Free iron concentrations (without prior acid digestion) were also examined but were not detected in IPF or healthy BAL supernatants (data not shown); however, we detected iron-containing AMs by Prussian blue staining of cytospin preparations (Figure 2D), and CD71+ AMs appeared to sequester more iron than their CD71− counterparts. This evidence concerns the gene TFRC and idiopathic pulmonary fibrosis.