Background/Purpose: Macrophage activation syndrome (MAS), a form of secondary hemophagocytic lymphohistiocytosis (HLH), is a potentially fatal complication of rheumatic diseases. MAS is a dysfunctional hyperinflammatory response characterized by abnormal activation of lymphocytes and phagocytes, leading to an overproduction of inflammatory cytokines and damage to host tissues. Circulating monocytes are highly responsive to their surrounding environment, are known to exhibit phenotypic and functional changes during inflammation, and can give rise of macrophages that phagocytose immune cells. However, monocytes and macrophages have not been well-studied in MAS. MAS is most commonly associated with systemic juvenile idiopathic arthritis (sJIA). At least 10% of sJIA patients will experience an overt episode of MAS with up to 50% exhibiting signs of subclinical inflammation.

Methods: We analyzed classical CD14+ monocytes from children with active MAS (6 subjects) compared to individuals with sJIA without MAS (4 subjects) and age/sex/race matched healthy children (8 subjects) by flow cytometry and RNA sequencing (RNA-Seq). Two MAS subjects and two age/sex/race matched healthy controls were analyzed by single cell RNA sequencing (scRNA-Seq). Subjects with MAS were defined based on the 2016 classification criteria by Ravelli and colleagues as well as the ratio of ferritin to ESR. Differentially expressed genes (DEGs) were defined as those with at least 2 fold change and false discovery rate less than 0.1.

Results: We found significant upregulation of CD16 surface expression during active MAS, which rapidly reversed after treatment with systemic steroids. Our RNA-Seq data show broad transcriptional changes in CD14+ monocytes from children with active MAS, including upregulation of RNase 2 (involved in processing RNAs for the innate immune sensor TLR8) and SLAMF7 (associated with monocyte/macrophage hyperinflammation in response to interferon gamma). scRNA-Seq analyses of myeloid cells from two subjects with active MAS revealed a strong interferon signature in MAS monocytes, including enrichment for STAT1, IRF1, IFITM3, ISG15, and GBPs, and upregulation of alarmins, including S100A8, S100A9, and S100A12. We identified hemoglobin transcripts specifically in the cells from MAS subjects by scRNA-Seq, suggesting the detection of hemophagocytes in circulation. We are currently analyzing myeloid cells of additional MAS subjects using scRNA-Seq.

Conclusion: These data confirm an important role for cytokines, specifically interferons, in driving gene expression in monocytes during MAS and suggest potential targets for future therapies. Together, our data show that CD14+ monocytes have a unique transcriptional signature in MAS and support a role for interferon signaling and enhanced RNA sensing in active disease.

ACR Meeting Abstracts - https://acrabstracts.org/abstract/transcriptional-analysis-of-cd14-monocytes-during-macrophage-activation-syndrome-highlights-role-for-interferons-and-rna-sensing-in-monocytes/