From Bone to Flow: Comprehensive Flow Cytometry Protocol for Profiling B Cell Populations in Mouse Bone Marrow v1

B cell subsets in murine bone marrow play diverse roles in immune function and disease, making their identification and characterization essential. Flow cytometry enables effective discrimination between these subsets using specific surface markers. This protocol describes the use of key markers—B220, CD45, CD19, IgD, IgM, and CD43—to identify and analyze B cell populations. B220, a pan-B cell marker, plays a critical role in distinguishing between the various maturation stages of B cells. It is particularly useful for tracking the transition of B cells from precursors to mature forms (Bleesing & Fleisher, 2002). CD45, another significant marker, is used to differentiate stages within the B cell lineage, providing insights into memory cell formation in mice (Bleesing & Fleisher, 2002). CD19 is a consistent marker expressed across different B cell stages and is essential for initiating signal transduction, which is crucial for B cell activation and development (Sato et al., 2004). Accurate identification of B cells in the bone marrow requires the use of B cell-specific molecules, CD19 and/or B220, as surface markers. B220 and CD19 are present on the surface of all later-stage B lineage cells, except for a subpopulation of terminally differentiated plasma cells. To further differentiate B cell developmental stages, pre-pro B cells, pro-B cells, and pre-B cells are defined based on their distinct expression patterns of CD43. IgD and IgM are pivotal in identifying naive and early B cell stages, where IgM is generally expressed initially, followed by IgD expression during the maturation process. Their combined use facilitates the identification of transitional stages within the B cell lineage (Sato et al. 2004). Finally, CD43 expression is notably valuable for distinguishing B-1 cells, which differ from conventional B cells by being predominantly expressed in distinct subsets, such as those in the spleen (Wells et al., 1994). This method provides a comprehensive approach to delineate B cell subset dynamics, summarizing and streamlining the experimental steps and data interpretation to facilitate its application across different studies, contributing significantly to the understanding of immune regulation and potential alterations leading to disease.