The number of ICAM–1 negative alveolar macrophages is significantly higher in NC (median 42,969 cells per mm2, range 14,497–150,936 cells per mm2) compared to IPF (median 2891 cells per mm2, range 0–39,443 cells per mm2, p = 0.0004) (Figure 4D). Here, ICAM1 is linked to idiopathic pulmonary fibrosis.