Positive selection from newly formed to marginal zone B cells depends on the rate of clonal production, CD19, and btk

Using immunoglobulin heavy chain transgenic mice, we show that B cell clone s reaching the long-lived pool are heterogeneous: some are enriched in the CD21(high) compartment (mostly marginal zone [MZ]), others reside primarily in the follicles (FO). Altering the composition of the B cell receptor thr ough N region additions decreases the rate of clonal production and the MZ enrichment. This process can be recapitulated by purified CD21(low) B cells and is due to a preferential clonal survival that requires a functional bt k tyrosine kinase, We also show that generation of the MZ population is dep endent on CD19. These findings suggest that the MZ B cell repertoire is pos itively selected and have functional implications for antigenic responses e ffected by B cells from this microenvironment.