Antibodies against chemokine receptors CXCR3 and CXCR4 predict progressive deterioration of lung function in patients with systemic sclerosis

Background: The chemokine receptors CXCR3 and CXCR4 are involved in the pathogenesis of fibrosis, a key feature of systemic sclerosis (SSc). It is hypothesized that immunoglobulin (Ig)G antibodies (abs) against these two receptors are present in patients with SSc and are associated with clinical findings. Methods: Anti-CXCR3 and anti-CXCR4 ab levels were measured in 449 sera from 327 SSc patients and in 234 sera from healthy donors (HD) by enzyme-linked immunosorbent assay (ELISA). In SSc, ab levels were compared with clinical data in a cross-sectional and longitudinal setting. Protein expression of CXCR3 and CXCR4 on peripheral blood mononuclear cells (PBMCs) was analyzed in 17 SSc patients and 8 HD by flow cytometry. Results: Anti-CXCR3 and anti-CXCR4 ab levels were different among SSc subgroups compared with HD and were highest in diffuse SSc patients. The ab levels strongly correlated with each other (r = 0.85). Patients with SSc-related interstitial lung disease (SSc-ILD) exhibited higher ab levels which negatively correlated with lung function parameters (e.g., r = -0.5 and r = -0.43 for predicted vital capacity, respectively). However, patients with deterioration of lung function showed lower anti-CXCR3/4 ab levels compared with those with stable disease. Frequencies and median fluorescence intensities (MFI) of CXCR3 ⁺ and CXCR4 ⁺ PBMCs were lower in SSc patients compared with HD and correlated with the severity of skin and lung fibrosis. They correlated with the severity of skin and lung fibrosis. Conclusions: Anti-CXCR3/4 abs and their corresponding receptors are linked with the severity of SSc-ILD. Antibody levels discriminate patients with stable or decreasing lung function and could be used for risk stratification.