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FPP: pre-midterm > Primary Immune Deficiencies > Flashcards

Primary Immune Deficiencies Flashcards

1
Q

What are primary immune deficiencies?

A

PIDs; intrinsic defects in the immune sysemt (usually but not always inherited)

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2
Q

What are secondary immune deficiencies?

A

Due to extrinsic factors that depress the immune response

  • infections (HIV, measles)
  • malnutrition
  • malignancies (lymphoma, leukemia)
  • metabolic (diabetes, liver disease)
  • loss of lymphocytes/Abs
  • immunocuppressants (corticosteroids, rituximab)
  • collagen vascular disease
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3
Q

When should you suspect a PID?

A
  • Too many infections or infections that won’t go away
  • Weird infections (e.g. P jerovecii)
  • Infections in weird places (e.g. liver/lung abscesses)
  • Early onset autoimmunity
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4
Q

What cell expresses CD3+/CD45RA+?

A

Naive T cell

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5
Q

What cell expresses CD3+?

A

All T cells

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6
Q

What cell expresses CD3+/CD45RO+?

A

Memory T cell

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7
Q

What cell expresses CD3+/CD4+?

A

Helper T cell

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8
Q

What cell expresses CD3+/CD8+?

A

Cytotoxic T cell

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9
Q

What cell expresses CD19+/CD20+?

A

All B cells

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10
Q

What cell expresses CD3-/CD56+?

A

NK cell

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11
Q

What are the common characteristics of neutrophil defects?

A
  • Early onset (infancy/childhood)
  • Severe bacterial infections and abscesses
  • Poor wound healing with lack of pus

E.g. Chronic granulomatous disease, congenital/cyclic neutropenia, or leukocyte adhesion deficiency

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12
Q

How do you workup a neutrophil defect?

A
  1. CBC (complete blood count) with differential
    *Note ANC (absolute neutrophil count)
  2. DHR (dihydrorhodamine test)
    *tests ability of PMNs to generate oxidative burst
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13
Q

What are the common characteristics of complement defects?

A
  • Present at any age
  • Early (C2, C4) defects
    • autoimmune presentation most common (e.g. lupus)
    • sinopulmonary infections, sepsis
      *S. pneumoniae and H. influenzae
  • Late (C5-C9) defects
    • increased susceptibility to Neisserial infections
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14
Q

How do you workup a complement defect?

A

CH50 test (functional assay for all classical complement components… CH50= 0)
**If problems with complement consumption (lupus) the CH50 is low

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15
Q

What is the most common PID type?

A

B cell/Antibody deficiencies

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16
Q

What are the common characteristics of an antibody deficiency? Examples?

A
  • Recurrent sinopulmonary bacterial infections
    **encapsulated organisms (H. flu, S. pneumo, Mycoplasma)
  • Chronic GI tract infections, malabsorption, failure to thrive

Examples:

  1. XLA (agammaglobulinemia) *early presentation
  2. CVID *presents at any age
17
Q

How do you workup an antibody deficiency?

A
  1. Quantitative immunoglobulins (IgG/A/M/E)
  2. Vaccine titers (diptheria, tetanus, pneumococcus)
    *If titers are low, re-immunize and remeasure after 4 weeks to double check

**Don’t forget to consider a secondary cause (immune suppressing drugs) if workup looks positive!

18
Q

What are the common characteristics of T cell defects?

A
  • Recurrent, sever infections
    • Viruses (CMV, EBV, varicella)
    • Fungi (oral candida/thrush)
    • Bacteria
    • Opportunistic pathogens (P. jiroveci, mycobacteria)
  • Poor growth/FTT
  • Chronic diarrhea

**e.g. DiGeorge syndrome

19
Q

How do you workup a T cell/combined defect?

A
  1. CBC with differential
    **Low ALC (absolute lymphocyte count)
  2. Lymphocyte subset enumeration (flow cytometry)
    1. T(memory and naive)/B/NK cell numbers
    2. Quantitative Igs (G,M,A)
    3. T cell proliferation
20
Q

What is a common B/T cell combined deficiency?

A

SCID

21
Q

What are the common symptoms of SCID?

A
  • Onset in infancy (otitis media, thrush, diarrhea, FTT)
  • Opportunistic pathogen infection (e.g. P. jiroveci)
    **Lack T/NK cells, B cells present but don’t function
  • Most commonly X-linked (mutation in gamma chain of IL2 receptor)

**100% mortality without bone marrow transplant

22
Q

What is the screening test for SCID?

A
  • TRECs (T cell Receptor Excision Circles; nonreplicating circular pieces of DNA in naive T cells generated in the process of making a TCR)
  • TREC number (measured by RT-PCR) is a surrogate marker for the number of normal naive T cells
  • T cells/TRECs low in all forms of SCID and T cell lymphopenias
23
Q

What does the CATCH22 mnemonic stand for?

A

The wide clinical spectrum of DeGeorge syndrome:

  • Cardiac defects
  • Abnormal facies
  • Thymic hypoplasia
  • Cleft palate
  • Hypocalcemia
  • 22nd chromosome

**many cases undiagnosed until late childhood/adulthood

24
Q

Describe DeGeorge syndrome

A

TBX1 gene deletion from chromosome 22q11.2

*T cell abnormalities also lead to Ab deficiency

**results in field defects of pharyngeal pouches 1-6:

  1. tubotympanic anomalies
    (1st arch: facial anomalies… maxillary/mandible)
  2. tonsil/thyroid anomalies
  3. inferior parathyroid/thymus deficiencies
  4. superious parathyroid
25
Q

Describe XLA symptoms… what mutation causes it?

A

(X-linked Agammaglobulinemia) Commonly observe:

  • onset in infancy/early childhood
  • recurrent otitis, sinusitic, pneumonia
  • encapsulated bacteria (S. pneumo, H. infl) and mycoplasma sp
  • severe enteroviral infections; vaccine related polio

**Caused by mutations in Bruton’s Tyrosine Kinase Gene (Btk) which results in the failure of B cells to differentiate… can diagnose with flow cytometry

26
Q

What lab results would point towards XLA?

A

No B cells present (normal T cells)

Hypogammaglobulinemia

Diffuse bronchiectasis (widening of airway)

27
Q

What lab results would point towards CVID?

A

Bronchiectasis (widening of airway)

Opacification of sinuses/mucosal thickening

Normal T and B cells

Low IgG and no IgA (usually, or low IgA/IgM)

28
Q

Describe CVID

A

**Common variable immunodeficiency

  • Most common PID
  • Onset at ANY AGE with variable clinical course
  • Infections common
  • GI/liver disease (Inflammatory bowel disease)
  • Pulmonary disease (bronchiextasis, interstitial lung disease)
  • ​Autoimmunity (cytopenias)
29
Q

What is the most common Ab deficiency? What are the characteristics/symptoms?

A

**IgA deficiency

  • Extremely low IgA, normal IgG and IgM
  • Normal T cell function
  • Usually no phenotype
    • Some have increased sinopulmonary/GI infections
  • Increased incidence of atopic, celiac and autoimmune disease

***Do not treat with IVIG

30
Q

Describe CGD

A

**Chronic Granulomatous Disease

  • onset usually by 2 yo
  • hepative abscess without obvious source in young child is CGD until proven otherwise
  • pneumonia
  • sepsis
  • osteomyelitis
  • infection with catalase + bacteria (burkholderia, nocardia)
31
Q

What is the cause of CGD?

A
  • Functional absence of respiratory burst in neutrophils and monocytes- impair bactericidal killing
  • Defect in NADPH oxidase (most common= x linked)
32
Q

How does a DHR test work? What is it used for?

A
  • Dihydrorhodamine is oxidized when PMNs are stimulated to undergo oxidative burst (by PMA/phorbol ester)
  • The oxidized form of DHR exhibits increased fluorescence which is seen as a right-shifted peak on flow cytometry post-burst
  • Carriers will have two peaks (one normal, one shifted pos-burst) -> at risk for autoimmune disease

**used to diagnose neutrophil disorders (e.g. CGD)

33
Q

Describe late complement deficiency

A
  • Cannot form MAC (lack C5-9)
  • First infection usually ~17 yo
  • Recurrent meningitis (but lower fatality from it)
    *susceptible to all neisseria including gonorrhea
34
Q

Describe early complement deficiency

A
  • C2= most common deficiency (autosomal recessive)
  • Associated with collagen vascular diseases
  • Recurrent bacteremia (pnemo, flu, enteric, staph)

FPP: pre-midterm (19 decks)

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