The fibrogenic chemokine CCL18 is associated with disease severity in Erdheim-Chester disease

Abstract

Erdheim-Chester disease (ECD) is a rare histiocytosis, characterized by xanthogranulomatous tissue infiltration by foamy histiocytes. Fibrosis, a histologic hallmark of ECD, is responsible for lesion growth and clinical manifestations. Unraveling molecular fibrotic pathway in ECD would allow the identification of new pharmacologic targets. In this study, we evaluated serum and tissue samples from a large cohort of ECD patients focusing on two major pro-fibrotic mediators, TGF-β1 and chemokine ligand 18 (CCL18). We found a marked increase in CCL18 but not TGF-β1 levels in serum and lesions of ECD patients (p < 0.001), independently of treatment status and consistently over time. Using a linear mathematical model, we also found that elevated CCL18 serum levels correlate with both number and severity of disease localizations. These findings suggest the involvement of CCL18-induced fibrosis in ECD pathogenesis, providing a rationale for exploring CCL18 inhibition as a treatment for progressive fibrosis in ECD.

Keywords: CCL-18; Erdheim-Chester disease; fibrosis.

Figure 1.

Serum and tissue levels of TGF-β1 and CCL18 in ECD patients. (A) Mean ± SEM plasma levels of TGF-β1 in ECD patients and healthy controls. (B) Mean ± SEM plasma levels of CCL18 in ECD patients and healthy controls. (C) Mean ± SEM plasma levels of CCL18 in treated and untreated ECD patients as compared to healthy controls. Groups were compared using unpaired Student's t-test, data are expressed as mean ± SEM of 20 ECD patients and 20 controls. (D) Expression of TGF-β1 and CCL18 was evaluated in different ECD lesions with immunohistochemistry. Panels D and E show microphotographs of representative lesions (skin biopsies). (D) Immunohistochemical assessments do not show a significant intra-lesional expression of TGF-β1. (E) CCL18 is markedly expressed by macrophages, with cytoplasmic reactivity and a particular reinforcement of the Golgi apparatus. Immunohistochemistry for TGF-β1 and CCL18 was performed with diaminobenzidine and background staining with hematoxylin; original magnification 200 ×. ECD Erdheim-Chester disease, HC healthy control, Utx untreated patients, Tx treated patients; ns non-significant, *p<0.05, **p<0.005, ***p<0.001.

Figure 2.

Correlation between CCL18 levels and other variables in ECD patients. Graphic representation of the analysis performed using univariate linear model. The color scale ranges from 1 (correlation coefficient ρli = 1, correlation of the direct type) to -1 (correlation coefficient ρ1, = -1, correlation of the indirect type). A weak correlation is represented with 0<ρ-1<0.3, a moderate correlation with 0.3 <ρ0. <0.7 and a strong correlation with ρ<0> 0.7. The correlation index is 0 if the two variables are independent. The barred boxes represent the pairs of variables whose correlation does not result to be statistically significant with α = 0.05. There is a statistically significant positive correlation between the variables CCL18 and LocCNS and between CCL18 and Locations. IL-6 Interlukin 6, MCP-1 Monocyte chemoattractant protein-1, IL-8 Interlukin 8, ESR Erythrocyte sedimentation rate, MIP-1β Macrophage inflammatory protein-1 beta, DoD Duration of disease, IP-10 Interferon gamma-induced protein 10, LocCt Cutaneous localization, TGF- β transforming growth factor beta, IL-12 Interlukin 12, LocCNS Central nervous system localization, Loc Localisation, CCL18 Chemokine ligand 18, CRP C reactive protein.