CD Markers Expression on B Cells

Key takeaways

• CD19 and CD20 are not interchangeable. CD19 appears early and persists at reduced level into plasma cells; CD20 appears later and is lost on plasma cells. That single difference explains why anti-CD20 therapy spares antibody-secreting cells.
• Immature B cells are defined by surface IgM. Successful heavy and light chain rearrangement producing surface IgM is what makes a cell immature rather than pre-B.
• CD34 is a progenitor marker and is lost well before the immature B cell stage — it should not appear in an immature B phenotype.
• CD27 is the canonical human memory B cell marker. Any memory B panel without it is incomplete.
• Marginal zone and germinal centre B cells are CD23-low or negative. CD23 is a follicular B cell marker, and it is how follicular and marginal zone cells are separated.
• B2 cells are the conventional follicular population; B1 cells are the innate-like, self-renewing subset found mainly in serosal cavities. The naming is counterintuitive and frequently inverted.
• Kappa versus lambda light chain ratio is the practical test for clonality — a skewed ratio suggests a monoclonal population.

Contents

• What CD markers are
• The core B cell markers
• Markers through B cell development
• Mature B cell subsets
• B1 and B2 cells
• A gating strategy
• Clonality and light chain restriction
• Clinical immunophenotypes
• Controls
• Choosing antibodies
• Frequently asked questions

B cell marker antibodies

Pan-B identification, the memory marker, and the plasma cell markers — covering every stage in the tables below.

CD19

Purified Anti-Human CD19 Antibody [HI19a]

PurifiedHuman

The most reliable pan-B marker — present from pre-B through to plasma cells, where it falls but persists.

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CD20

PE Anti-Human CD20 Antibody [2H7]

PEHuman

Appears later than CD19 and is absent from plasma cells; the target of anti-CD20 therapy.

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CD27

PE Anti-Human CD27 Antibody [O323]

PEHuman

The canonical human memory B cell marker, separating memory from naive within the CD19-positive gate.

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CD38

Biotin Anti-Human CD38 Antibody [HIT2]

BiotinHuman

High on germinal centre B cells and plasma cells; with CD24 it defines the transitional population.

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CD138

CD138 / Syndecan-1 Rabbit Polyclonal Antibody

Rabbit pAbWB / IHC

The definitive plasma cell marker, used to identify them in tissue and marrow.

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CD22

Human CD22 ELISA Kit

Sandwich ELISAHuman

An inhibitory co-receptor restricted to the B lineage, measurable in soluble form.

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What CD markers are

CD stands for cluster of differentiation — a naming system agreed internationally so that a surface molecule recognised by several different antibodies gets one number rather than several competing names. The number reflects the order of assignment, not function or relatedness.

For B cells the practical value is that the marker profile changes predictably with developmental stage and activation state, so a panel of four or five antibodies can place a cell precisely in the lineage.

The core B cell markers

Why CD19 and CD20 are not interchangeable

Both are described as pan-B markers, but their windows differ at the ends of the lineage and the difference is clinically decisive.

CD19 appears early, is retained through differentiation, and remains detectable at lower density on plasma cells. CD20 appears somewhat later and is lost as cells become plasma cells.

The consequence: anti-CD20 depletion removes naive, memory and most mature B cells but leaves plasma cells untouched — so existing antibody titres persist. Anti-CD19 approaches, including CAR-T, reach further along the lineage. Choosing between them is a decision about which populations are meant to survive.

Markers through B cell development

Two corrections to values that circulate widely. CD34 belongs at the progenitor stage only and should not appear in an immature B phenotype. And CD28 is a T cell costimulatory receptor — it appears on plasma cells in some contexts, notably myeloma, but is not part of the immature B profile.

Most importantly, immature B cells are defined by surface IgM. Any description saying IgM is absent at this stage has the defining feature backwards.

Mature B cell subsets

The CD23 pattern is worth stating plainly because it is often listed incorrectly. CD23 is a follicular B cell marker. Marginal zone and germinal centre B cells are CD23-low or negative, and that is precisely how they are separated from the follicular population.

Likewise, memory B cells without CD27 in the panel cannot be reliably distinguished from naive cells — CD20 and CD40 alone do not do it, since both are present on naive B cells too.

B1 and B2 cells

The numbering here is counterintuitive and frequently reversed, so it is worth being explicit.

So B2 is the conventional subset, not B1. The reverse assignment appears often enough that it is worth checking whenever the terms are used.

A gating strategy

Including CD3 in the same plot as CD19 is a small but useful habit — it confirms the B gate is clean rather than merely assuming it.

Clonality and light chain restriction

A point absent from most marker lists but central to why B cell immunophenotyping is done clinically at all.

Each B cell expresses either a kappa or a lambda light chain, never both. A normal polyclonal population shows a kappa:lambda ratio of roughly 2:1. A markedly skewed ratio, or a population expressing only one light chain, indicates clonality and therefore a likely neoplastic process.

No surface marker identifies a malignant B cell directly. Light chain restriction is the readout that distinguishes an expanded reactive population from a clonal one, which is why anti-kappa and anti-lambda are standard in diagnostic B cell panels.

Clinical immunophenotypes

Research and educational context only — diagnostic interpretation belongs with a qualified pathologist.

Controls

• FMO controls for each marker, which set gates correctly by accounting for spillover from every other channel in the panel.
• Viability dye, since dead cells bind antibody non-specifically and generate false positives.
• Single-stained compensation controls, using the same fluorophores as the panel.
• A known-positive sample — peripheral blood contains all the major B subsets and makes a convenient reference.
• Fc receptor blocking where myeloid cells are present, as their Fc receptors bind antibody irrespective of specificity.

Frequently asked questions