PTPRC and idiopathic pulmonary fibrosis: Alveolar fibrocytes, defined as cells expressing CD45 and collagen 1, were detected in 14/26 patients in the IPF group (53%), in 5/9 patients in the SSc-ILD group (55%) and in 0/11 controls (p = 0.006 and p = 0.02 versus controls, respectively).