CD33 and idiopathic pulmonary fibrosis: Our study did not show any differences in CXCR4+/CD19+ (B-cell origin) or CXCR4+/CD33+ (early myeloid origin) cells, and therefore further investigation with a larger panel of surface markers may be necessary to delineate whether other circulating CXCR4+ cells are clinically relevant in IPF.