The picture on the left shows a section of healthy lung tissue, the leukocytes (M = macrophages) are all confined to the tissue; (E=endothelial cells), (C=capillary) and (P=pericyte).

The picture on the right shows a section of inflammed lung tissue, the leukocytes (M=macrophages) have migrated to the alveoli and therefore are inhibiting breathing.

^{_{(B. H. Wheater PR, Daniels VG, Functional Histology, Churchill Livingstone, Edinburgh, 1979 and B. H. Wheater PR, Stevens A, Lowe JS, Basic Histopathology, Churchill Livingstone, Edinburgh, 1991)}}