3.1.4 Transition from immature B-cell to mature B-cell

The immature B-cell leaves the bone marrow parenchyma and passes through an endothelial barrier and enters the blood sinusoids, where they are retained, before finally being released into the peripheral blood [29], which allows them to migrate to the spleen where they complete their development [30]. The transition from the immature B-cell to the mature B-cell takes place in a few days and leads, via alternative splicing of long primary mRNA transcripts from the IG heavy (IGH) locus [31], to the coexpression on naïve mature B-cells of membrane IgM and IgD that share the same antigenic specificity. Only about 5% of immature B-cells will sustainably give rise to peripheral B-cells; however, most newly formed ones disappear within a few days.
