The mosaic of B-cell subsets (with special emphasis on primary Sjögren's syndrome)
Section snippets
Subsets of B-cells
It is now well over 20 years since the T-cell marker CD5 was discovered on leukemic B-cells [5], and seen on a minority of normal B-cells. They comprise two populations: B1 lymphocytes that encompass the intriguing CD5+B-cell population, and B2 lymphocytes that represent the regular CD5−B-cell population [6]. Advances in leukocyte phenotyping have divided the B1 population into two subpopulations [7]: B1a lymphocytes that express CD5, and B1b lymphocytes that do not, but share all the other
Transitional B-cells
After birth, B-cells originate in the bone marrow (BM). As soon as they have productively rearranged their immunoglobulin (Ig) genes, pro-B-cells proceed to the pre-B-cell stage. Then, as transitional B-cells, they are pushed into migrating from the BM to secondary lymphoid organs. There, they carry on maturing, and are further-selected by Ags.
Transitional B-cells have long been described in rodents [18], but only recently identified in humans [19]. As type 1, they present as CD20+ CD5+ CD10+/−
Polarized B-cells
There exist two distinct effector T-helper (Th) compartments, referred to as Th1 and Th2. This cliché has been substantiated over the years. Effector cells produce distinct spectra of cytokines compatible with the kind of response adjusted to particular Ags. Thus, Th1 cells secrete, among other cytokines, interferon (IFN)-γ and interleukin (IL)-2 whereas Th2 cells produce, among others, IL-4, IL-5 and IL-6. The latter set favors activation and maturation of B-lymphocytes. In turn, Th1 cytokines
Take-home messages
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CD5-associated protein-tyrosine phosphatase are involved in B-cell antigen receptor signaling.
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Immature transitional B-cells migrate from primary lymphoid organs (the bone marrow) to secondary lymphoid organs (the spleen).
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Marginal zone B-cells stand at the front line of the immune defenses.
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T-cells, B-cells, and follicular dendritic cells gather together within conventional or ectopic germinal centers.
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B-cells may be classified based on their functional commitment.
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