Primary Immunodeficiency

Primary Immunodeficiency

·        Most single gene disorders: range of effects e.g. antibody or complement deficiencies

·        Clinical features:

o   Highly suspicious: chronic, recurrent or unusual infections, incomplete response to treatment 

o   Moderately suspicious: skin rash (eczema, candida), diarrhoea, growth failure, recurrent abscesses, hepatosplenomegaly

·        Different infections associated with different disorders 

o   ¯Antibodies: sino/pulmonary/gut problems

o   ¯CMI: multisystem (e.g. CMV), pulmonary (PCP, aspergillus, candida), viruses (e.g. Herpes)

o   Phagocytic problems: s. aureus 

o   ¯Complement: recurrent neisserial infection

·        Symptoms depend on where in the lineage the defect is:

o   Stem cell: eg SCID

o   Pre-B cell: X Linked Agammaglobulinaemia

o   Maturation Defect: eg can‟t switch from IgM to IgG

Group 1 – Combined Variable Immunodeficiencies (CVID)

·        Prevalence 1 in 20 – 50,000

·        Symptomatic at 15 – 35 years (but long diagnostic delay)

·        Recurrent pyogenic problems/autoimmune features/respiratory infections

·        GI infections: giardia, campylobacter, HCV

·        Normal B cells: but defect in maturation – no plasma cells

·        Treatment: iv Ig (e.g. Intragam), prophylactic antibiotics 

·         E.g. x-linked SCID (Severe Combined Immunodeficiency), Adenosine deaminase (ADA) deficiency

Group 2 – Antibody deficiencies

·        Diagnosis of primary antibody deficiencies:

o  Serum Ig‟s

§  Quantitative measurement essential (electrophoresis insensitive)

§  Severe hypogammaglobulinaemia: serum IgG level below 3 g/L in adults

o  Response to vaccination (important test)

§  Tetanus and Pneumo-Vax 

§  Do baseline, vaccinate, expect 4 times ­ at 4 weeks 

o  IgG subclass concentrations: interpretation difficult. Based on lymphocyte count. E.g. if lymphocytes normal then primary, if low lymphocytes then ?SCID

o  Lymphocyte Subsets:

§  Absence of B cells in Brutons

§  CVID: up to 30 % have T cell reductions 

§  CLL - ­CD5+ B cells

·        IgA Deficiency (most common genetic deficiency)

o  Approx 1 in 700 

o  ® Respiratory & GI infections

o  Risk of anaphylaxis with blood products due to reaction to exogenous IgA

o  Don‟t treat with Ig

o  Runs in families with CVID

o  Can be associated with:

§  IgG subclass abnormalities

§  Impaired responses to vaccination

Group 3 – Immunodeficiency associated with other defects Group 4 – Complement deficiencies

·        Opsionisation: attachment of C3 to immune complexes 

·        ¯C3 ® pyogenic infections due to ¯ lysis

Group 5 – defects of phagocytic number or function

·        E.g. severe congenital neutropenia, chronic granulomatous disease, IFN gamma receptor deficiency

·        Can test for chemotaxis, adherence and phagocytic function

·        Management: specific antibodies, G-CSF in neutropenia, etc