CXCR4 and systemic sclerosis: In summary, analyses of samples from IPF patients [9,19], SSc-ILD patients [13] and mice treated with bleomycin [8,18] (considered to be a model for both IPF and SSc-ILD) demonstrate the central role of the CXCL12/CXCR4 axis in the recruitment of fibrocytes into damaged lung tissue.