Development and function of B-1 cells.

Results from immunoglobulin-transgenic mice and BCR-mutant mice have been widely interpreted in recent years as supporting a simple 'activation' model for the origin of CD5+/B-1 B cells. However cell transfer experiments over 10 years ago and recent work investigating pre-BCR signaling suggest striking differences between B cell development in fetal liver and adult bone marrow, lending support for a 'lineage' model that we favor. Recent progress has been made relating to the development and function of the CD5+/B-1 B cell subpopulation in mice; the data can be viewed in the context of the generation of this subpopulation by a distinctive fetal B cell developmental process.