Plasma cell S1P1 expression determines secondary lymphoid organ retention versus bone marrow tropism

Transcriptome analysis in primary B lymphoid precursors following induction of the pre-B cell receptor

Pre-BCR signals are part of a checkpoint where early precursor (pre-) B cells with a pairing Ig muH chain (muHC) are clonally expanded before they differentiate into IgL-rearranging, resting pre-B cells. A pre-BCR consists of two muHCs, two surrogate L chains and the signal transducer Igalpha/Igbeta. The molecular circuits by which the pre-BCR controls proliferation and differentiation of pre-B cells are poorly characterized. Therefore, we identified the differential transcriptome by genome-wide expression profiling in progenitor (pro-) B cells from a Rag2-deficient mouse, in which the expression of a transgenic muHC and thus a pre-BCR as well as pre-BCR-mediated clonal expansion can be controlled by tetracycline (muHC-inducible mouse). This analysis revealed that pre-BCR signals upregulate components of the BCR signalosome, open the IgL chain (LC) locus and induce the krüppel-like transcription factor KLF2, a key regulator of quiescence and lymphocyte migration. Hence, pre-BCR signals establish the molecular network for BCR signaling even before the production of an IgLC and induce the expression of KLF2, a candidate for controlling clonal expansion and migration of functional pre-B cells.

CXCR4 engagement promotes dendritic cell survival and maturation

It has been reported that human monocyte derived-dendritic cells (DCs) express CXCR4, responsible for chemotaxis to CXCL12. However, it remains unknown whether CXCR4 is involved in other functions of DCs. Initially, we found that CXCR4 was expressed on bone marrow-derived DCs (BMDCs). The addition of specific CXCR4 antagonist, 4-F-Benzoyl-TN14003, to the culture of mouse BMDCs decreased their number, especially the mature subset of them. The similar effect was found on the number of Langerhans cells (LCs) but not keratinocytes among epidermal cell suspensions. Since LCs are incapable of proliferating in vitro, these results indicate that CXCR4 engagement is important for not only maturation but also survival of DCs. Consistently, the dinitrobenzene sulfonic acid-induced, antigen-specific in vitro proliferation of previously sensitized lymph node cells was enhanced by CXCL12, and suppressed by CXCR4 antagonist. These findings suggest that CXCL12-CXCR4 engagement enhances DC maturation and survival to initiate acquired immune response.

11th annual Inflammatory and Immune Diseases Drug Discovery and Development Summit 12-13 March 2007, San Francisco, USA

The Strategic Research Institute (SRi) hosted the 11th International Inflammation and Immune Diseases Drug Discovery and Development World Summit in San Francisco during 12-13 March 2007. The summit comprised keynote sessions and two parallel tracks and focussed on targeting mechanisms for drug discovery and development, which modulate the immune response and which have anti-inflammatory activity in a number of human diseases. Indications included psoriasis, hepatitis C, allergic dermatitis, systemic lupus erythematosus, rheumatoid arthritis and osteoarthritis, multiple sclnerosis, cardiovascular disease and asthma. Data were presented supporting all stages of drug discovery from target identification and validation through to lead identification and optimisation to both early- and late-stage clinical development.

Sphingosine 1-phosphate receptors in health and disease: mechanistic insights from gene deletion studies and reverse pharmacology

Sphingosine 1-phosphate (S1P) is a bioactive sphingolipid that is critically involved in the embryonic development of the cardiovascular and central nervous systems. In the adult, S1P can produce cytoskeletal re-arrangements in many cell types to regulate immune cell trafficking, vascular homeostasis and cell communication in the central nervous system. S1P is contained in body fluids and tissues at different concentrations, and excessive production of the pleiotropic mediator at inflammatory sites may participate in various pathological conditions. Gene deletion studies and reverse pharmacology (techniques aiming to identify both ligands and function of receptors) provided evidence that many effects of S1P are mediated via five G-protein-coupled S1P receptor subtypes, and novel therapeutic strategies based on interaction with these receptors are being initiated. The prototype S1P receptor modulator, FTY720 (fingolimod), targets four of the five S1P receptor subtypes and may act at several levels to modulate lymphocyte trafficking via lymphocytic and endothelial S1P1 and, perhaps, other inflammatory processes through additional S1P receptor subtypes. A recently completed Phase II clinical trial suggested that the drug may provide an effective treatment of relapsing-remitting multiple sclerosis. FTY720 is currently being evaluated in larger-scale, longer-term, Phase III studies. This review provides an overview on S1P activities and S1P receptor function in health and disease, and summarizes the clinical experience with FTY720 in transplantation and multiple sclerosis.

Terminal differentiation of lymphocytes depends on Blimp-1

B lymphocyte induced maturation protein 1 (Blimp-1) has long been considered a master regulator of the terminal differentiation of B cells into antibody-secreting plasma cells. Gene-targeting experiments have now demonstrated that quantitative changes in Blimp-1 expression define plasma cell ontogeny--a process that requires the continual function of Blimp-1. Recently, new roles for Blimp-1 have been revealed, as a suppressor of diffuse large B cell lymphoma and as a key regulator of T-cell differentiation. Blimp-1 is expressed in differentiated effector T cells and controls their homeostasis. These new findings suggest that Blimp-1 has a conserved function in the final differentiation of both the cellular and the humoral arm of the adaptive immune response.

Sphingosine 1-phosphate regulates peritoneal B-cell trafficking for subsequent intestinal IgA production

Sphingosine 1-phosphate (S1P) is known to play a pivotal role in the regulation of lymphocyte emigration from organized lymphoid tissues such as the peripheral lymph nodes and thymus, but its immunologic role in unorganized and diffused tissues remains to be elucidated. Here we show that the trafficking of peritoneal B cells is principally regulated by S1P. All peritoneal B cells including B1a, B1b, and B2 B cells express comparable levels of the type 1 S1P receptor. Thus, treatment with FTY720, an S1P receptor modulator, caused the rapid disappearance of peritoneal B cells by inhibiting both their emigration from parathymic lymph nodes and their recirculation from the blood into the peritoneal cavity without affecting their progenitor populations. These changes did not affect natural plasma antibody production or phosphorylcholine (PC)–specific antibody production in serum after peritoneal immunization with heat-killed Streptococcal pneumoniae (R36A). However, FTY720 dramatically reduced peritoneal B cell-derived natural intestinal secretory IgA production without affecting the expression of J-chain and polyimmunoglobulin receptors. Additionally, FTY720 impaired the generation of PC-specific fecal IgA responses after oral immunization with R36A. These findings point to a pivotal role for S1P in connecting peritoneal B cells with intestinal B-cell immunity.