What are the steps of B cell maturation?

The maturation of B cells occurs over several key steps:

1. B cells originate from hematopoietic stem cells (HSC) in the bone marrow, which is the primary site of development.
2. The hematopoietic stem cells divide to form lymphoid progenitor cells.
3. The progenitor cells differentiate and specialize into Pro-B cells (progenitor-B cells), which multiply inside the bone marrow and develop into Pre-B cells (precursor-B cells). The bone marrow stromal cells secrete IL-7 (interleukin-7) and other cytokines that support the development of pro-B cells to pre-B cells.  
4. As the pre-B cells develop further, they begin expressing CD25, a component of the IL-2 receptor. 
5. The IL-7 released by stromal cells, which drives the maturation process, leads to the eventual reduction of adhesion molecules on Pre-B cells, resulting in the detachment of the proliferating cells from stromal cells. 
6. The Pre-B cells undergo a genetic rearrangement of the light chain to transition to the next stage and become immature B cells. 
7. Immature B cells undergo two selection processes – positive selection and negative selection. Immature B cells with receptors that react too strongly with self-antigens are eliminated through apoptosis to prevent the development of self-reactive immune response. Immature B cells that have receptors displaying appropriate self-tolerance are allowed to exit the bone marrow and enter the bloodstream. At this point, they are considered transitional B cells. 
8. Transitional B cells move through the bloodstream to secondary lymphoid organs such as the spleen and lymph nodes where they continue to undergo maturation and await encounters with antigens. 

It takes about 1 to 2 weeks to develop from hematopoietic stem cells to mature B cells.