Unlike their precursors,<unk> s cannot switch antibody classes, cannot act as antigen-presenting cells because they no longer display MHC-II, and do not take up antigen because they no longer display significant quantities of immunoglobulin on the cell surface. However, continued exposure to antigen through those low levels of immunoglobulin is important, as it partly determines the cell's lifespan. The lifespan, class of antibodies produced, and the location that the<unk>  moves to also depends on signals, such as cytokines, received from the T cell during differentiation. Differentiation through a T cell-independent antigen stimulation (stimulation of a B cell that does not require the involvement of a T cell) can happen anywhere in the body and results in short-lived cells that secrete IgM antibodies. The T cell-dependent processes are subdivided into primary and secondary responses: a primary response (meaning that the T cell is present at the time of initial contact by the B cell with the antigen) produces short-lived cells that remain in the extramedullary regions of lymph nodes; a secondary response produces longer-lived cells that produce IgG and IgA, and frequently travel to the bone marrow. For example,<unk> s will likely secrete IgG3 antibodies if they matured in the presence of the cytokine interferon-gamma. Since B cell maturation also involves somatic hypermutation (a process completed before differentiation into a<unk> , these antibodies frequently have a very high affinity for their antigen.<unk> s can only produce a single kind of antibody in a single class of immunoglobulin. In other words, every B cell is specific to a single antigen, but each cell can produce several thousand matching antibodies per second. This prolific production of antibodies is an integral part of the humoral immune response. Long-lived<unk> s The current findings suggest that after the process of affinity maturation in germinal centers,<unk> s develop into one of two types of cells: short-lived<unk> s (SLPC) or long-lived<unk> s (LLPC). LLPC mainly resides in the bone marrow for a long period of time and secrete antibodies, thus providing long-term protection. LLPC can maintain antibody production for decades or even for a lifetime of an individual, and, unlike B cells, LLPC do not need antigen restimulation to generate antibodies. Human LLPC population can be identified as CD19–CD38hiCD138+ cells. The long-term survival of LLPC is dependent on a specific environment in the bone marrow, the<unk>  survival niche. Removal of LLPC from its survival niche results in its rapid death. Survival niche can only support limited number of LLPC, thus the niche’s environment must protect its LLPC cells but yet be able to adapt to new arrivals. The<unk>  survival niche is defined by combination of cellular and molecular factors and even though it is yet to be properly define, there have been several molecules identified that support the survival of LLPC, such as IL-5, IL-6, TNF-α, stromal cell-derived factor-1α, and signalling via CD44. LLPC can also be found, in lesser degree, in gut-associated lymphoid tissue (GALT), where they are producing IgA antibodies and contribute to mucosal immunity. Recent findings suggests that<unk> s in gut do not necessarily need to be generated de novo from active B cells but there are also long-lived<unk> , which suggest similar survival niche as in bone marrow. Tissue specific niches, that allow the survival of LLPC, have been also described in nasal-associated lymphoid tissues (NALT), human tonsillar lymphoid tissues and human mucosa or mucosa-associated lymphoid tissues (MALT). Originally it was thought that the continuous production of antibodies is a result of constant replenish of short-lived<unk> s by memory B cells re-stimulation. Recent findings, however, show that some<unk>  are truly long-lived. Studies have shown that the absence of antigen and the depletion of B cells did not have effect on the production of high-affinity antibodies by the LLPC. Prolong depletion of B cells (with anti-CD20 monoclonal antibody treatment that affects B cells but not<unk>  also did not affect antibody titres. LLPC secret high levels of IgG independently of B cells. LLPC in bone marrow are the main source of circulating IgG in humans. Even though IgA production is traditionally associated with mucosal sites, some<unk> s in bone marrow also produce IgA. We can also find LLPC in bone marrow producing IgM.
Plasma cell
Prolymphocyte
Monocyte
Reactive lymphocyte
Thymocyte
Podocyte
Dendritic cell
Koilocyte