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B cell
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<p>B cells, also known as B lymphocytes, are a type of [lymphocyte]]. They function in the <a href="/facts/Humoral_immunity/qG9I4pGf">humoral immunity</a> component of the <a href="/facts/Adaptive_immune_system/bc7zT1Jo">adaptive immune system</a>. B cells produce <a href="/facts/Antibody/MX8pdTdP">antibody</a> molecules which may be either secreted or inserted into the plasma membrane where they serve as a part of <a href="/facts/B-cell_receptor/J6qRYYkN">B-cell receptors</a>. When a naïve or <a href="/facts/Memory_B_cell/3Qaz8Pxd">memory B cell</a> is activated by an antigen, it proliferates and differentiates into an antibody-secreting effector cell, known as a plasmablast or plasma cell. In addition, B cells <a href="/facts/Antigen_presentation/RMEAcYwR">present antigens</a> (they are also classified as professional <a href="/facts/Antigen-presenting_cell/No0wr2uU">antigen-presenting cells, APCs</a>) and secrete <a href="/facts/Cytokine/SdWpWABH">cytokines</a>. In <a href="/facts/Mammal/phSwTzBo">mammals</a> B cells <a href="/facts/Cellular_differentiation/bCVqUG7w">mature</a> in the <a href="/facts/Bone_marrow/4dfudk0H">bone marrow</a>, which is at the core of most <a href="/facts/Bone/pCU37jBe">bones</a>. In <a href="/facts/Bird/RJF6zwLP">birds</a>, B cells mature in the <a href="/facts/Bursa_of_Fabricius/L5agpxs2">bursa of Fabricius</a>, a lymphoid organ where they were first discovered by Chang and Glick, which is why the <i>B</i> stands for <i>bursa</i> and not <i>bone marrow</i>, as commonly believed. </p><p>B cells, unlike the other two classes of lymphocytes, <a href="/facts/T_cell/5z6PQ9UN">T cells</a> and <a href="/facts/Natural_killer_cell/A3THWxrJ">natural killer cells</a>, express <a href="/facts/B-cell_receptor/J6qRYYkN">B cell receptors (BCRs)</a> on their <a href="/facts/Cell_membrane/vAXSD0DT">cell membrane</a>. BCRs allow the B cell to <a href="/facts/Molecular_binding/cBnorUC5">bind</a> to a foreign <a href="/facts/Antigen/9JlAernG">antigen</a>, against which it will initiate an antibody response. B cell receptors are extremely specific, with all BCRs on a B cell recognizing the same <a href="/facts/Epitope/PL0oBuGh">epitope</a>. </p>