C-X-C motif chemokine 13 (CXCL13) is a prognostic biomarker of idiopathic pulmonary fibrosis

Abstract

Rationale: C-X-C motif chemokine 13 (CXCL13) mediates B-cell trafficking and is increased, proportionately to disease activity, in many antibody-mediated syndromes. Dysregulated B cells have recently been implicated in idiopathic pulmonary fibrosis (IPF) pathogenesis.

Objectives: To determine if CXCL13 is associated with IPF progression.

Methods: CXCL13 was measured in lungs by DNA microarray and immunohistochemistry, and in plasma by ELISA.

Measurements and main results: CXCL13 mRNA was threefold and eightfold greater in IPF lungs (n = 92) compared with chronic obstructive pulmonary disease (COPD) (n = 191) and normal (n = 108) specimens, respectively (P < 0.0001). IPF lungs also showed increased CXCL13 staining. Plasma CXCL13 concentrations (pg/ml) were greater in 95 patients with IPF (94 ± 8) than in 128 subjects with COPD (53 ± 9) and 57 normal subjects (35 ± 3) (P < 0.0001). Circulating CXCL13 levels were highest in patients with IPF with pulmonary artery hypertension (P = 0.01) or acute exacerbations (P = 0.002). Six-month survival of patients with IPF in the highest quartile of plasma CXCL13 was 65 ± 10% versus 93 ± 10% in the others (hazard ratio, 5.5; 95% confidence interval, 1.8-16.9; P = 0.0008). CXCL13 increases by more than 50% in IPF serial assays, irrespective of initial values, also presaged respiratory failure (hazard ratio, 7.2; 95% confidence interval, 1.3-40.0; P = 0.008). In contrast, CXCL13 clinical associations in subjects with COPD were limited to modest correlations with FEV1 (P = 0.05) and progression of radiographic emphysema (P = 0.05).

Conclusions: CXCL13 is increased and is a prognostic biomarker in patients with IPF, and more so than in patients with COPD. This contrast indicates CXCL13 overexpressions are intrinsic to IPF, rather than an epiphenomenon of lung injury. The present data implicate CXCL13 and B cells in IPF pathogenesis, and support considerations for trials of specific B-cell-targeted therapies in patients with this intractable disease.

Figures

Figure 1.

(A) C-X-C motif chemokine 13 (CXCL13) in circulations of 57 normal control subjects (Nl), 128 subjects with chronic obstructive pulmonary disease (COPD), and 95 subjects with idiopathic pulmonary fibrosis (IPF). Horizontal lines from bottom to top denote 10th, 25th, 50th, 75th, and 90th percentiles. Mean values are denoted by solid squares. (B) CXCL13 mRNA expression in 108 normal control, 191 COPD, and 92 IPF lung specimens. (C) Intrapulmonary CXCL13 immunostaining. Analyses were performed on normal (upper left, n = 5) and IPF (upper right, n = 6) lungs. Asterisks denote fibroblastic foci in IPF lungs. A human lymph node was used as a positive control (lower left) and shows CXCL13 staining in a germinal center. CXCL13 immunostaining was readily observed in the loosely formed lymphoid aggregates in IPF lungs but was rare in normal lungs. In the upper panels, magnification is ×40, and the yellow inset bar represents 200 μm. In the lower panels, magnification is ×100, and the orange inset bar represents 100 μm.

Figure 2.

Most peripheral blood CD20+ B cells among both subjects with chronic obstructive pulmonary disease (COPD) and subjects with idiopathic pulmonary fibrosis (IPF) expressed C-X-C chemokine receptor 5 (CXCR5). There were no significant differences between COPD and IPF values.

Figure 3.

(A) The only statistically significant correlation among subjects with chronic obstructive pulmonary disease between circulating C-X-C motif chemokine 13 (CXCL13) levels and cross-sectional demographic or pulmonary function/radiographic characteristics at the time of specimen acquisitions (Table 1) was this inverse association of the chemokine concentrations with percent predicted values for FEV1. (B) Repeated clinical assessments were available in 91 subjects with chronic obstructive pulmonary disease approximately 2 years after their initial evaluations and CXCL13 specimen acquisitions. The only significant correlation of CXCL13 with changes in pulmonary measures over the next 2 years was an association with interval changes (delta) in the percentages of lung pixel values less than 910 Hounsfield Units (HU).

Figure 4.

(A) C-X-C motif chemokine 13 (CXCL13) concentrations were weakly correlated with diffusing capacities of carbon monoxide (DlCO) (ml/min/mm Hg), and (B) FVC (L) of subjects with idiopathic pulmonary fibrosis (IPF). (C) Subjects with IPF with pulmonary artery hypertension (PH, n = 15) have greater circulating CXCL13 levels than patients with normal pulmonary artery pressures (noPH, n = 23). PH is defined as pulmonary artery mean greater than 25 mm Hg with pulmonary artery wedge pressures less than 15 mm Hg. (D) CXCL13 concentrations were greatest among patients with IPF who were having, or going to have, AE in the next 6 months (n = 9). (E) Transplant-free survival (TFS) was worse among the subjects with IPF with the highest quartile of CXCL13. Numbers in parentheses denote censored events (end of observations). (F) Actuarial analyses with transplantations censored confirmed the absolute mortality was greatest among the quartile of subjects with IPF with the highest CXCL13 levels. Cross hatches and numbers in parenthesis denote censored subjects. AE = acute exacerbations; CI = confidence interval; HR = hazard ratio.

Figure 5.

(A) The greatest increases in circulating C-X-C motif chemokine 13 (CXCL13) concentrations from previous measures (as a percentage change) were seen among the 16 subjects with idiopathic pulmonary fibrosis (IPF) who subsequently developed respiratory failure (RF) that resulted in their deaths (n = 13) or requirements for emergent lung transplantations necessitated by life-threatening acute exacerbations (n = 3) (Yes), compared with the other 30 patients with IPF in the longitudinal cohort (No). (B) subjects with IPF in the highest quartile for increases in serial CXCL13 measures (n = 11) were more likely than the other patients with IPF in the longitudinal cohort (n = 35) to develop RF resulting in death or require emergent lung transplantation because of severe acute exacerbations. (C) Relative changes of plasma CXCL13 in later assay determinations were not significantly correlated with concentrations of this chemokine in the initial specimens obtained from the subjects with IPF at their study enrollment. CXCL13 increases of more than 50% in serial assays (dotted line) were predictive of poor outcomes (Figures 5A and 5B), and often occurred among subjects with low initial chemokine concentrations. CI = confidence interval; HR = hazard ratio.