B Cells



To: -----------Manager/Supervisor

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Date: October 13, 2009

Subject: B Cells

Introduction

B cells are lymphocytes that play a large role in the humoral immune response (as opposed to the cell-mediated immune response, which is governed by T cells). The principal functions of B cells are to make antibodies against antigens, perform the role of Antigen Presenting Cells (APCs) and eventually develop into memory B cells after activation by antigen interaction. B cells are an essential component of the adaptive immune system.

B Cells

The abbreviation "B", in B cell, comes from the bursa of Fabricius in birds, where they mature. In mammals, immature B cells are formed in the bone marrow. Immature B cells are produced in the bone marrow of most mammals. Rabbits are an exception; their B cells develop in the appendix-sacculus rotundus. After reaching the IgM+ immature stage in the bone marrow, these immature B cells migrate to the spleen, where they are called transitional B cells, and some of these cells differentiate into mature B lymphocytes.

B cell development occurs through several stages, each stage representing a change in the genome content at the antibody loci. An antibody is composed of two identical light (L) and two identical heavy (H) chains, and the genes specifying them are found in the 'V' (Variable) region and the 'C' (Constant) region. In the heavy-chain 'V' region there are three segments; V, D and J, which recombine randomly, in a process called VDJ recombination, to produce a unique variable domain in the immunoglobulin of each individual B cell. Similar rearrangements occur for light-chain 'V' region except there are only two segments involved; V and J. The list below describes the process of immunoglobulin formation at the different stages of B cell development.

When the B cell fails in any step of the maturation process, it will die by a mechanism called apoptosis, here called clonal deletion.[4] If it recognizes self-antigen during the maturation process, the B cell will become suppressed (known as anergy) or undergo apoptosis (also termed negative selection). B cells are continuously produced in the bone marrow. When B cell receptors on the surface of the cell matches the detected antigens present in the body, the B cell proliferates and secretes a free form of those receptors (antibodies) with identical binding sites as the ones on the original cell surface. After activation, the cell proliferates and B memory cells would form to recognise the same antigen. This information would then be used as a part of the adaptive immune system for a more efficient and more powerful immune response for future encounters with that antigen.

B cell membrane receptors evolve and change throughout the B cell life span. TACI, BCMA and BAFF-R are present on both immature B cells and mature B cells. All of these 3 receptors may be inhibited by Belimumab. CD20 is expressed on all stages of B cell development except the first and last; it is present from pre-pre B cells through memory cells, but not on either pro-B cells or plasma ...