In A and B, each data point represents the average of 5 follicles from an individual mouse. To confirm that the translocation of MZ B cells in MFG-E8-/- mice Flupirtine maleate is caused by the accumulation of apoptotic cells, we injected 3 month old w.t. had enlarged MZ B cell compartments as well as an enhanced antibody response to NP-Ficoll. Moreover, a significant percentage of MZ B cells in aged MFG-E8-/- B6 mice migrated into follicles. Injecting apoptotic cells or oxidized LDL into wild type mice as well as physiological accumulation of LDL in ApoE-/- mice recapitulated the translocation of MZ B cells. To determine how MFG-E8 deficiency affects the functions of autoreactive B cells specific for nucleic acids in the periphery under non-inflammatory conditions, we utilized BCR transgenic mice Flupirtine maleate to bypass central selection and compared the differentiation of TLR9 dependent anti-dsDNA 56R B cells and TLR7 dependent anti-ssRNA H564 B cells in MFG-E8-/- mice. In MFG-E8-/- 56R mice, anti-dsDNA specific 56R/V38c B cells differentiated into MZ B cells but not AFCs. On the contrary, in MFG-E8-/-H564 mice, anti-ssRNA specific H564 B cells further differentiated into GC B cells and AFCs. Adoptive transfer of activated autoreactive B cells confirmed that Flupirtine maleate H564 B cells were more sensitive to apoptotic cell antigens than 56R B cells. Our observations provide new insights about the MZ B cell translocation in lupus patients as well as the dichotomy of TLR9 and TLR7 signals in the pathogenesis of lupus. Introduction Both central and peripheral tolerance play critical roles in controlling autoreactive B cells [1]. Most antibodies encoded by the germline are autoreactive. In bone marrow, autoreactive immature B cells are either deleted, forced to undergo receptor editing, or become anergic. Once they arrive in the periphery, mature B cells can re-acquire auto-reactivity through somatic mutation during GC (germinal center) reaction. Antigens deposited on FDCs (follicular dendritic cells) in the GC play an important role in selecting mutated B cells: B cells with the highest affinities differentiate into memory cells, whereas those with low affinities, including potentially autoreactive clones are deleted. The selection of autoreactive B cells depends on the threshold of B cell activation. Numerous animal Flupirtine maleate models have demonstrated that defects in both central and peripheral B cell tolerance are required to develop overt lupus-like disease[2]. Spleen B cells consist of two major populations: MZ (marginal zone) B cells and FO (follicular) B cells. Under normal conditions, MZ B cells and FO B cells are separated Flupirtine maleate by the marginal zone, which also includes various types of macrophages. Because of their location, marginal zone macrophages and B cells are the first line to capture and to respond to circulating antigens. An intact marginal zone is required to maintain an effective defense against both foreign and self antigens. Consistent with their innate-like immunity, the antibody repertoire of marginal zone B cells is enriched in poly-reactivity[3C5]. Moreover, marginal B cells also shuttle between the marginal zone and follicles to deposit antigens on FDCs[6]. Disrupting this shuttling through a S1P1 antagonist prevented optimal antibody responses [6]. In lupus patients, autoreactive 9G4+ B cells migrated into follicles [7], suggesting MZ B cells in lupus patients may be more facile in transporting auto-antigens and they may also directly participate in GC reactions. The signals that drive MZ B cell translocation in lupus patients have not been identified. In the well-established HEL model system, how antigens are presented determines the fate of HEL specific B cells [8]. Recent studies suggest similar mechanisms may Rabbit polyclonal to PITRM1 also apply to bona fide self-reactive B cells. Self antigens are associated with apoptotic cells. The lipid components of apoptotic cell membranes are oxidized [9]. These oxidized lipids, to some degree similar to the lipid found on surface of bacteria, provide neo-antigens to stimulate innate B cell responses [10]. Moreover, apoptotic blebs on the surface of apoptotic cells contain both DNA and RNA fragments [11, 12]. The elegant study by Leadbetter et al. demonstrated, these DNA and RNA fragments could form immune complexes with autoantibodies to provide endogenous TLR9 and TLR7 ligands thereby activating AM14 B cells [13]. However, because AM14 B cells are specific to IgG2a rather than self-antigen, how bona fide autoreactive B cells respond to apoptotic cells remains to be determined. Numerous mouse studies also demonstrated the dichotomy of TLR9 and TLR7 in lupus pathogenesis. While genetic deletion of TLR9 reduced the production anti-dsDNA, it exacerbated disease. On the contrary, deletion of TLR7 inhibited the production of anti-ssRNA antibody and prevented lupus [14]. These contrasting effects between TLR9 and TLR7 signals may reflect the different pathogenic potentials between anti-dsDNA and anti-ssRNA antibodies or different B cell responses to apoptotic cell associated nucleic acid antigens. Not only do apoptotic cells provide antigens to stimulate self-reactive B cells [11], they also accumulate in.
