Anti-RNA binding protein positivity in idiopathic interstitial pneumonia

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.

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.

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).

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