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Immunodeficiencies Flashcards

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1
Q

How is immunodeficiency classified?

A

Primary (congenital)
- defect in immune system

Secondary (acquired)
- caused by another disease

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2
Q

What are the clinical features of immunodeficiencies

A

Recurrent infections

  • <6-8 URI/year for 1st 10 yrs
  • 6 otitis media
  • 2 gastroenteritis/year for 1st 2-3 years

Severe infections, unusual pathogens (Aspergillus, Pneumocystis), unusual sites (liver abscess, osteomyelitis)

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3
Q

Outline the warning signs of Primary immunodeficiency

A
  • 8+ new ear infections within 1 year
  • 2+ serious sinus infections within 1 year
  • 2+ months on antibiotics w/ little effect
  • 2+ pneumonias in 1 year
  • Infant fails to gain weight / grow normally
  • Recurrent, deep skin or organ abscesses
  • Persistent thrush (mouth/elsewhere on skin) after age 1
  • Need for IV antibiotics to clear infections
  • 2+ deep-seated infections
  • Family history of primary immunodeficiency
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4
Q

What is the main cause of PID?

A

Usually genetic

- Infrequent but can be life-threatening

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5
Q

What are the major consequences of Primary immunodeficiency (PID)?

A

Adaptive immune system defects: T and B cell

Innate immune system lacks; phagocytes, complement

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6
Q

Describe the frequency of primary immunodeficiency of immune cells

A

50% antibody
30% T Cell

18% phagocytes
2% complement

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7
Q

How are defects in adaptive immunity classified?

A

Sub-classification: primary component affected e.g.

  • B cells
  • T cells
  • Combined (both B & T)
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8
Q

What cellular defects occuring adaptive immunity during primary immunodeficiency?

A

T cell defects impair antibody production

Defects in lymphocyte development or activation

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9
Q

Name the major B-lymphocyte immunodeficiency disorders

A
  • X-linked agammaglobulinemia (Bruton’s disease)
  • Common variable immunodeficiency (CVID)
  • Selective IgA deficiency
  • IgG2 subclass deficiency
  • Specific Ig deficiency with normal Igs
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10
Q

What is the first described immunodeficiency?

A

X-linked Agammaglobulinemia

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11
Q

What causes Bruton’s disease?

A

Defect in btk gene (X chromosome)

form of agammaglobulinemia

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12
Q

What is the role of the btk gene?

A

Encodes Bruton’s tyrosine kinase

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13
Q

What is the effect of btk gene defect?

A

Btk needed for pre-B cell receptor signalling

Blocks in B-cell development (stop at pre-B cells)

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14
Q

What is the consequence of Bruton’s disease?

A

Recurrent severe bacterial infections

  • 2nd half of first year (lung, ears, GI)
  • autoimmune diseases (35% of patients)
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15
Q

How do we investigate Brutons disease?

A
  • B cells absent / low;
  • Plasma cells absent
  • All Igs absent / very low
  • T cells + T cell-mediated responses normal
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16
Q

How is brutons disease treated?

A
  • IVIg: 200-600mg/kg/month at 2-3 wk intervals
  • or subcutaneous Ig weekly
  • prompt antibiotic therapy (URI /LRI)
  • Do not give live vaccines
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17
Q

What is SCID?

A

Severe Combined ImmunoDeficiency (SCID)

A form of Combined immunodeficiencies

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18
Q

Outline the predominant T cell disorders

A
  • DiGeorge syndrome
  • Wiskott-Aldrich syndrome
  • Ataxia-telangiectasia
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19
Q

Which lymphocyte disorder is SCID a form of?

A
  • involves both T and B

- 50-60% X-linked; rest - autosomal recessive

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20
Q

Describe the presentation of SCID

A
  • well at birth; problems > 1st month
  • diarrhoea; weight loss; persistent candidiasis
  • severe bacterial/viral infections
  • failure to clear vaccines
  • unusual infections (Pneumocystis, CMV)
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21
Q

What are the different causes of SCID?

A

Different causes; affect T & B cell development e.g.

  • Cytokine receptor defects
  • RAG defects
  • Adenosine Deaminase Deficiency
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22
Q

How do cytokine receptor defects effect T and B cell development?

A

Common cytokine receptor γ-chain defect
(signal transducing component of receptors for IL-2, 4, 7, 9, 11, 15, 21)

IL-7 needed for survival T cell precursors => defective T cell development => lack in B cell help (low Ab)

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23
Q

What is the effect of RAG enzyme defects?

A

RAG-1/RAG-2 defect => no T and B cells

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24
Q

What is the effect of adenosine deaminase deficiency?

A

Accumulation of deoxyadenosine & deoxy-ATP => toxic for rapidly dividing thymocytes

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25
How is SCID investigated?
Lymphocyte subsets - T, B, NK (% and numbers) => low total lymphocyte count Pattern: - T very low/absent - B normal/absent sometimes NK also absent (γ-chain defect affecting IL-15 receptor) - Igs low - T cell function ↓ (proliferation, cytokines)
26
How is SCID treated?
- Isolation - Do not give live vaccines ! - Blood products from CMV -ve donors - IVIg replacement - Treat infections - Bone marrow/ HSCT - Gene therapy (for ADA and γ-chain genes)
27
Describe SCID prognosis and survival
Dependent on promptness of diagnosis Survival >80% - early diagnosis - good donor match no infections pre-transplant Survival <40% - late diagnosis - chronic infections - poorly matched donors Regular monitoring post BMT => engraftment
28
What is DiGeorge syndrome?
Complex array of developmental defects
29
What are the physical signs of DiGeorge syndrome?
Dysmorphic face: cleft palate, low-set ears, fish-shaped mouth
30
What are the clinical symptoms of DiGeorge syndrome?
Hypocalcaemia, cardiac abnormalities Variable immunodeficiency (absent/reduced thymus => affects T cell development)
31
What is Wiskott-Aldrich SYndrome (WAS)?
X-linked Defect in WASP (protein involved in actin polymerisation => defect in signalling)
32
What are the clinical signs of Wiskott-aldrich syndrome?
Thrombocytopaenia, eczema, infections
33
Describe the progression of wiskott aldrich syndrome?
Progressive immunodeficiency (T cell loss) Progressive ↓ T cells; ↓ T cell proliferation Ab production (↓ IgM, IgG; high IgE, IgA)
34
What is ataxia telangiectasia?
Autosomal recessive Defect in cell cycle checkpoint gene (ATM) => sensor of DNA damage => activates p53 => apoptosis of cells with damaged DNA
35
What is the role of the ATM gene?
ATM gene stabilises DNA double strand break complexes during V(D)J recombination => defect in generation of lymphocyte antigen receptors & lymphocyte development
36
What are the consequences of ataxia telangiectasia?
Progressive cerebellar ataxia (abnormal gait) Typical telangiectasia (ear lobes, conjunctivae) Immunodeficiency Increased incidence of tumours later in life
37
What are the causes of ataxia telangiectasia?
- Combined immunodeficiency (B & T) - Defects in production of switched Abs (IgA/G2) - T cell defects (less pronounced) => thymic hypoplasia - Upper & lower respiratory tract infections - Autoimmune phenomena, cancer
38
What are the 2 types of innate immunity defects?
- Phagocyte defects | - Complement defects
39
What are the types of phagocyte defects?
Quantitative (↓ number) Qualitative - Chronic granulomatous disease - Chediak-Higashi syndrome - Leukocyte adhesion defects (LADs)
40
What is chronic granulomatous disease?
Defective oxidative killing of phagocytosed microbes; mutation in phagocyte oxidase (NADPH) components - Formation of granulomas (wall off microbes)
41
How is chronic granulomatous disease?
Diagnosis: Tests that measure oxidative burst: - NBT test (nitroblue tetrazolium reduction) - Flow cytometry assay dihydrorhodamine
42
Outline how an NBT reduction test is carried out?
1. Control neutrophils + Patient neutrophils 2. Incubate in nitroblue tetrazolium 3. Activate using microbe / cytokines 4. Checks production of active oxygen species 5. If oxygen species produced; cells cleave active dye = blue 6. Deficient patients have no colour as they are defective
43
How is a dihydrorhodamine assay used to diagnose chronic granulomatous disease?
Dihydrorhodamine assay used in similar manner Cells producing active oxygen species will cleave the dye making the cells fluoresce, if deficient no fluorescence will occur Takes ~30 mins
44
What is Chediak-Higashi Syndrome?
- rare genetic disease - defect in LYST gene - neutrophils have defective phagocytosis - repetitive, severe infections
45
What is the role of the LYST gene?
Regulates lysosome traffic
46
What causes recurrent infections in chediak-higashi syndrome?
Defect phagosome-lysosome fusion => defective killing of phagocytosed microbes => recurrent infections
47
How is Cjhediak-Higashi Syndrome diagnosed?
- Necreased number neutrophils | - Neutrophils have giant granules
48
What defects cause LAD (Leukocyte Adhesion Deficiency)?
- Defect in β2-chain integrins (LFA-1, Mac-1) | - Defect in sialyl-Lewis X (selectin ligand)
49
Describe the presentation of leukocyte adhesion deficiency
Skin infections, intestinal + perianal ulcers
50
How is leukocyte adhesion deficiency investigated?
↓ neutrophil chemotaxis | ↓ integrins on phagocytes (flow cytometry)
51
What is the effect of complement deficiencies?
Can affect different complement factors severe/fatal pyogenic infections (C3 deficiency) Predisposition to infection with different pathogens
52
What are the symptoms of complement deficiencies?
Symptoms differ depending on C factor affected
53
What recurrent infections occur in complement deficiencies?
Recurrent infections (Neisseria) - deficiency terminal complex (MAC): C5, C6, C7, C8 & C9 Severe/fatal pyogenic infections (C3 deficiency) SLE-like syndrome (C1q, C2, C4 deficiency)
54
What is Hereditary angioneurotic oedema?
Failure to inactivate complement (deficiency in C1 inhibitor); intermittent acute oedema skin/mucosa => vomiting, diarrhoea, airway obstruction
55
How are complement deficiencies investigated?
- measure individual components | - complement function: CH50 (haemolysis)
56
What are the aims of primary immunodeficiency treatments?
- Ig replacement therapy - Bone marrow transplantation - Gene therapy - Prompt infection treatment - Prevention of infection: isolation, antibiotic prophylaxis, vaccination (not live vaccines!) - Good nutrition
57
What are the secondary immunodeficiency causes?
``` Infections: viral, bacterial Malignancy Extremes of age Nutrition (anorexia, iron deficiencies) Chronic renal disease Splenectomy Trauma/surgery, burns, smoking, alcohol Immunosuppressive drugs ```
58
Outline common secondary immunodeficiency infections
Viral: - HIV, CMV, EBV, - Measles - Influenza Chronic bacterial: - TB - Leprosy Chronic parasitic: - Malaria - Leishmaniasis Acute bacterial - Septicaemia
59
What malignancies cause immunodeficiency?
- Myeloma - Lymphoma (Hodgkin’s, non-Hodgkin’s) - Leukaemia (acute or chronic)
60
What are the age extremities causing immunodeficiency?
prematurity | old age
61
How does prematurity cause immune vulnerability?
- infants < 6 months => maternal IgG | - premature delivery: interrupts placental transfer of IgG => infant Ig deficient
62
How does old age affect the immune system?
Decline in normal immune function

Immunology (14 decks)

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