A shared monocyte cytokine signature induced by serum from patients with systemic lupus erythematosus and anti-MDA5 antibody-positive dermatomyositis through the type I interferon pathway.

Objectives: To investigate the cytokine induction profile across multiple myeloid lineages by sera from patients with systemic lupus erythematosus (SLE) or polymyositis/dermatomyositis (PM/DM) using ex vivo whole blood stimulation assay and identify the signaling pathway relevant to monocyte cytokine signature.

Methods: Serum samples were obtained from adult patients with SLE, anti-melanoma differentiation-associated gene 5 (MDA5)-positive DM, anti-aminoacyl tRNA synthetase (ARS)-positive PM/DM, and healthy controls. Heparinized whole blood from healthy donors was incubated with serum, IFN-α, and IFN-β, followed by flow cytometric analysis. The expression of 9 cytokines was analyzed in CD14⁺ monocytes. The effect of upadacitinib preincubation on cytokine induction was evaluated. CD14⁺ monocytes isolated from healthy donors were incubated with serum or IFN-β, followed by bulk RNA sequencing.

Results: Active SLE and MDA5 sera induced a shared monocyte cytokine signature with upregulation of monocyte chemoattractant protein-1 (MCP1) and interleukin-1 receptor antagonist (IL-1RA) in CD14⁺ monocytes, whereas ARS and control sera did not. This monocyte cytokine signature closely resembled that induced by IFN-α and IFN-β. RNA-seq revealed 383 upregulated genes common to SLE serum, MDA5 serum, and IFN-β. Pathway analysis revealed that genes upregulated by exposure to SLE serum and MDA5 serum were predominantly involved in IFN-αβ signaling pathway. Upadacitinib abrogated the monocyte cytokine signature induced by SLE or MDA5 serum.

Conclusions: Serum from patients with active SLE and anti-MDA5+ DM can induce a shared monocyte cytokine signature, primarily through the IFN-αβ signaling pathway. CD14⁺ monocytes "primed" by serum may contribute to the pathogenesis of these diseases.