Comprehensive phenotyping of human peripheral blood B lymphocytes in healthy conditions

Abstract

The B cell compartment provides innate and adaptive immune defenses against pathogens. Different B cell subsets, reflecting the maturation stages of B cells, have noninterchangeable functions and roles in innate and adaptive immune responses. In this review, we provide an overview of the B cell subsets present in peripheral blood of healthy individuals. A specific gating strategy is also described to clearly and univocally identify B cell subsets based on the their phenotypic traits by flow cytometric analysis.

Keywords: B cell subsets; flow cytometry; human B cells; phenotyping.

FIGURE 1

Schematic representation of B cell development in the bone‐marrow and in the peripheral blood. The top part of the figure illustrates the step‐wise development of the cells of the B lineage in the bone marrow. Transitional B cells are generated in the bone marrow, but can be also found in the peripheral blood (lower part of the figure). In the bone marrow B‐cell development is driven and controlled by the rearrangement of immunoglobulin heavy and light chain. In the periphery B‐cell antigen and TLR signals determine the progression to the memory B cells and plasma cells stage. Long‐lived memory plasma cells represent the final stage of B‐cell development and home to a dedicated niche in the bone marrow [Color figure can be viewed at wileyonlinelibrary.com]

FIGURE 2

Total blood of adult (A), 2 days old (B), and 2 months old infant (C) stained with antibodies against CD19, CD24, CD27, CD38, IgM, IgG, IgD, and CD21. Live cells were identified based on FSC/SSC lympho‐monocyte gate and then selected as CD45^posCD19^pos B cells. We identified transitional (CD24^posCD38^bright) and plasmablasts (CD24^negCD38^bright). We showed IgM, IgD, and CD21 expression in transitional B cells (CD21^dull and CD21^bright). In not transitional/not plasmablasts population, we discriminated mature‐naïve (CD24^negCD21^pos), memory (CD24^posCD27^posCD21^pos), atypical memory (CD21^negCD27^neg), and activated B cells (CD21^negCD27^pos). CD27^pos memory B cells can be also divided into CD27^dull and CD27^bright based on CD27 expression. In the CD27^pos memory B‐cell population, we showed IgD^pos and IgD^neg memory B cells. IgD^neg memory B cells were further divided into IgG^pos, IgG^negIgM^neg (that are mostly IgA^pos), and IgM‐only. Among atypical memory B cells, IgM and IgD expression identify different subtypes [Color figure can be viewed at wileyonlinelibrary.com]