Disease Associations of Cluster of Differentiation (CD) 5+ Peripheral B Cells in a Diagnostic Flow Cytometry Laboratory.

Background: Cluster of differentiation (CD) 5+ B cells comprise approximately 15% of peripheral blood B cells and are commonly encountered in diagnostic flow cytometry. However, their disease associations have not been systematically reviewed before, particularly in non-CD5+ B-cell malignancy cases. The aim of this study was to ascertain the prevalence and clinical associations of nonmalignant-associated peripheral blood CD5+ B cells in the diagnostic flow cytometry laboratory.

Methods: Over a period of 3 months, we undertook a single-laboratory cross-sectional study to examine disease associations of CD5+ B cells. B cells were assessed by flow cytometry using our standard B-cell panel. Medical records were reviewed to ascertain disease associations.

Results: In the audit period, there were 426 consecutive B-cell panels excluding duplicate patients, CD5+ B-cell malignancies, and B-cell-depleted samples. The highest percentage of CD5+ B cells were noted in patients with autoimmune diseases and was, in general, higher than patients who had infections or other hematological disorders.

Conclusions: CD5+ B cells are common in the periphery of patients with a variety of medical conditions and may reflect a degree of B-cell hyperreactivity. It would be important for future studies to examine the functional role and consequences of these B cells, and whether they may hold any prognostic or monitoring value.