B cells drive lymphocyte activation and expansion in mice with the CD45 wedge mutation and Fas deficiency.

CD45 and Fas regulate tyrosine phosphorylation and apoptotic signaling pathways, respectively. Mutation of an inhibitory wedge motif in CD45 (E613R) results in hyperresponsive thymocytes and B cells on the C57BL/6 background, but no overt autoimmunity, whereas Fas deletion results in a mild autoimmune disease on the same genetic background. In this study, we show that these two mutations cooperate in mice, causing early lethality, autoantibody production, and substantial lymphoproliferation. In double-mutant mice, this phenotype was dependent on both T and B cells. T cell activation required signaling in response to endogenous or commensal antigens, demonstrated by the introduction of a transgenic T cell receptor. Genetic deletion of B cells also prevented T cell activation. Similarly, T cells were necessary for B cell autoantibody production. However, B cells appeared to be intrinsically activated even in the absence of T cells, suggesting that they may drive the phenotype of these mice. These results reveal a requirement for careful control of B cell signaling and cell death in preventing inappropriate lymphocyte activation and autoimmunity.

An orally bioavailable spleen tyrosine kinase inhibitor delays disease progression and prolongs survival in murine lupus.

OBJECTIVE: To assess whether R788, an orally bioavailable small molecule inhibitor of spleen tyrosine kinase (Syk)-dependent signaling, could modulate disease in lupus-prone (NZB x NZW)F1 (NZB/NZW) mice via inhibition of Fc receptor (FcR) and B cell receptor signaling. METHODS: R788 was administered to NZB/NZW mice before and after disease onset. Proteinuria, blood urea nitrogen levels, and autoantibody titers were examined periodically, and overall survival and renal pathologic features were assessed following long-term treatment (24-34 weeks). The distribution and immunophenotype of various splenic T cell and B cell subpopulations were evaluated at the time of study termination. Arthus responses in NZB/NZW mice pretreated with R788 or Fc-blocking antibody (anti-CD16/32) were also examined. RESULTS: When R788 was administered prior to or after disease onset, it delayed the onset of proteinuria and azotemia, reduced renal pathology and kidney infiltrates, and significantly prolonged survival of lupus-prone NZB/NZW mice; autoantibody titers were minimally affected throughout the study. Dose-dependent reductions in the numbers of CD4+ activated T cells expressing high levels of CD44 or CD69 were apparent in spleens from R788-treated mice. Minimal effects on the numbers of naive T cells expressing CD62 ligand and total CD8+ T cells per spleen were observed following long-term drug treatment. R788 pretreatment resulted in reduced Arthus responses in NZB/NZW mice, similar to results obtained in mice pretreated with FcR-blocking antibody. CONCLUSION: We demonstrate that a novel Syk-selective inhibitor prevents the development of renal disease and treats established murine lupus nephritis. These data suggest that Syk inhibitors may be of therapeutic benefit in human lupus and related disorders.

Prevention of renal damage in murine lupus nephritis by CTLA-4Ig and cyclophosphamide.

OBJECTIVE: To compare the effects of combined administration of cyclophosphamide (CYC) and CTLA-4Ig with the effects of these agents alone on the immunopathology and progression of renal damage in (NZB x NZW)F(1) (B/W) lupus-prone mice, and to explore the clinical implications of this combination by evaluating the ability of CTLA-4Ig to sustain the benefit of CYC in patients with lupus nephritis. METHODS: We carried out a detailed, prospective pathologic and immunohistochemical analysis of the effects of CYC and CTLA-4Ig, alone and in combination, in kidney tissue from B/W mice. The acute effects of these agents on immune cells in the kidney were evaluated by fluorescence-activated cell sorting. We also compared the effect of brief CYC plus sustained CTLA-4Ig administration with the effect of sustained administration of both agents on the progression of renal disease in B/W mice. RESULTS: As a single agent, CTLA-4Ig was generally as effective, and in some cases more effective, than CYC in slowing progression of renal disease. Combined therapy with these two agents very effectively arrested the progression of renal damage and, in some respects, reversed renal pathology. Induction therapy with both CTLA-4Ig and CYC precluded the need for continuous administration of CYC. CONCLUSION: Our results indicate that the combination of CTLA-4Ig and CYC very effectively arrests the progression of murine lupus nephritis. These findings have direct implications for the treatment of lupus nephritis.