A silicotic nodule in lung is seen here. It is composed mainly of bundles of interlacing pink collagen. There is a minimal inflammatory reaction.

Anthracotic pigment ordinarily is not fibrogenic, but in massive amounts (as in "black lung disease" in coal miners) a fibrogenic response can be elicited to produce the "coal worker's pneumoconiosis" seen here.

This idiopathic condition is characterized by granuloma formation. The granulomas

Sarcoidosis are typically non-caseating. Hilar lymph nodes are nearly always involved and can become quite large

At low magnification can be seen multiple small granulomas in this case of sarcoidosis. These numerous interstitial granulomas can produce a restrictive lung disease.

The acute intra-alveolar hemorrhage seen here is a consequence of capillary injury from basement membrane antibody in a patient with Goodpasture syndrome. The glomerular capillaries are targeted as well, leading to a rapidly progressive glomerulonephritis. Circulating anti-glomerular basement membrane antibody can be detected.

In this is an example of hypersensitivity pneumonitis that has become more chronic, a granulomatous type of inflammation is present, indicative of a type IV hypersensitivity reaction.

This is hypersensitivity pneumonitis, a type of interstitial pneumonitis also known as extrinsic allergic alveolitis because it occurs when there is an inhaled organic dust that produces a localized for of type III hypersensitivity (Arthus) reaction from antigen-antibody complexes.