Peritoneal and splenic B‐1 cells are separable by phenotypic, functional, and transcriptomic characteristics

B-1 cells constitute a distinct B cell population with unique phenotypic and functional characteristics. Although the origin of B-1 cells remains controversial, B-1 cells in different locations are generally considered to be part of the same pool. To determine the validity of this assumption, we examined peritoneal and splenic B-1 cells isolated by flow cytometric cell sorting from normal mice for several features. We found that splenic B-1 cells differ from peritoneal B-1 cells in terms of surface antigen expression, viability ex vivo, immunoglobulin secretion in vitro, stimulated cell cycle progression, and expression of Notch family, Notch-dependent, and Notch-associated genes. These results indicate that splenic and peritoneal B-1 cells are not the same and thus dispute the notion that B-1 cells are uniform, and may suggest that different subpopulations of B-1 cells arise separately, home individually, and/or are heavily influenced by local environmental factors.