Background/Purpose: Systemic juvenile idiopathic arthritis (SJIA) with macrophage activation syndrome (MAS) involves severe systemic inflammation and hepatocellular injury. Our prior histopathology studies showed increased CD8⁺ T cell and CD163⁺ macrophages in SJIA-MAS compared to SJIA without MAS (1). However, distinguishing SJIA-MAS liver involvement from autoimmune hepatitis (AIH), familial hemophagocytic lymphohistiocytosis (FHLH), and steatohepatitis (SH) remains challenging. We aimed to define spatial immune signatures across SJIA-MAS, AIH, FHLH, SH, and healthy controls (HC) using spatial transcriptomics with the ultimate goal to develop diagnostic biomarkers for clinical practice.

Methods: Formalin-fixed, paraffin-embedded liver tissues from SJIA-MAS (n=6), SJIA without MAS (n=1), AIH (n=7), FHLH (n=6), SH (n=5), and HC (n=6) were analyzed using the NanoString GeoMx DSP® platform. Immunofluorescent staining for CD18, CD68, CDE, and nuclear DNA was used to select regions of interest (ROIs) enriched for (1) hepatocytes; (2) macrophages, and (3) lymphocytes. Spatially resolved gene expression was Q3 normalized. In the initial analysis, levels of expression of the IFN-induced signature genes (ISG) as well as markers specific for CD4+ T cells, cytotoxic T cells (CD8, GZMb, PRF) and macrophages (CD163) were compared between the clinical groups in macrophage- and T cell-enriched compartments.

Results: SJIA-MAS samples showed strong interferon-stimulated gene (ISG) activation (STAT1, EPSTI1, CXCL9) in both macrophage and T lymphocyte enriched ROIs and higher expression of cytotoxic markers (GZMB), particularly in T cell–enriched areas, compared to mild ISG activation in SJIA without MAS (figure 1). AIH samples exhibited heterogeneous immune profiles with variable but modest CD4⁺ T cell expression with less prominent ISG (figure 2). FHLH shared partial interferon signatures but had lower overall ISG expression. LY6E was selectively elevated in FHLH macrophages (table 1).

Conclusion: SJIA-MAS is defined by activation and expansion of CD8⁺ T cells in addition to strong type I/II interferon responses, distinct from SJIA without MAS, AIH, and FHLH. Particularly high expression of CXCL9 distinguished SJIA-MAS. This suggests that serum CXCL9 may help distinguish MAS-related liver injury from other SJIA-associated pathologies. Global gene expression analysis in the same samples is ongoing.

Figure 1 Heatmap showing differential expression of interferon-stimulated genes and genes and T cell markers between SJIA-MAS and SJIA without MAS

Figure 2 Heatmap showing differential expression of interferon-stimulated genes and genes and T cell markers between autoimmune hepatitis and SJIA-MAS

Table 1. Spatial expression of immune markers across SJIA-MAS, SJIA without MAS, AIH, and FHLH. SJIA-MAS shows high ISG and cytotoxic signatures; other groups display lower or variable expression

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/spatial-transcriptomic-profiling-reveals-interferon-activation-and-cd8%e2%81%ba-t-cell-dominance-in-systemic-juvenile-idiopathic-arthritis-macrophage-activation-syndrome-liver-inflammation/