Characterisation of macrophage infiltration and polarisation based on integrated transcriptomic and histological analyses in Primary Sjögren’s syndrome

Abstract

BackgroundPrimary Sjögren’s syndrome (pSS) is a progressive inflammatory autoimmune disease. Immune cell infiltration into glandular lobules and ducts and glandular destruction are the pathophysiological hallmarks of pSS. Macrophages are one of the most important cells involved in the induction and regulation of an inflammatory microenvironment. Although studies have reported that an abnormal tissue microenvironment alters the metabolic reprogramming and polarisation status of macrophages, the mechanisms driving macrophage infiltration and polarisation in pSS remain unclear.MethodsImmune cell subsets were characterised using the single-cell RNA sequencing (scRNA-seq) data of peripheral blood mononuclear cells (PBMCs) from patients with pSS (n = 5) and healthy individuals (n = 5) in a public dataset. To evaluate macrophage infiltration and polarisation in target tissues, labial salivary gland biopsy tissues were subjected to histological staining and bulk RNA-seq (pSS samples, n = 24; non-pSS samples, n = 12). RNA-seq data were analysed for the construction of macrophage co-expression modules, enrichment of biological processes and deconvolution-based screening of immune cell types.ResultsDetailed mapping of PBMCs using scRNA-seq revealed five major immune cell subsets in pSS, namely, T cells, B cells, natural killer (NK) cells, dendritic cells (DCs) and monocyte-macrophages. The monocyte-macrophage subset was large and had strong inflammatory gene signatures. This subset was found to play an important role in the generation of reactive oxygen species and communicate with other innate and adaptive immune cells. Histological staining revealed that the number of tissue-resident macrophages was high in damaged glandular tissues, with the cells persistently surrounding the tissues. Analysis of RNA-seq data using multiple algorithms demonstrated that the high abundance of pro-inflammatory M1 macrophages was accompanied by the high abundance of other infiltrating immune cells, senescence-associated secretory phenotype and evident metabolic reprogramming.ConclusionMacrophages are among the most abundant innate immune cells in PBMCs and glandular tissues in patients with pSS. A bidirectional relationship exists between macrophage polarisation and the inflammatory microenvironment, which may serve as a therapeutic target for pSS.

Advances in cellular and molecular pathways of salivary gland damage in Sjögren’s syndrome

“…Studies have shown that macrophage are consistently present in the affected SG of SS patients and their abundance is positively correlated with the focality index. Activated macrophage produce inflammatory cytokines that result in damage to SGECs ( 113 ). macrophage exhibit high plasticity, differentiating into either classically activated (M1 type) or alternatively activated (M2 type) macrophage in response to various microenvironmental stimuli.…”

The role of M1/M2 macrophage polarization in primary Sjogren’s syndrome

“…Human studies have provided evidence of macrophage infiltration in the salivary glands of pSS patients, which has been correlated with disease severity [ 2 , 3 ]. Analysis of single-cell RNA sequencing data demonstrated that macrophages are among the most abundant innate immune cells in peripheral blood mononuclear cells (PBMCs) and glandular tissues in pSS patients [ 4 ]. Additionally, research conducted using murine models of pSS suggests that macrophages may act as a mediator between CD4 + T cells and local tissue damage [ 5 , 6 ].…”