B cell activation occurs in the secondary lymphoid organs (SLOs), such as the spleen and lymph nodes. After B cells mature in the bone marrow, they migrate through the blood to SLOs, which receive a constant supply of antigen through circulating lymph. At the SLO, B cell activation begins when the B cell binds to an antigen via its BCR. Although the events taking place immediately after activation have yet to be completely determined, it is believed that B cells are activated in accordance with the kinetic segregation model , initially determined in T lymphocytes. This model denotes that before antigen stimulation, receptors diffuse through the membrane coming into contact with Lck and CD45 in equal frequency, rendering a net equilibrium of phosphorylation and non-phosphorylation. It is only when the cell comes in contact with an antigen presenting cell that the larger CD45 is displaced due to the close distance between the two membranes. This allows for net phosphorylation of the BCR and the initiation of the signal transduction pathway . Of the three B cell subsets, FO B cells preferentially undergo T cell-dependent activation while MZ B cells and B1 B cells preferentially undergo T cell-independent activation.
B cells, unlike the other two classes of lymphocytes, T cells and natural killer cells , express B cell receptors (BCRs) on their cell membrane .  BCRs allow the B cell to bind to a specific antigen , against which it will initiate an antibody response. 
B cell , One of the two types of lymphocytes (the others being T cells ). All lymphocytes begin their development in the bone marrow . B cells are involved in so-called humoral immunity ; on encountering a foreign substance ( antigen ), the B lymphocyte differentiates into a plasma cell , which secretes immunoglobulin ( see antibody ).