
  2. Response dies back, pool of memory cells present

→ Exposure to antigen from environment
3. Induction of immune response more quickly and to a greater magnitude; IgG, IgA

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6
Q

What are the main difference between the primary and secondary immune responses?

A

Secondary:
• greater magnitude
• more quickly induced
• class switched Ig (e.g. IgG, IgA)

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7
Q

Can IgA or IgM be monomers?

A

IgM: no
IgA: yes

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8
Q

What is the structure and function of memory B cells?

A
  • Surface bound immunoglobulins

* hang around after the immune response has been resolved, waiting for the next exposure to the antigen

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9
Q

Compare T-dep. and T-independent antigen, and the respective immune responses

A

T-dependent:
• usually protein
• T cell help available to B cells
→ longer lived, more robust response

T-independent: 
 • polysaccharide
 • no T cell help available to B cells 
→ short lived response
 • no SHM or CSR
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10
Q

Describe the role and function of Treg

A 
Suppressive effects on:
 •  granulocytes
 • DC's
 • B cells
 • Th2
 • Th1
 • Th17
 • T cell migration to tissues
Under normal conditions, control allergy, autoimmunity and inflammation
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11
Q

What are the markers of Treg?

Why is this important?

A
  • CD25
  • CD4

• FoxP3 (transcription factor)

Deficiency in FoxP3 leads to deficiency of Treg.
This is called IPEX syndrome

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12
Q

What are the generalised outcomes of immune system defects?

A
  • Autoimmunity
  • Allergy
  • Immunodeficiency
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13
Q

Define Immunodeficiency

A

A group of disorders where part of the immune system is missing or defective

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14
Q

What are the two categories of immunodeficiency?

Give examples for each

A

Primary: inherited (HIGM)
Secondary: acquired (HIV/AIDS)

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15
Q

What is PID?
Describe some features.
When is the onset?
What are the various classes?

A

Primary immune deficiency
• 150 different conditions
• most are rare
• inherited

Onset is usually in childhood, but can in adulthood

Classes in order of prevalence:
 • Antibody
 • Combined
 • Phagocytic
 • Cellular
 • Complement
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16
Q

What are clinical signs of PID used for diagnosis?

A

Combination of patient history w/ lab tests

Patient history:
 • >10 cases of otitis media per year
 • >2 cases of pneumonia
 • >2 life threatening infections per lifetime
 • >2 sinus infections per year

Lab tests:
• Low Ig levels (in general, or of specific classes)
• Cellular deficiencies

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17
Q

What are the pathological features of PID?

A

• Recurrent deep skin or organ abscesses

• >2 deep-seated infections such as meningitis,
osteomyelitis, cellulitis or sepsis

  • oral thrush or Candida infection
  • Autoimmune phenomena
  • Dysmorphic features associated with recurrent infection
  • Infections that worsen chronic disorders (eg. asthma)
  • Infections with pathogen despite vaccine (eg pneumococcal)
18
Q

Give some specific examples of PID

A
  1. T cell
    • IPEX
    • SCID
  2. B cells
    • CVID
    • SAD
  3. Innate deficiency
    • Chronic granulomatous disease
    • IRAK-4
19
Q

What are some Antibody deficiencies?

A
  • CVID
  • SAD

(HIGM, agammaglobulinaemia; but these aren’t death with in this lecture)

20
Q

What are some T-cell deficiencies?

A
  • SCID (severe combined immune deficiency)

* IPEX syndrome

21
Q

Describe the general features CVID

What is the cause?

A

Normal numbers of B cells, but they do not develop properly in plasma cells to produce Ab

  • One of the most common PID’s
  • V. low levels of serum Ig
  • Increased susceptibility to infection due to this Ab deficiency

• Affects multiple organs (lungs, GIT, spleen, ears, blood)

Causes:
Mutations in:
• TACI
• ICOS
• CD19
22
Q

What are the pathological outcomes of CVID seen around the body?

A 
1. Frequent lung infections
• Sinusitis
• Pneumonia
• Bronchitis
• Otisis
  1. Enlarged lymph nodes & spleen
  2. Polyarthritis
23
Q

What are the treatment options for CVID?

What about SAD?

A
  • Intragam (IVIg)
  • Antibiotics for the infections

Same for SAD

24
Q

What is the main features of SAD?
What is lacking?
What isn’t?

A

(Specific antibody deficiency)
• Failure to produce normal Ab levels against specific polysaccharide antigens
(IgG2?)

NB
• Normal general Ig levels, and normal Ig subclasses, and normal response to protein antigens
• It is only Ig against very specific antigens that are absent

25
Q

What is the main complication of SAD?

Why?

A

Pneumococcal infection

Antigen that is normally recognised by the immune system is polysaccharide

In SAD, there is failure to produce antibody against polysaccharide antigens

26
Q

Which people are most commonly affected by Pneumococcal disease and why?

A

Who:
Children, elderly, SAD patients

Reason:
• The antigen is T-cell independent
• Children are yet to develop the required response
• Immunocompromised individuals lack the response
• Elderly has lost the required response

27
Q

What is an important structural feature of S. pneumoniae?

A

Polysaccharide capsule

28
Q

Describe how SAD is diagnosed in the lab

A
  1. Response to pneumococcal polysaccharide antigens
    • Patient exposed to 23 different p.p. antigens
    • If the patient responds to less than half, we diagnose with SAD
    (NB respond indicates IgG specific for the antigen produced)
  2. No memory B cells
    • Using flow cytometry
29
Q

What’s wrong with ‘Bubble boy’?

A

SCID: severe combined immune deficiency

30
Q

Describe the features of SCID, as well as the cause(s)

A

Immune system lacks:
• T cells
• B cells
• NK cells

• Severe susceptibility to infection

Cause:
• Many genetic causes identified to date
e.g.; 
• cγ mutation
• IL-7α
• JAK3
31
Q

What is IPEX syndrome?

Describe some features including pathogenesis

A

(Immunodysregulation polyendocrinopathy enteropathy X- linked syndrome)

• Very rare

Pathogenesis:
• Mutation in FoxP3 (marker of Tregs)
• Lack of functional Treg
→ multiple autoimmune disorders and allergies

32
Q

Describe the pathology of IPEX

A
  • Absence of small bowel mucosa
  • Inflammatory infiltrate in many organs
  • Steatosis in liver
  • Nephritis
  • Eczematous skin
  • No goblet cells
  • Atrophy of villi in duodenum
33
Q

What is Chronic granulomatous disease?

What is the cause?

A
  • Innate immune deficiency
  • Neutrophils / macrophages cannot produce superoxide
  • Cannot kill phagocytosed bacteria

Cause:
• Mutations in NAPDH oxidase

34
Q

What are some examples of innate immune deficiency?

A
  • IRAK-4 deficiency

* Chronic granulomatous disease

35
Q

What is IRAK-4?

A

Interleukin-1 receptor associated kinase-4

It is a protein kinase involved in the intracellular transduction pathway after TLRs and Interleukin signalling

36
Q

Describe the pathogenesis of IRAK-4 deficiency

Which infections will one be susceptible to?

A
  • Lack of IRAK-4
  • Impaired IL-1 and TLR signalling
  • Impaired T-cell activation

Infection:
• Susceptible to pyogenic bacteria
• Not susceptible to viruses or fungi

37
Q

Which disorders can probiotics help?

A

Some success seen in allergies

38
Q

Which ‘helper’ T cell is usually induced in an immune response?

A

Th1

39
Q

What is the function of Th2?

A

Helminth immunity

Allergy

40
Q

What is the function of Th17?

A

Immunity against extracellular bacteria

41
Q

Which classes of Ig can be transported across the mucosa?

A

Only IgA1 and IgA2

42
Q

What is CVID also known as?

A

Hypogammaglobulinaemia

PATH30001 - Mechanisms of Disease (34 decks)

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