PreB

PreB, or pre-B cell, refers to a defined stage in B lymphocyte development that occurs in the bone marrow. It follows the pro-B cell stage and precedes the immature B cell stage. At this point, B cells have rearranged the immunoglobulin heavy chain gene and express the μ heavy chain in combination with a surrogate light chain to form the pre-B cell receptor (pre-BCR). Signaling through the pre-BCR promotes clonal expansion, enforces allelic exclusion of heavy chain genes, and initiates the next phase of development, which is light chain rearrangement.

Development and lineage progression hinge on the formation of the pre-BCR. The receptor comprises the μ heavy chain paired with surrogate light chains, VpreB and λ5, and signals through associated Igα/Igβ components. This signaling drives proliferation and advances cells from the large pre-B stage to the small pre-B stage, the latter of which reduces proliferation and begins rearrangement of light chain genes. Successful light chain rearrangement results in surface expression of a complete B cell receptor consisting of surface IgM, marking the transition to the immature B cell stage.

Phenotype and markers are used to identify pre-B cells in research and clinical contexts. Pre-B cells typically do not display a mature surface immunoglobulin, though they contain intracellular μ heavy chain and surrogate light chains. They express common B cell markers such as CD19 and CD79 and are associated with B220 lineage markers; the pro-B to pre-B transition is often accompanied by downregulation of CD43. Large pre-B cells are highly proliferative, while small pre-B cells are transitioning toward light chain recombination and maturation.

Clinical relevance centers on the pre-B cell stage as the cell of origin for certain leukemias, notably pre-B acute lymphoblastic leukemia. Malignant cells at this stage commonly express B cell–associated markers (for example, CD19) and other lineage markers used in diagnostics and treatment planning.