IntroductionThe developmental pathways of these cells are very complex and unique but similarities exist. B cells produce antibodies to bind to foreign bodies that have invaded the host organism; this allows cells such as cytotoxic T cells to destroy the infected cell/structure. On the other hand, T cells such as T-helper cells that secrete cytokines to control immune responses and cytotoxic T cells that destroy pathogenic cells and structures. B Cells B cells develop from pluripotent hematopoietic stem cells, which give rise to lymphoid cells. progenitor cells in the bone marrow. These stem cells became Pro-B cells when they began expressing B cell marker proteins such as CD34 and rearranging genes that code for heavy chains in the B cell receptor (BCR). In the next stage of development, Pro-B cells will become Pre-B cells. The transition to Pre-B cells involves the expression of the μ heavy chain on the cell surface. “The RNA transcript is spliced ​​to produce mRNA”[1] to synthesize the μ chain and express it on the cell surface in the Pro-B cell to Pre-B cell stage. Now the Pre-B cell can develop into an immature B cell. BCR light chains must be expressed before the cell can be called an immature B cell. Once this was completed, an immature B cell was produced. Immature B cells play a vital role in preventing autoimmunity. If immature B cells self-react, autoimmunity can arise. These cells would be killed as soon as they come into contact with a self-antigen, since they are self-reactive. Cells with abnormally high autoreactivity are killed via apoptosis before they can enter the general cell population, this is where approximately 90% of cells produced are lost before... middle of paper... Janeway, C 2009. The system immune. 3rd ed. London: Garland Science.2. Nataly Manjarrez-Ordu|[Ntilde]|O, IS 2009. B cells and immunological tolerance. Nature, 129 (2), p. 278. Available from: doi: doi:10.1038/jid.2008.240.3. Kuby, J., Goldsby, R.A., Kindt, T.J. and Osborne, B.A. 2007. Immunology. New York: Freeman.4. Starr, T.K., Jameson, S.C. and Hogquist, K.A. 2003. Positive and negative selection of T cells. Annual review of immunology, 21(1), pp. 139--176.5. Janeway, C. 2001. Immunobiology. New York: Garland Pub.6. Maria Hinterberger, Martin Aichinger, Olivia Prazeres da Costa, David Voehringer, Reinhard Hoffmann & Ludger Klein (2010) 'Autonomous role of medullary thymic epithelial cells in central CD4+ T cell tolerance', Nature Immunology, (), pp. .7. Kuby, J., Goldsby, R.A., Kindt, T.J. and Osborne, B.A. 2007. Immunology. New York: Freemann.