A Guide to B Cell Markers

B cells, or B lymphocytes, are an important and complex cell type that plays central roles in humoral immunity against infections, autoimmunity and transplantation. Their ability to produce clonally diverse cell surface immunoglobulins, or antibodies, that recognize foreign antigens is rooted in complex developmental pathways that allow for immediate and long-lived responses. In addition to antibody-mediated actions, B cells can also drive cellular immune pathways via antigen presentation, T-cell activation, cytokine production, and by acting as regulatory cells. 

Extensive research in mice and humans has led to the identification of unique B cell populations, each with important implications in understanding B cell biology. With each cell subset, corresponding sets of protein markers for detection have been established. In this article, we review common B cell markers that have been recently described.

Image: A simplified summary of prominent B cell subtypes, including a generalized overview of their development and activation.

Markers for B Cell Development

From birth, hematopoietic lymphocyte precursors give rise to the B1 and B2 lineages of B cells. B1 cells originate from the fetal liver and persist as a self-renewing population within the periphery with little connection to the bone marrow in adulthood. B1 cells produce T-independent humoral responses and have been reported to have the phenotype CD20+, CD27+, CD43+, CD70– (in humans).

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B2 cells follow a sequential developmental program within the bone marrow, where the B cell receptor (BCR) develops and the process of central tolerance selects for appropriate B cells.

Collectively, the developmental stages give rise to populations of Pro B, Pre B, and Immature B cells. Markers reported for these stages include CD22, IL7R, CD34, CD38, CD79, and MME. B cells that complete this program make their way toward the spleen in transitional stages (T1, T2, T3) and express CD19+, IgDlo/+, CD27–, CD24++, CD38++.

B cells differentiate further into marginal zone (MZ) B cells or follicular (FO) B cells. MZ B cells in the spleen, which make up to approximately 20% of peripheral human B cells, express polyreactive BCRs and natural IgM antibodies, enabling both T-dependent and T-independent responses. Notable proteins expressed by MZ B cells include CD21 and CD1D. FO B cells, residing in the lymphoid follicles of the spleen and lymph nodes, comprise the most dominant population of this immune cell. Upon acquiring antigens and interacting with follicular T cells, they proliferate within germinal centers (GC), leading to the production of all antibody isotypes and high-affinity antibodies. Some proteins associated with B cells in the GC include FAS, HLA-DR, and BAFF-R (TNFRSF13C).

Markers for Antibody-Secreting Cells

To effectively carry out antibody production, B cells will ultimately differentiate from a naive state into antibody-secreting plasmablasts and plasma cells. These mature, yet unactivated naive B cells may be identified with the phenotype CD19+, IgD+, CD27–, CD38+/–, CD24+/–. 

Plasmablasts are proliferating, short-lived activated B cells that can secrete antibodies while dividing. These mediators of the early antibody response can arise from both T-dependent and T-independent activation. Plasmablast populations can come from B1 cells, MZ B cells, FO B cells, and memory cells, and may further mature into plasma cells. Plasma cells are non-dividing, terminally differentiated B cells that have emerged from matured, activated GC B cells. This population generates large quantities of high-affinity and class-switched diversified antibodies. They are long-lived and migrate to the bone marrow where they survive supported by stromal cells. Plasmablasts and plasma cells express similar proteins and may be identified with the surface marker phenotype CD19+/–, IgD–, CD27++, CD38++, CD24– as well as by the expression of transcription factors BLIMP1, XBP1, and IRF4. In addition, plasma cells express high levels of CD138 (SDC1). 

B cell activation also generates populations of memory B cells, pathogen-experienced cells that can be rapidly reactivated to produce high-affinity antibodies. During a secondary immune response, this long-lived B cell subtype can differentiate back into GC B cells, plasmablasts and plasma cells. Memory B cells can be categorized by expressed immunoglobulin markers, such as IgM+, IgG+, IgA+ and IgE+ memory B cells. A canonical phenotype has been suggested, CD19+, CD27+, CD38+/–, CD24+/–.

Regulatory B Cell Markers

A special category of B cells, known as regulatory B cells (Bregs), have been found to influence a variety of immune system processes, including suppression of inflammation. Bregs appear to be a functional classification, lacking a common phenotype but able to develop various populations of B cells. Some defining characteristics include the production of anti-inflammatory cytokines IL-10 and IL-35, as well as the regulatory molecule PD-L1 (in mice). Other reported Breg markers include CD1D, CD24, CD5, CD44, CD38, and CD71 (TFRC).

Table of B Cell Markers

The table below lists human genes (or proteins*) that have been described as B cell markers in recent literature. While most markers are proteins expressed on the cell surface, other notable types are also included, including transcription factors and cytokines. Listings of relevant antibodies and ELISA kits are associated with each marker, as these immunodetection tools are routinely used in cell characterization studies via flow cytometry and immunostaining. These products come from a variety of reagent suppliers and can serve as a handy reference for B cell marker immunodetection.

Note: *Some proteins are protein isoforms or multi-subunit protein complexes composed of several distinct genes. Information on Protein Type, Localization, and Size (kDa) obtained from UniProt.org.

References

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