Elsevier

Autoimmunity Reviews

Volume 6, Issue 3, January 2007, Pages 149-154
Autoimmunity Reviews

The mosaic of B-cell subsets (with special emphasis on primary Sjögren's syndrome)

https://doi.org/10.1016/j.autrev.2006.09.011Get rights and content

Abstract

Major breakthroughs have occurred with classification of B-cells into populations and subpopulations. With respect to their expression of CD5, they comprise the B1 and B2 populations, with the former further divided into B1a and B1b subpopulations. The oncologic process starts from transitional type 1 (T1) and T2 immature B-cells, through marginal zone or germinal center B-cells, ending up with memory B-cells and plasma cells (PCs). They may also be categorized based on their functional commitment with polarized B effector (Be)1 and Be2, with B-activating factor of the tumor-necrosis factor-producing B-cells, and with short-lived and long-lived PCs. Such a seemingly homogeneous family of cells has thus turned out to be a genuine mosaic of B-lymphocyte subsets.

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

  • CD5-associated protein-tyrosine phosphatase are involved in B-cell antigen receptor signaling.

  • Immature transitional B-cells migrate from primary lymphoid organs (the bone marrow) to secondary lymphoid organs (the spleen).

  • Marginal zone B-cells stand at the front line of the immune defenses.

  • T-cells, B-cells, and follicular dendritic cells gather together within conventional or ectopic germinal centers.

  • B-cells may be classified based on their functional commitment.

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