Biomarkers of rheumatoid arthritis-associated interstitial lung disease

Abstract

Objective: Interstitial lung disease (ILD) is a relatively common extraarticular manifestation of rheumatoid arthritis (RA) that contributes significantly to disease burden and excess mortality. The purpose of this study was to identify peripheral blood markers of RA-associated ILD that can facilitate earlier diagnosis and provide insight regarding the pathogenesis of this potentially devastating disease complication.

Methods: Patients with RA who were enrolled in a well-characterized Chinese identification cohort or a US replication cohort were subclassified as having RA-no ILD, RA-mild ILD, or RA-advanced ILD, based on high-resolution computed tomography scans of the chest. Multiplex enzyme-linked immunosorbent assays (ELISAs) and Luminex xMAP technology were used to assess 36 cytokines/chemokines, matrix metalloproteinases (MMPs), and acute-phase proteins in the identification cohort. Unadjusted and adjusted logistic regression models were used to quantify the strength of association between RA-ILD and biomarkers of interest.

Results: MMP-7 and interferon-γ-inducible protein 10 (IP-10)/CXCL10 were identified by multiplex ELISA as potential biomarkers for RA-ILD in 133 RA patients comprising the Chinese identification cohort (50 RA-no ILD, 41 RA-ILD, 42 RA-indeterminate ILD). The findings were confirmed by standard solid-phase sandwich ELISA in the Chinese identification cohort as well as an independent cohort of US patients with RA and different stages of ILD (22 RA-no ILD, 49 RA-ILD, 15 RA-indeterminate ILD), with statistically significant associations in both unadjusted and adjusted logistic regression analyses.

Conclusion: Levels of MMP-7 and IP-10/CXCL10 are elevated in the serum of RA patients with ILD, whether mild or advanced, supporting their value as pathogenically relevant biomarkers that can contribute to noninvasive detection of this extraarticular disease complication.

Figure 1

Serum levels of matrix metalloproteinase 7 (MMP-7) and interferon-γ–inducible protein 10 (IP-10) in rheumatoid arthritis (RA) patients in the Chinese identification cohort (A) and the US replication cohort (B) without interstitial lung disease (ILD) or with different stages of ILD. Dot plots depict levels (measured by standard solid-phase enzyme-linked immunosorbent assay) of MMP-7 or IP-10 in individual serum samples from RA patients without ILD (interstitial lung abnormality [ILA] score 0), indeterminate ILD (ILA score 1), mild ILD (ILA score 2), or advanced ILD (ILA score 3). Samples from patients with ILA scores of 2 or 3 were further stratified into groups of subclinical ILD versus clinically evident/symptomatic ILD (based on the presence of cough and/or dyspnea). Each symbol represents an individual patient; horizontal lines show the mean. P values were determined by Mann-Whitney U test.

Figure 2

Performance characteristics of biomarker levels in RA-ILD. For both the Chinese identification cohort (A) and the US replication cohort (B), receiver operating characteristic curves (shown as area under the curve [AUC]) demonstrate the predictive capacity of MMP-7 level, IP-10 level, rheumatoid factor (RF) titer, and anti–cyclic citrullinated peptide (anti-CCP) titer for the presence of RA-ILD. Ninety-five percent confidence intervals are shown in parentheses. See Figure 1 for other definitions.

Figure 3

Relationship between biomarker levels and pulmonary function parameters. A and B, Relationship between levels of IP-10 or MMP-7 and pulmonary function parameters (forced vital capacity [FVC] and diffusing capacity for carbon monoxide [DL_CO] [both measured as the percent predicted]) in the Chinese identification cohort (A) and the US replication cohort (B). C, Relationship between mean serum levels of IP-10 or MMP-7 and the dyspnea score in the US cohort. For all analyses, Spearman’s rank correlation coefficients (rho values) indicate the relative magnitude and direction of covariation between biomarker levels and pulmonary function parameters or dyspnea score. * = P < 0.05. See Figure 1 for other definitions.