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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
  • Severe infections, unusual pathogens (Aspergillus, Pneumocystis), unusual sites (liver abscess, osteomyelitis). - An immunocompetent patient is not infected by these pathogens
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3
Q

Outline the warning signs of Primary immunodeficiency

A
  • Recurrent infections, esp. frequent thrush/fungal infections(= unusual)
  • Require ↑ antibiotics
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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 does Primary immunodeficiency (PID) usually cause?

A

Innate immune system lacks; Phagocytes, Complement

Adaptive immune system defects: T-cells, B cells.

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6
Q

How are defects in adaptive immunity classified?

A

Sub-classification: primary component affected e.g.

  • B cells
  • T cells
  • Combined (both B & T) = SCID
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7
Q

What cellular defects occur in adaptive immunity during primary immunodeficiency?

A

T cell defects impair antibody production

Defects in lymphocyte development or activation

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8
Q

Counterintuitively, a patient with an immunodeficiency could simultaneously present with ……..

A

Autoimmunity

Immunodeficient = lacking an element of immunity
+
Autoimmunity = Damage body’s own tissues bc the immune defect also affects elements of the immune system that regulate other immune cells

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9
Q

Defects in earlier stem cells affect ……

Defects at a later stage lead to a more …………. pathology

A

-the entire immune system - e.g. defects in HSCs/common lymphoid progenitor/common myeloid progenitor
= affects many immune cells

-restricted - e.g. mature T-cells/mature B-cells/plasma cells - e.g. 1 particular T-cell/B-cell

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10
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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11
Q

What is the first described immunodeficiency?

A

X-linked Agammaglobulinemia

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12
Q

What causes Bruton’s disease (agammaglobulinemia) ?

A

Defect in BTK gene (X chromosome)

BTK gene encodes Bruton’s tyrosine kinase

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13
Q

What is the role of the btk gene?

A

Encodes Bruton’s tyrosine kinase

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14
Q

What is the effect of BTK gene defect?

A

BTK needed for pre-B cell receptor signalling

BTK defect blocks B-cell development (stop at pre-B cells)

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15
Q

What is the consequence of Bruton’s disease?

A
  • Recurrent severe bacterial infections

- Autoimmune diseases

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16
Q

What inheritance pattern does agammaglobulinaemia follow?

A

Agammaglobulinaemia = X-linked

Carrier mother + unaffected father = affected male offspring

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17
Q

What happens to B-cell at Pro-B stage?

A

Pro-B cell rearranges its Ig(BCR)

At Pre-B stage, B-cell now presents a pre-BCR on its surface

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18
Q

Pre-B cell requires …… downstream in order to continue development

A

BTK signal

Missing in agammaglobulinaemia = no subsequent B-cell development = patients lack B-cell + Ab production

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19
Q

How do we diagnose Brutons disease (agammaglobulinaemia)?

A
  • B cells absent / low; Plasma cells absent
  • All Igs absent / v. low
  • T cells + T cell-mediated responses normal

agammaglobulinaemia = B-cell restricted immunodeficiency

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20
Q

How is brutons disease (agammaglobulinaemia) treated?

A
  • IV Ig/Subcutaneous Ig
  • Prompt antibiotic therapy (URI /LRI)
  • Do not give live vaccines bc cannot clear the pathogen
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21
Q

What is SCID?

A

Severe Combined ImmunoDeficiency (SCID)

A form of Combined immunodeficiencies

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22
Q

Outline the predominant T cell disorders

A
  • DiGeorge syndrome
  • Wiskott-Aldrich syndrome
  • Ataxia-telangiectasia
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23
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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24
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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25
What are the different causes of SCID?
Different causes; affect T & B cell development e.g: - Cytokine receptor defects - RAG defects - Adenosine Deaminase Deficiency
26
How do cytokine receptor defects effect T and B cell development?
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)
27
What is the effect of RAG enzyme defects?
RAG-1/RAG-2 defect => no T and B cells RAG enzymes are involved in TCR + BCR rearrangement RAG defect = no T-cells/B-cells
28
RAG enzymes are involved in .........
TCR + BCR rearrangement RAG defect = no T-cells/B-cells
29
What is the effect of ADA deficiency?
ADA deficiency = deoxyadenosine & deoxy-ATP accumulate = toxic for rapidly dividing thymocytes
30
How is SCID investigated?
Lymphocyte subsets - T, B, NK (% and numbers) => low total lymphocyte count Pattern: - T v.low/absent - B normal/absent sometimes NK also absent (γ-chain defect affecting IL-15 receptor) - Igs low - T cell function ↓ (proliferation, cytokines)
31
How is SCID treated?
- Isolation - Do not give live vaccines ! - Blood products from CMV -ve donors - IV Ig replacement - Treat infections - Bone marrow/HSC Transplant - replenish BM with precursors w/o the mutation - Gene therapy (for ADA and γ-chain genes)
32
Describe SCID prognosis and survival is dependent on .............
Dependent on promptness of diagnosis
33
What is DiGeorge syndrome?
Complex array of developmental defects Affects thymus - thymic hypoplasia chr22q11 deletion Cardiac issues
34
What are the physical signs of DiGeorge syndrome?
Dysmorphic face: cleft palate, low-set ears, fish-shaped mouth
35
What are the clinical symptoms of DiGeorge syndrome?
Hypocalcaemia, cardiac abnormalities Variable immunodeficiency (absent/reduced thymus => affects T cell development)
36
What is Wiskott-Aldrich SYndrome (WAS)?
X-linked Defect in WASP (protein involved in actin polymerisation => T-cells incorrectly model actin cytoskeleton = incorrect signalling)
37
What are the clinical signs of Wiskott-aldrich syndrome?
Thrombocytopaenia, eczema, recurrent infections
38
Describe the progression of Wiskott Aldrich syndrome?
Progressive immunodeficiency (T cell loss) Progressive ↓ T cells; ↓ T cell proliferation Ab production (↓ IgM + IgG; ↑ IgE + IgA)
39
Innate immunity defects involve which progenitor of haematopoiesis?
common myeloid progenitor (differentiates into macrophages + neutrophils)
40
What are the 2 types of innate immunity defects?
- Phagocyte defects | - Complement defects
41
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
42
What are the types of phagocyte defects?
Quantitative (↓ number) Qualitative - Chronic granulomatous disease - Chediak-Higashi syndrome - Leukocyte adhesion defects (LADs)
43
What is chronic granulomatous disease?
Defective oxidative killing of phagocytosed microbes; mutation in phagocyte oxidase (NADPH) components - Formation of granulomas (wall off microbes) chronic granulomatous disease = phagocytosis defect. no destruction of pathogen by phagolysosome = pathogen resides in phagolysosome patients form granulomas = immune attempt to surround the infection, areas full of macrophages unable to clear the pathogen = keep it there
44
How is chronic granulomatous disease diagnosed?
Diagnosis: Tests that measure oxidative burst: - NBT test (nitroblue tetrazolium reduction) - Flow cytometry assay dihydrorhodamine
45
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
46
How is a dihydrorhodamine assay used to diagnose chronic granulomatous disease?
Cells producing active oxygen species will cleave the dye making the cells fluoresce, if deficient no fluorescence will occur Takes ~30 mins
47
What is Chediak-Higashi Syndrome?
- rare genetic disease - defect in LYST gene (regulates lysosome traffic) - neutrophils have defective phagocytosis - no phagosome-lysosome fusion = large granules - repetitive, severe infections
48
What is the role of the LYST gene?
Regulates lysosome traffic
49
What causes recurrent infections in chediak-higashi syndrome?
Defect phagosome-lysosome fusion => defective killing of phagocytosed microbes => recurrent infections
50
How is Cjhediak-Higashi Syndrome diagnosed?
- Necreased number neutrophils | - Neutrophils have giant granules
51
What defects cause LAD (Leukocyte Adhesion Deficiency)?
- Defect in β2-chain integrins (LFA-1, Mac-1) | - Defect in sialyl-Lewis X (selectin ligand)
52
Describe the presentation of leukocyte adhesion deficiency
Skin infections, intestinal + perianal ulcers
53
How is leukocyte adhesion deficiency investigated?
↓ neutrophil chemotaxis | ↓ integrins(adhesion molecules) on phagocytes (flow cytometry)
54
What is the effect of complement deficiencies?
Can affect different complement factors severe/fatal pyogenic infections (C3 deficiency) Predisposition to infection with different pathogens
55
What are the symptoms of complement deficiencies?
Symptoms differ depending on C factor affected
56
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)
57
What is Hereditary angioneurotic oedema?
Failure to inactivate complement (deficiency in C1 inhibitor); intermittent acute oedema skin/mucosa => vomiting, diarrhoea, airway obstruction
58
How are complement deficiencies investigated?
- measure individual components | - complement function: CH50 (haemolysis)
59
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
60
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 ```
61
Outline common secondary immunodeficiency infections
Viral: - HIV, CMV, EBV, - Measles - Influenza Chronic bacterial: - TB - Leprosy Chronic parasitic: - Malaria - Leishmaniasis Acute bacterial - Septicaemia
62
What malignancies cause immunodeficiency?
- Myeloma - Lymphoma (Hodgkin’s, non-Hodgkin’s) - Leukaemia (acute or chronic)
63
What are the age extremities causing immunodeficiency?
prematurity | old age
64
How does prematurity cause immune vulnerability?
- infants < 6 months => maternal IgG | - premature delivery: interrupts placental transfer of IgG => infant Ig deficient
65
How does old age affect the immune system?
Decline in normal immune function
66
T-cell defects often impair .......
B-cell function/Ab production = Combined immunodeficiency | T-helper cells aid B-cells - TH2 cells, TFH cells
67
Selective IgA deficiency IgA =
IgA = mucosal Ig - respiratory tract, urogenital tract, GI tract -low serum + secretory IgA
68
PID Treatment - Stem Cell Gene Therapy
- Extract BM cells from patient - Separate immune cell progenitors - Insert normal gene via virus vector - Reinsert stem cells into patient
69
HIV infection depletes ......
CD4+ T-cells
70
Blood cancer metastases deplete .....
leukocytes
71
HIV is a .....virus that infects ......... cells, causing their ...........
- retro - CD4+ T - depletion When APCs(dendritic cells) bind to T-cell, transfers HIV particles to T-cells
72
Which infections are commonly associated w AIDS?
- Parasites - Toxoplasma - Intracellular bacteria - Mycobacterium TB - Fungi - Viruses
73
What does HAART do?
Highly Active Anti-Retroviral Therapy Stops HIV progressing to AIDS

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