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Objective. To investigate whether histone‐specific T helper (Th) cells that are able to induce anti‐doublestranded DNA (anti‐dsDNA) antibodies can be isolated from patients with systemic lupus erythematosus (SLE) and to characterize the cytokine secretion pattern of such Th clones. Methods. Peripheral blood mononuclear cells from SLE patients and healthy donors were stimulated with autologous apoptotic cell material or purified histones, expanded with interleukin‐2 (IL‐2), and cloned by limiting dilution. Histone reactivity of clones was examined by histone‐specific proliferation and cytokine release. Cytokines were determined by enzyme‐linked immunosorbent assay (ELISA) and CTLL‐2 bioassay. Induction of anti‐dsDNA antibodies was measured in cocultures of autologous B cells and Th clones by ELISA. Results. Numerous histone‐specific T cell receptor (TCR) α/β+ Th clones were established from 2 of 3 patients with active SLE and from 1 of 2 healthy individuals. Most Th clones secreted IL‐2, interferon‐γ (IFNγ), and IL‐4, whereas some produced predominantly IL‐2 and lFNγ. Th clones that could stimulate the production of anti‐dsDNA antibodies were derived from SLE patients and from a healthy individual. Conclusion. Th cells specific for histones may play an important role in the pathogenesis of SLE by inducing autoantibodies to dsDNA. Both Th1 and Th2 cytokines may be involved in the pathogenesis of SLE. The presence of histone‐specific Th cells in a healthy individual indicates the importance of peripheral tolerance for preventing autoimmunity to nuclear antigens.

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Cells navigating through complex tissues face a fundamental challenge: while multiple protrusions explore different paths, the cell needs to avoid entanglement. How a cell surveys and then corrects its own shape is poorly understood. Here, we demonstrate that spatially distinct microtubule dynamics regulate amoeboid cell migration by locally promoting the retraction of protrusions. In migrating dendritic cells, local microtubule depolymerization within protrusions remote from the microtubule organizing center triggers actomyosin contractility controlled by RhoA and its exchange factor Lfc. Depletion of Lfc leads to aberrant myosin localization, thereby causing two effects that rate-limit locomotion: (1) impaired cell edge coordination during path finding and (2) defective adhesion resolution. Compromised shape control is particularly hindering in geometrically complex microenvironments, where it leads to entanglement and ultimately fragmentation of the cell body. We thus demonstrate that microtubules can act as a proprioceptive device: they sense cell shape and control actomyosin retraction to sustain cellular coherence.

Vav-1 and Vav-2 are closely related Dbl-homology GTP exchange factors (GEFs) for Rho GTPases. Mutation of Vav-1 disrupts T cell development and T cell antigen receptor-induced activation, but has comparatively little effect on B cells. We found that combined deletion of both Vav-1 and Vav-2 in mice resulted in a marked reduction in mature B lymphocyte numbers. Vav-1(-/-)Vav-2(-/-) B cells were unresponsive to B cell antigen receptor (BCR)-driven proliferation in vitro and to thymus-independent antigen in vivo. BCR-stimulated intracellular calcium mobilization was greatly impaired in Vav-1(-/-)Vav-2(-/-) B cells. These findings establish a role for Vav-2 in BCR calcium signaling and reveal that the Vav family of GEFs is critical to B cell development and function.

Objective. Uningested dead cells may be an important source of autoantigens and may trigger autoimmune diseases such as systemic lupus erythematosus (SLE). Multiple receptors involved in the clearance of apoptotic cells have been described; however, little is known about the receptors and ligands involved in uptake of necrotic cells that release autoantigens as well.Methods. The uptake of autologous necrotic peripheral blood lymphocytes into human monocyte-derived macrophages was qualitatively and quantitatively monitored by confocal microscopy and 2-color flow cytometry, respectively. Blocking experiments were performed to examine the receptors and molecules involved in the phagocytosis of necrotic cells. Cytokine secretion by lipopolysaccharide-activated monocytes and macrophages was determined by enzyme-linked immunosorbent assay.

Lsc (the murine homolog of human p115 Rho GEF) is a member of the Dbl-homology family of GTP exchange factors and is a specific activator of Rho. Lsc is activated by the G alpha(13) subunit of heterotrimeric G proteins and contains a regulator of G protein signaling domain that downmodulates G alpha(12) and G alpha(13). Lsc is expressed primarily in the hematopoietic system and links the activation of G alpha(12) and G alpha(13)-coupled receptors to actin polymerization in B and T cells. Lsc is essential for marginal zone B (MZB) cell homeostasis and for the generation of immune responses. Although Lsc-deficient lymphocytes show reduced basal motility, MZB cells show enhanced migration after serum activation. Thus, Lsc is a critical regulator of MZB cells and immune functions.

Marginal zones (MZs) are microdomains in the spleen that contain various types of immune cells, including MZ B cells, MOMA1 ϩ metallophilic macrophages, and mucosal addressin cell adhesion molecule 1 (MAdCAM-1) ϩ endothelial cells. MAdCAM-1 ϩ and MOMA1 ϩ cells line the sinus, that separates MZs from splenic follicles. Here we show that a receptor for the lysophospholipid sphingosine-1-phosphate (S1P), S1P 3 , is required for normal numbers of splenic immature and MZ B cells, and for S1P-induced chemotaxis of MZ B cells. S1P 3 is also essential for proper alignment of MOMA1 ϩ macrophages and MAdCAM-1 ϩ endothelial cells along the marginal sinus. The lack of cohesion of the marginal sinus in S1P 3 Ϫ / Ϫ mice affects MZ B cell functions, as wild-type (WT) MZ B cells migrate more into S1P 3 Ϫ / Ϫ follicles than into WT follicles after treatment with lipopolysaccharide. Additionally, short-term homing experiments demonstrate that WT MZ B cells home to the S1P 3 Ϫ / Ϫ spleen in increased numbers, suggesting a role for the marginal sinus in regulating MZ B cells numbers. Moreover, S1P 3 Ϫ / Ϫ mice are defective in mounting immune responses to thymus-independent antigen type 2 due to defects in radiation-resistant cells in the spleen. These data identify lysophospholipids and the S1P 3 receptor as essential regulators of the MZ sinus and its role as a barrier to the follicle.