Introduction 3 monocyte (Mφ) subsets exist: CD14^hi/CD16^-, CD14^hi/CD16⁺and CD14^lo/CD16⁺. Reduced CD14^hiMφ surface expression of HLA-DR and failure to secrete pro-inflammatory cytokines in response to lipopolysaccharide (LPS) are thought to contribute to high infection rates and increased morbidity and mortality in Acute Liver Failure (ALF). We wanted to define CD14^hi. We investigated CD14^hiMφ phenotype and function and related gene expression profiles in hyperacute ALF (hALF).

Method Admission blood samples were obtained from 45 patients with hALF and from 19 healthy controls (HC). Mφ were phenotyped by flow cytometry (FCM) using fluorochrome-labelled antibodies to CD14, CD16, HLA-DR, HLA-DQ, CD86, CD80, CD40, CD163 and TLR4. Peripheral blood mononuclear cells (PBMCs) (10 HC, 11 hALF) were stimulated with LPS. Mφ intracellular TNFα, IL6 and IL10 were measured by FCM. CD14^hi/CD16^-and CD14^hi/CD16⁺Mφ from 4 patients with paracetamol-hALF and 3 HC were sorted by FCM and the extracted RNA used for transcriptome analysis (Affymetrix ST1 GeneChip®). We used Qlucore omics explorer package for initial gene identification and MetaCore^TMfor molecular pathway analysis.

Results A higher% of CD14^hi/CD16⁺and lower% of CD14^lo/CD16⁺Mφ were seen in hALF compared to HC (6.7% vs 4% and 1.2% vs 6.1%, p < 0.01). Both CD14^hiMφ subsets expressed lower surface levels of HLA-DR, HLA-DQ and CD86 (p < 0.001) but CD40 was unchanged and CD80 higher in hALF compared to HC (p < 0.001). Mφ TLR4 expression was similar in hALF and HC. Although CD14^hi/CD16^-Mφ CD163 was similar, CD14^hi/CD16⁺CD163 was higher in hALF than in HC (p < 0.001). CD14^hi/CD16⁺Mφ in patients who died or required transplantation had lower CD86 and higher CD163 than those who survived with medical management alone (p < 0.05). In response to LPS the 2 CD14^hisubsets were the predominant producers of cytokines. Compared to HC, only intracellular TNFα was lower in hALF CD14^hiMφ (p < 0.01) whilst IL6 tended to be so (p < 0.1) with no differences in IL10. TNFα production in CD14^hiMφ correlated with HLA-DR, HLA-DQ, CD86 and TLR4 expression (p < 0.01). Enrichment networks statistics identified reduced gene expression for MHC II processing (CIITA, HLA-DM, HLA-DP, HLA-DQ) and non-canonical NFκB signalling (NIK, NFκB2).

Conclusion Circulating CD14^hiMφ in hALF display phenotypic and functional similarities with anti-inflammatory, resolution-like macrophages that may be due to down-regulated non-canonical NFκB pathways. These 'pre-primed' Mφ may be beneficial in the resolution of liver injury in hALF but leave the patient dangerously susceptible to further infections.

Disclosure of interest None Declared.