PRCCs appear to be, in general, the most efficient and reliable among sampling-based indexes (45)

PRCCs appear to be, in general, the most efficient and reliable among sampling-based indexes (45). mathematical modeling. Labeling was much faster in depleted mice. Compared to MBQ-167 control mice, B cell-depleted mice exhibited a higher proliferation rate in the pro-/pre-B compartment, and higher cell death and lower differentiation in the immature B cell compartment. We validated the first result by analysis of the expression of Ki67, the nuclear protein expressed in proliferating cells, and the second using Annexin V staining. Collectively, our results suggest that B lymphopoiesis is subjected to homeostatic feedback mechanisms imposed by mature B cells in the peripheral compartment. Keywords: B lymphocytes, BrdU, computer simulation, homeostatic feedback, mathematical modeling Introduction B cell development starts in the bone marrow (BM) and continues in the spleen to final maturation. Developmental progression is guided by sequential events leading to assembly, expression, and signaling of the B cell antigen receptor (BCR). Heavy MBQ-167 (H) and light (L) chain immunoglobulin genes are rearranged at the pro-B and pre-B stages (respectively), and complete surface IgM is expressed at the immature stage (1C5). Further developmental progression and maturation in the periphery are limited by positive and negative selection, mediated by BCR signaling and aiming to construct a non-self-reactive, immune-competent repertoire of na?ve B cells (2, 6). In the adult mouse, the number of mature B cells remains constant, despite continuous production of new cells in the BM. It has been estimated that 1C2??107 immature B cells are generated daily in the adult mouse and leave the BM as transitional B cells (7), but only about 3% enter the pool of mature B cells (8). Another source of B cell input to the peripheral compartment is antigen-driven proliferation. Cell death due to several factors including self-reactivity (9), incomplete maturation (10), competition for follicular niches (11), and trophic mediators (12) limits the size of the peripheral compartment. Thus, the balance between cell production and cell death maintains the size of the peripheral B cell MBQ-167 compartment unchanged (13). To understand this homeostatic control, it is of critical importance to quantify the rate of B lymphopoiesis under physiological conditions. This question has been the subject of several investigations in the past, employing different approaches. Experiments based on an irradiation/autoreconstitution model of marrow-derived B cell differentiation demonstrated that frequencies of pro-/pre-B cells (14, 15) and immature B cells (16) increase after irradiation, and so does differentiation and maturation (17, 18). It has also been demonstrated that upon immunological challenge, BM B lymphopoiesis increases, as measured by cell number, cell division, and turnover (19, 20). These experiments supported the concept that B lymphopoiesis is regulated by a feedback mechanism imposed by peripheral B cells and/or environmental stimuli. Other experiments have used mixed BM chimeras to suggest that B cell production in the BM is not subjected to feedback inhibition by the peripheral B cell compartment but is rather autonomously regulated (21, 22). Similarly, in mice depleted of B cells from birth by anti-IgM antibodies, or in hematologically mutant mice (20), no difference was found in the proliferation rate of pre-B cells relative to controls. There are also contradicting results about the influence of serum immunoglobulins on the regulation of developing B cell populations in the Mouse monoclonal to TYRO3 BM (23, 24). Possible causes for the different conclusions may be attributed to the profound differences in the experimental systems used to eliminate the peripheral B cell compartment and to the complexity of both models in affecting other lineages and tissues. Moreover, quantification of B cell production in each of the above studies was based on a single measurement of cell frequency, which may be differentially affected in each experimental setup, rather than on a series of kinetic measurements. Thus, while the concept that B.