Using a flow cytometric approach we analysed the frequencies FK866 molecular weight as well as the absolute counts of naive, switched and non-switched memory B cells, CD27-negative memory B cells, transitional B cells as well as CD21lowCD38low B cells from neonates

up to the age of 50 years. Most of the B cell subsets showed age-dependent developmental changes: while the peripheral B cell pool during infancy is characterized predominantly by transitional and naive B cells, the fraction of switched and non-switched memory B cells increases gradually with age. CD21lowCD38low B cells as well as plasmablasts do not exhibit developmental changes. In summary, we could demonstrate particular changes in the peripheral blood B cell compartment during ontogeny. This study provides reference values of different B cell subpopulations offering comparability for studies addressing disturbed peripheral B cell development in immunodeficiency, autoimmunity or B cell reconstitution following cell-depleting therapies. As in all components of the immune system a balance EPZ-6438 in vitro between activation and regulation is important for an effective humoral defence, illustrated by a disturbed balance in autoimmune or immunodeficiency diseases [1,2]. B cell maturation and differentiation follows

distinct developmental stages and might be impaired by B cell intrinsic or extrinsic factors. The early steps of B cell development take place in the bone marrow, where B cell precursors develop into pro- and pre-B cells while rearranging their immunoglobulin light and heavy chain genes. B cell maturation and differentiation is proceeding further in secondary lymphoid organs [3]. The phenomenon of B cell memory is based upon the existence mafosfamide of bone marrow-residing long-lived plasma cells producing high-affinity antibodies as well as upon the continuous circulation of affinity-matured memory B cells, which might differentiate readily into effector cells upon cognate encounter of foreign antigen [4]. The impaired generation of B cell memory

is characteristic in several immunodeficiencies, whereas uncontrolled generation and activation of memory B cells or plasma cells might lead to autoimmune diseases. Both settings might be reflected in the composition of the peripheral B cell pool. Flow cytometric immunophenotyping has been used to delineate distinct stages of peripheral B cell maturation and differentiation in humans. Using CD38 and immunoglobulin (Ig)D as differentiation markers, B cells have been divided into different populations (Bm1–Bm5) according to their differentiation stage in the lymphoid organs [5]. Using CD27 as a surrogate marker of human memory B cells, together with the surface expression of IgD, B cells have been divided into four distinct populations [6,7]: whereas IgD+CD27- B cells represent the naive B cell pool, the expression of CD27 and loss of surface IgD expression on B cells is a feature of classical switched memory B cells.