Anti-RNA binding protein positivity in idiopathic interstitial pneumonia.

INTRODUCTION: Idiopathic interstitial pneumonias (IIP) are diffuse lung diseases whose cause is unknown and often present with features of autoimmunity despite not meeting criteria for a connective tissue disease (CTD). Recent studies suggest that anti-RNA binding protein (anti-RBP) antibodies, which include anti-SSA, anti-SSB, anti-Sm, and anti-RNP, play a role in the loss of immune tolerance and severity of pulmonary hypertension (PH) in CTDs. We hypothesized that anti-RBP positive (RBP+) subjects would have worse measures of lung function, radiographic findings, PH, and survival than anti-RBP negative (RBP-) subjects.

METHODS: Subjects with both IIP and serologies for review were identified retrospectively and stratified based on anti-RBP antibody seropositivity. Baseline cohort characteristics, pulmonary function tests (PFT), ambulatory oxygen requirement, radiographic characteristics, markers of PH, and transplant-free survival were compared between anti-RBP positive and negative groups.

RESULTS: Five hundred twenty patients with IIP were identified, of which ten percent (n = 53) were anti-RBP positive. RBP+ as compared to RBP- subjects had significantly worse PFTs as indicated by FEV1 (59.6 vs. 64.9, p = 0.046) and FVC (71.6 vs. 78.8, p = 0.018). There was a higher prevalence of radiographic honeycombing (49.1% vs. 38.3%, p = 0.006) and emphysema (22.6% vs. 5.1%, p < 0.001) in the RBP+ group despite no difference in smoking history. The Pulmonary Artery-Aorta ratio was also larger in the RBP+ group (0.93 vs. 0.88, p = 0.040). There was no difference in transplant-free survival between groups (log rank = 0.912).

CONCLUSION: Anti-RBP+ IIP patients may have worse lung function, increased chest radiographic abnormalities, and PH compared with those without these antibodies.