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Luke Droney
Memory B cells Explain the process of B-‐cell memory immunophenotyping and its diagnostic and management implications for CVID Flow for memory Bs uses three significant markers:
• CD27 (+ve -‐ memory marker) • CD21 (+ve with maturation) • IgD neg/IgM neg (defines isotype switched)
The ‘Freiburg’ classification defines two main groups:
1. Reduction of isotype-‐switched memory B cells (CD27+/IgM-‐/IgD-‐) – expressed as percentage of lymphocytes
2. Normal memory B cells Group 1 is further divided: 1a. Increased proportion of naïve B cells 1b. Normal proportion of naïve (CD21-‐) B cells Reference ranges suggested by the Freiburg classification and confirmed in subsequent studies:
• Memory Bs >0.4% of peripheral blood lymphocytes • CD21-‐ B cells <20% (expressed as a percentage of total B cells)
Or represented graphically in the Westmead cohort:
There’s also the ‘Paris’ classification:
1. MB0: reduced memory B cells (as a proportion of total B cells)
Luke Droney
2. MB1: normal levels of non-‐isotype switched memory B cells (IgD+/CD27+) but deficient switched memory B cells
3. MB2: normal memory B cells Represented graphically, thanks to Westmead again:
Process: Flow with the following markers:
• CD19 • CD21 • CD27 • CD20 • IgD
Analysis – Path QLD plots:
Luke Droney
Results from studies:
• The Freiburg classification found an increased occurrence of splenomegaly and autoimmune cytopaenias in group 1a.
• Paris classification showed increased incidence of splenomegaly, lymphoproliferation and granulomatous disease in MB0, increased splenomegaly in MB1 but equal prevalence of autoimmunity in all three groups.
• The Westmead cohort showed: o Increased splenomegaly, lymphadenopathy, autoimmune cytopaenias
in Freiburg 1a group c.f 1b and 2. o Paris classification was not as useful. MB2 were less likely to display
lymphoproliferation and cytopaenias. o Increased immature B cells were associated with lymphoproliferation
and autoimmune cytopaenias. • A French study (Mouillot et al J Clin Immunol 2010) in a cohort of 313 with
CVID showed: o Decreased switched memory B cells in patients with ‘infection only’
but more marked defects in patients affected by lymphoproliferation, autoimmune cytopaenias and chronic enteropathy.
o Patients with these manifestations were also more likely to have an increase in CD21-‐ B cells.
o In this study there was no link between transitional B cells (IgM++/CD38++) and clinical phenotype.
o (Patients with the above manifestations also had a more marked decrease in naïve CD4+ and CD8+ T cells, an increase in activated T cells and a decrease in T regs)
Luke Droney
• A French study published in 2008 (same cohort) (Oksenhendler et al) demonstrated that patients with switched memory Bs <2% of total B cells had an increased requirement for antibiotics and were more likely to progress to bronichectasis.
• Patients with decreased non-‐switched (IgD+) memory B cells have impaired IgM responses to polysaccharide pneumococcal vaccine and increased risk of pneumococcal pneumonia.
• As an aside, post-‐splenectomy patients commonly display a reduction in non-‐switched memory B cells and looking for this reduction may select a sub-‐group of patients whom benefit most from antibiotic prophylaxis
Therefore I would say that the clinical utility of B-‐cell immunophenotyping in CVID is:
• To identify a subset of patients with reduced switched memory B cells that have been demonstrated to have an increased risk of splenomegaly and lymphadenopathy.
• These patients also have a greater requirement for antibiotics and are more likely to progress to bronchiectasis.
• Patients with reduced memory B cells also have an increased risk of granulomatous disease.
• An increase of CD21 -‐ B cells (both Freiburg group 1 and group 2) has been associated with autoimmune cytopaenias and lymphoproliferation.
Other:
• A marked reduction in switched memory B cells is seen in XLP and X-‐linked hyper-‐IgM syndrome. i.e male patients in Freiburg 1 group should have these excluded.
• The observed increased CD21-‐ immature B cell population may represent a subset of chronically activated B cells that contribute to autoimmunity – similar to SLE.