Abstract
IntroductionAn NZB-derived genetic locus (Sle2c2) that suppresses autoantibody production in a mouse model of induced systemic lupus erythematosus contains a polymorphism in the gene encoding the G-CSF receptor. This study was designed to test the hypothesis that the Sle2c2 suppression is associated with an impaired G-CSF receptor function that can be overcome by exogenous G-CSF.MethodsLeukocytes from B6.Sle2c2 and B6 congenic mice, which carry a different allele of the G-CSF receptor, were compared for their responses to G-CSF. Autoantibody production was induced with the chronic graft-versus-host-disease (cGVHD) model by adoptive transfer of B6.bm12 splenocytes. Different treatment regimens varying the amount and frequency of G-CSF (Neulasta®) or carrier control were tested on cGVHD outcomes. Autoantibody production, immune cell activation, and reactive oxygen species (ROS) production were compared between the two strains with the various treatments. In addition, the effect of G-CSF treatment was examined on the production autoantibodies in the B6.Sle1.Sle2.Sle3 (B6.TC) spontaneous model of lupus.ResultsB6.Sle2c2 and B6 leukocytes responded differently to G-CSF. G-CSF binding by B6.Sle2c2 leukocytes was reduced as compared to B6, which was associated with a reduced expansion in response to in vivo G-CSF treatment. G-CSF in vivo treatment also failed to mobilize bone-marrow B6.Sle2c2 neutrophils as it did for B6 neutrophils. In contrast, the expression of G-CSF responsive genes indicated a higher G-CSF receptor signaling in B6.Sle2c2 cells. G-CSF treatment restored the ability of B6.Sle2c2 mice to produce autoantibodies in a dose-dependent manner upon cGVHD induction, which correlated with restored CD4+ T cells activation, as well as dendritic cell and granulocyte expansion. Steady-state ROS production was higher in B6.Sle2c2 than in B6 mice. cGVHD induction resulted in a larger increase in ROS production in B6 than in B6.Sle2c2 mice, and this difference was eliminated with G-CSF treatment. Finally, a low dose G-CSF treatment accelerated the production of anti-dsDNA IgG in young B6.TC mice.ConclusionThe different in vivo and in vitro responses of B6.Sle2c2 leukocytes are consistent with the mutation in the G-CSFR having functional consequences. The elimination of Sle2c2 suppression of autoantibody production by exogenous G-CSF indicates that Sle2c2 corresponds to a loss of function of G-CSF receptor. This result was corroborated by the increased anti-dsDNA IgG production in G-CSF-treated B6.TC mice, which also carry the Sle2c2 locus. Overall, these results suggest that the G-CSF pathway regulates the production of autoantibodies in murine models of lupus.
Highlights
An NZB-derived genetic locus (Sle2c2) that suppresses autoantibody production in a mouse model of induced systemic lupus erythematosus contains a polymorphism in the gene encoding the granulocyte-colony stimulation factor (G-CSF) receptor
B6.Sle2c2 leukocytes bind less G-CSF and expand less to exogenous G-CSF than B6 To determine whether the S378N mutation in the extracellular domain of the granulocyte-colony stimulation factor receptor (G-CSFR)-affected ligand binding, we compared in vitro binding of mouse G-CSF (mG-CSF) between B6 and B6.Sle2c2 splenocytes
As in the blood of non-induced mice (Figure 1B), the 12 × 2 expanded the CD11b+ GR1lo population in B6.Sle2c2 mice three weeks after chronic graft vs host disease (cGVHD) induction and resulted in equivalent percentages in both strains (Figure 5B). These results showed that restoration of the cGVHD response in B6.Sle2c2 mice by human granulocyte-colony stimulation factor (huG-CSF) treatment correlated with an increase in CD4+ T cell activation, and an expansion of the dendritic cell (DC), neutrophils and CD11b+ GR1lo cell populations
Summary
An NZB-derived genetic locus (Sle2c2) that suppresses autoantibody production in a mouse model of induced systemic lupus erythematosus contains a polymorphism in the gene encoding the G-CSF receptor. The strong genetic basis of SLE is sustained by a large number of polymorphisms that have been identified in recent years through association studies in large cohorts of patients and controls [1]. Mouse models of SLE have been used extensively to study both the cellular and genetic basis of SLE, and overall, the results obtained from these models have largely been validated in SLE patients. Murine models have revealed a large number of SLE susceptibility genes, which are organized in the same three broad pathways: apoptosis and processing of apoptotic debris, toll-like receptor (TLR) signaling and type I IFN pathways, and lymphocyte activation in both SLE patients and SLE-prone mice [2,3]. The SLEresistant strain C57BL/6 (B6) carries susceptibility genes that were revealed when combined with either other susceptibility genes provided by the NZM2410 lupusprone genome, or when subjected to a strong immune stimulation [4,5]
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