16.3 Development of B lymphocytes

The precursor cells formed from the bone marrow stem cells are called pro-B cells . The pro-B cells do not express any antibody. Recombination process of Ig chains starts during pro-B cell stage because of the expression of Rag gene. Once the V (D) J recombination of heavy chain is completed, the pro-B cell is differentiated into pre-B cells . Pre-B cell expresses the heavy chain of the Ig over their surface and are identified by the presence of B220 surface markers. Pre-B cells are differentiated into immature B cells after the synthesis of light chains of the Ig over their surface. The immature B cells are differentiated into mature B cells after the synthesis of mature IgM and IgD molecules over their surface.

16.4 Development of T lymphocytes

The precursor stem cells in the bone marrow are differentiated into pro-T cells into thymus. The pro-T cell is differentiated into pre-T cell with the recombination of β chain. The pre-T cell express only the β chain of T cell receptor that further differentiates into double positive T cells which expresses both α and β chain over the surface. In addition double positive T cell expresses both CD4 and CD8 over their surface. The double positive T cells undergoes positive and negative selection to differentiate into immature T cells that express membrane associated α and β chain. The immature T cells are differentiated into mature T cells after coming into the peripheral circulation.