Figure 1: CCL19+ proinflammatory fibroblasts recruited CCR7+ T cells interacting with fibroblasts in SSc. A, Schematics of our experimental design. B, Visualization of the distribution of fibroblasts from control and SSc skin samples, visualized by UMAP, with fibroblasts colored by subset as shown in the key. C, Visualization of the distribution of fibroblasts from control and SSc skin samples visualized by UMAP, with cells colored by condition as shown in the key. D, Fraction of CCL19+ fibroblast in healthy and SSc skin. Wilcox test p value is shown (**p<0.01, *p<0.05). E-G, Fraction of CCL19+ fibroblast in healthy and SSc individuals with or without disease complications, including articular symptoms E; interstitial lung disease F; and digital ulcer G in the dataset of Amit, et al. H, Upregulated GO:BP pathways in CCL19+ fibroblasts from SSc skin compared to healthy skin. I, Representative staining for CCL19 and vimentin in healthy skin and SSc immune niches. Scale bar, 50 μm. J Fraction of CCL19+ fibroblast in dermal niches of patients with SSc (n=21) and controls (n=12). Two-tailed Welch’s t-test p value is shown. K Comparison of the significant ligand-receptor pairs between healthy individuals and SSc skin contributes to the signaling from CCL19+ fibroblast to T cells. Dot color reflects communication probabilities and dot size represents computed p values. Empty space means the communication probability is zero. p values are computed from the one-sided permutation test. L, Representative staining for CCR7 in T cells in healthy skin and SSc immune niches. Scale bar, 50 μm. M, Proportions of CCR7+T cells in immune niches in patients with SSc (n=16) and controls (n=8). Two-tailed Welch’s t-test p value is shown (*p<0.05). N, Significant decrease of CCR7+ T cells in SSc (n = 9) PBMC compared to healthy control (n = 4) by flow cytometry. Two-tailed Welch’s t-test p value is shown (**p<0.01). O, Pseudo-time analysis of CCR7+ T cells from skin and PBMC in healthy and SSc individuals. P, Pseudotime trajectory of CCR7+ T cell from PBMC and skin in healthy and SSc individuals. Q, Ratio of 'pre-branch', 'infiltrating' and 'circulating' branches in CCR7+ T cells of SSc compared to healthy individuals. R, The proportion of CCR7+ T cells in healthy and SSc skin CD4+ T cells and CD8+ T cells. S, Stemness score of CD4+CCR7- and CD4+CCR7+ T cells. T, Stemness score of CD8+CCR7- and CD8+CCR7+ T cells. U, Circos plot showing the differential number of interactions from CD8+CCR7+ T cells to fibroblast subsets in SSc skin compared to healthy skin. V, Circos plot showing the differential number of interactions from CD4+CCR7+ T cells to fibroblast subsets in SSc skin compared to healthy skin.

Figure 2: Disrupting the CCL19-CCR7 axis reduces dermal T cell infiltration and fibrosis in vivo.
A, Schematic representation of the in vivo experiment. n = 4 mice in PBS and isotype antibody treated bleomycin group, n = 5 mice in anti-CCL19 antibody treated group. B, Representative H&E staining (top) and Masson staining (below) of the mice skin from the groups of mice depicted in A. Scale bar, 100 μm. C-E, Quantitative analysis of dermal thickness determined by H&E staining (μm) (C), collagen volume fraction calculated from Masson staining images, expressed as a percentage of the total dermis volume (D) and relative mRNA expression of Col1a1 (E). F, Representative staining for CD3, F4/80 and CCR7 in mice skin. Scale bar, 50 μm. G, Proportions of CD3+ T cells and F4/80+ macrophages in mice skin with or without bleomycin injection. H, Proportions of CD3+ T cells and CCR7+ CD3+ T cells in the skin of bleomycin-treated mice receiving isotypic or anti-CCL19 antibodies. I, Outlines of the design in wild-type and Ccr7-/- mice following bleomycin-induced dermal fibrosis. n = 5 mice in the WT control group and n = 4 in the Ccr7-/- control group. On day 14 of bleomycin injection, n = 5 mice in the WT and Ccr7-/- groups. On day 21 of bleomycin injection, n = 4 mice in the WT group and n = 3 in the Ccr7-/- group. J, Representative images of H&E and Masson staining of the skin of WT and Ccr7-/- mice. Scale bar, 100 μm. K-M, Quantitative analysis of dermal thickness (μm) (K), collagen volume fraction (L) and relative mRNA expression of Col1a1 (M). Data presented above are expressed as Mean ± SEM. p values were measured by one-way ANOVA and Holm-Šídák multiple comparisons test. *p < 0.05, **p < 0.01, ***p < 0.001 and ****p < 0.0001.

Figure 3: Model of CCL19+ fibroblasts orchestrate fibrotic microenvironment via CCL19-CCR7 axis in systemic sclerosis.
The unique fibrotic microenvironment linking immunopathology and fibrosis, defined as immune niches, is enriched in the affected dermis of SSc. VEGFA induces CCL19-expressing proinflammatory fibroblasts under vascular dysfunction. These proinflammatory fibroblasts continuously generate immune niches through chemokine secretion and recruitment of immune cells from peripheral blood, particularly CCR7+ T cells. These recruited T cells can subsequently interact with fibroblasts within the immune niches, establishing a positive feedback loop that drives the fibrosis progression. Created with BioRender.com.