Functional and transcriptomic changes in synergy of endotoxin and (1->3)-β-D-glucan in bone marrow derived macrophage from Fc gamma receptor IIb deficient mice 

Systemic lupus erythematosus (SLE) is an autoimmune disease with a diverse array of clinical symptoms. There are many factors including environmental factors may trigger disease progression. In this study, we investigated the influence of spontaneous gut leakage upon polymicrobial sepsis in Fc gamma receptor IIb deficient (FcgRIIb-/-) mice aged 8 and 40 weeks, as representing asymptomatic and symptomatic lupus, respectively. The spontaneous gut leakage as determined by i) the level of serum FITC-dextran, ii) increased serum endotoxin (LPS), and iii) increased serum (1->3)-b-D-glucan (BG), were demonstrated in symptomatic FcgRIIb-/- mice, but not in asymptomatic group. Moreover, spontaneous gut leakage was detected by increased serum BG without fungal infection was also found in SLE patients with lupus nephritis. Gut leakage induced by dextran sulfate solution (DSS) or LPS injection with BG or LPS alone, but not BG alone, enhanced the severity of cecal ligation and puncture (CLP) sepsis more prominently in 8-week-old FcgRIIb-/- mice. In addition, BG+LPS activated FcgRIIb-/- macrophages produced higher level of proinflammatory cytokine when compared with wild type macrophage. Moreover, BG+LPS activated macrophages enhanced expression of activating FcgRs, NF-kB and Syk compared with wild type macrophage. The inhibitor against Dectin-1, Syk and NF-kB, but not Raf-1, reduced supernatant TNF-α in BG+LPS activated macrophages implying Syk dependent signaling. Additionally, Syk abundance in FcgRIIb-/- mice and in CLP surgery were higher than wild type mice possibly due to several Syk-activator (anti-dsDNA, LPS and BG), and Syk inhibitor attenuated proteinuria and serum cytokine only in FcgRIIb-/- mice. Moreover, administration of a Syk inhibitor prior CLP surgery in FcgRIIb-/- mice attenuated sepsis severity as evaluated by mortality, organ injury, Serum LPS and post serum cytokines. Furthermore, RNA sequencing analysis of BG+LPS activated macrophages with or without Syk inhibitor treatment, we found that Syk inhibitor downregulated several inflammatory pathways in macropahges, suggesting the potential anti-inflamatory impact of Syk inhibitor in lupus. The genes that found in BG+LPS activated macrophages associated with the prediction of genes involve in mortality in sepsis patients and Syk inhibitor treatment reversed almost direction of those genes.             In conclusion, spontaneous gut leakage and the induction of gut permeability worsened sepsis severity. Gut translocation of LPS and BG showed minor effect on wild type mice, but the synergistic effect of BG and LPS was prominent in FcgRIIb-/- mice, suggesting the therapeutic strategies addressing gut leakage may be interest in sepsis condition in patient with sepsis. In addition, Syk signaling is promising therapeutic target for SLE patients. Syk inhibitor appears to be an alternative drug for treatment of lupus with a counter on sepsis.