Definition:
As well as B-lymphocytes as T-lymphocytes originate in the hematopoietic stem cell. Only the first stages of B-lymphopoiesis occur in bone marrow. The first cells are pro-B-cells. They develop via pre-B-cells to immature B-cells, who leave the bone marrow in order to become immunologically mature in peripheral lymphatic organs (spleen, lymph nodes, tonsils, Peyer's patch, etc.) During early B-cell development in the bone marrow, the rearrangement of V-, D- and J-gen fragments to complete heavy chain and light chain gens occurs (VDJ-rearrangement). The early B-cell-stages are immature, blastic cells and are also called hematogones. Normally, these cells are very rare and do not stand out. In some states, e.g. after chemotherapy, their number can be increased and have to be differentiated from leukemic blasts.
The first development of T-lymphocytes occurs in the thymus. The later immunologic maturation occurs in peripheral lymphatic organs (spleen, lymph nodes, tonsils, Peyer's patch, etc..
Most lymphocytes in the bone marrow are small and mature. These are immunocompetent cells that have undergone immunologic maturation and returned to the bone marrow.
Lymphopoiesis:
Lymphoblast --> lymphocytes --> plasma cells