Figure 2a. Histologic features of UIP. (a) Photomicrograph (original magnification, x40; hematoxylin-eosin stain) shows patchy fibrosis with remodeling of the lung architecture. Interstitial chronic inflammation is mild, with only a few lymphoid aggregates (thin arrow). Cystically dilated airspaces that produce a honeycomb pattern (arrowhead) and areas of relatively unaffected lung (thick arrow) are present. (b) Photomicrograph (original magnification, x200; hematoxylin-eosin stain) shows a fibroblastic focus of loose organizing connective tissue (arrowheads), which is the hallmark of UIP.