Background: Sarcoidosis (SAR) is a systemic inflammatory disease characterized by the presence of granulomas. SAR shares many similarities with tuberculosis (TB). The mechanisms underlying the granulomatous reaction in SAR are not fully understood; its formation is the result of the activation and recruitment of circulating immune cells, including monocytes. Monocytes have a memory capacity, known as trained immunity, which is based on epigenetic and metabolic changes.

Objectives: Our objective is to investigate the role of trained immunity in the pathophysiology of SARS, as evidenced by a monocyte epigenetic signature.

Methods: We conducted a prospective cohort study including 1) patients with histologically proven SAR who were treatment-naïve at inclusion, 2) patients with microbiologically proven TB who were treatment-naïve at inclusion, and 3) healthy donors (HC). Patients infected with HIV or pregnant patients were excluded. Samples were collected before treatment and after 6 months of treatment. The NULISA method was used to study the level of 250 cytokines in plasma. An in-depth immunophenotyping of circulating cells was performed by spectral cytometry. Epigenomic (CUT&Tag) and transcriptomic (RNA-Seq) characterisation was performed on circulating monocytes. We targeted the epigenetic mark H3K27Ac, involved in trained immunity, to identify ‘super-enhancers’ and ultimately regulatory networks within monocytes.

Results: Patients with SAR (N=14, median age 48 years, 36% women) and TB (N=20, median age 40 years, 30% women) shared a common plasma protein signature with elevated plasma levels of chemokines (e.g., CXCL9, CXCL10, CXCL11) and pro-inflammatory cytokines (e.g., IFNg) compared to HC (N = 23, median age 36 years, 48% women), reflecting activation of the JAK-STAT signalling pathway and type II IFN. Immunophenotyping of circulating cells showed an increase in the proportion of non-classical monocytes (CD14+CD16++) in SAR compared to HC and TB patients. Transcriptomic analysis of circulating monocytes revealed 36 differentially expressed transcripts (DE, adjusted p-value < 0.05) between SAR and HC (e.g. STAT1, IRF1, JAK2, IL12RB1), 14 of which were also increased in TB (e.g. STAT1, IRF1); 111 transcripts were differentially expressed between SAR and TB (e.g. MAP4K1, FOS, SOCS3). As in plasma, activation of the JAK-STAT and type II IFN pathways was found in the monocytes of patients with SAR or TB compared to HC (adjusted p-value < 0.05). Within monocytes, there was also activation of various metabolic (e.g., oxidative phosphorylation) and epigenetic (e.g., histone 3 modifications) signalling pathways. The epigenetic signature of SAR monocytes was distinct from that of TB, with the identification of regions differently enriched in H3K27Ac (adjusted p-value <0.05, e.g. CCAT2, involved in cell proliferation and inhibiting apoptosis). There were different regulatory networks between SAR, TB and HC monocytes associated with transcriptional modifications (e.g. STAT1, IRF1, IRF8, MYC, FOSL2).

Conclusions: Our results show that trained immunity plays a different role in SAR and TB and attest to the uniqueness of the epigenetic signature carried by monocytes in SAR. These results open up new perspectives on the role played by trained immunity in the pathophysiology of SAR and, more broadly, in that of granulomatous diseases.

REFERENCES: NIL.

Acknowledgments: NIL.

Disclosure of Interests: None declared.