Imm - inborn errors of immunity Flashcards
Give examples of immune disorders that involve phagocytes
Neutrophil deficiency:
- Chronic benign neutropenia
- Familial (idiopathic) neutropenia
- Severe congenital neutropenia
- Reticular dysgenesis
Neutrophil migration/function:
- Leukocyte adhesions deficiency
Generation of reactive oxygen species (ROS)/failure of oxidative killing mechanisms:
- Chronic granulomatous disease
Describe chronic benign neutropenia
Disorder of neutrophil deficiency
Mild/moderate neutropenia
Common in number of ancestry groups (Africa, Middle East)
SNP in DARC gene → absent expression
Asymptomatic (Usually does not need further investigation )
Describe Familial (idiopathic) neutropenia
Disorder of neutrophil deficiency
Moderate/severe neutropenia
Adult onset
Associated with organ-specific autoimmune disease
No significant increase in infection risk
Describe severe congenital neutropenia and what is the treatment
Disorder of neutrophil deficiency and maturation
presents <3 months
Cyclic neutropenia (normal and low): neutrophil elastase (ELA-2) mutation
Includes genetic syndromes e.g. neutrophil elastase, Kostmann (HCLS-1associated protein X mutation), SDS, MDS, AML
Susceptible to oral, cutaneous and epithelial Staph aureus, G- enteric bacteria and fungal infection
Tx: G-CSF support and stem cell transplantation for high risk individuals
Describe chronic granulomatous disease
Failure of oxidative killing mechanisms of phagocytes (respiratory burst)
Deficiency in one of the NADPH oxidase components → inability to generate oxygen-free radicals → impaired killing
NADPH: increased NF-κ β and IL-1β activation
What investigations are treatment are indicated for chronic granulomatous disease
Negative Nitro-Blue Tetrazolium test (NBT). NBT is a dye that changes colour from
yellow to blue following interaction with hydrogen peroxide (free radical)
Dihydrorhodamine (DHR) flow cytometry test. DHR is oxidized to rhodamine, which is
strongly fluorescent, following interaction with hydrogen peroxide.
Management
Cotrimoxazole and itraconazole prophylaxis
Adjunctive IFN-gamma, Stem cell and gene therapy
Describe leukocyte adhesion deficiencies
Failure of neutrophil migration
Deficiency of CD18 (β2 integrin subunit) which (along with CD11a) is expressed on neutrophils → binds to ligand (ICAM-1) on endothelial cells to regulate migration
Lack of adhesion molecule expression → failure to exit the bloodstream
Describe reticular dysgenesis
Failure of stem cells to differentiate along myeloid or lymphoid lineage
Failure of production of: Neutrophils, Lymphocytes, Monocyte/macrophages, Platelets
Fatal in very early life unless corrected with bone marrow transplantation
Autosomal recessive severe SCID (most severe form)
Mutation in mitochondrial energy metabolism enzyme adenylate kinase 2 (AK2)
What are the types of immune disorders that involve complement
Protein deficiency:
Classical pathway
Alternative pathway
C3
Terminal complement pathway deficiency
Mannose-binding lectin (MBL) deficiency
Regulatory proteins:
C1 inhibitor deficiency
Factor H, I, MCP (CD46)
CD55 and CD59
What are the features of early classical complement protein deficiencies and what does it predispose to
(C1/2/4)
- immune complexes fail to activate the complement pathway → increase susceptibility to infection
- Increased load of self-antigens (esp. nuclear components) → promotes auto-immunity and immune complexes
- Deposition of immune complexes → stimulates local inflammation
Predisposes to: SLE (C1/2), encapsulated bacterial infections, Hib, Strep. pneumoniae, skin disease
What is the cause secondary classical complement protein deficiencies
caused by active lupus, due to persistent production of immune complexes and consequent depletion of complement
What are the features of immune disorders involving the alternative complement pathway
Factor B/ Factor D/ Factor P (properdin) deficiency - rare
Inability to mobilise complement rapidly in response to bacterial infections → Recurrent
infections with encapsulated bacteria
Normally properdin stabilizes C3 convertase → triggers MAC complex
Predisposes to neisseria meningitis infection
What are the features of immune disorders associated with primary C3 deficiency
Severe susceptibility to bacterial infections (esp. encapsulated – meningococcus, streptococcus, haemophiles) AND connective tissue disease
What are the features of immune disorders associated with secondary C3 deficiency
nephritic factors (auto-Abs directed against the complement pathway) → stabilises C3 convertases → C3 activation and consumption
Associated with glomerulonephritis (membranoproliferative) and partial lipodystrophy
What are the features of immune disorders associated with Terminal complement pathway deficiency and what does it predispose to
Inability to make membrane attack complex → Inability to use complement to lyse encapsulated bacteria
Predisposes to: N. meningitis, S. pneumonia, H. influenza
What are the features of immune disorders associated with Mannose binding lectin deficiency
Not clinically significant, 5-30% of population
Associated with increased infection in patients who have another cause of immune impairment
- Premature infants
- Chemotherapy
- HIV infection
- Antibody deficiency
What are the features of immune disorders associated with C1 inhibitor deficiency
Recurrent episodes of bradykinin-mediated angioedema (skin, abdomen, larynx)
Low C4, Normal C3
Tx: Emergency therapy with C1 inhibitor (not adrenaline) and maintenance therapy with C1 inhibitor concentrate
What are the features of immune disorders associated with Factor H, I, MCP (CD46)
C3 glomerulopathy
Atypical Haemolytic uraemic syndrome
Low C3 normal C4 absent alternative pathway function (AP50)