PRTN3 and interstitial lung disease: Based on the study area, subgroup analysis for the ACPA titer by region (divided into “foreign group” and “China group”) revealed that ACPA titer both in foreign and China populations was significantly related to the risk of RA-ILD, while there was no heterogeneity in the subgroup of foreign group (chi2 = 1.20, P = 0.55, I2 = 0%; random effects model).