Viral infections
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Viral infections of the lung usually produce either a chronic interstitial pneumonitis (as shown here) or diffuse alveolar damage. The inflammatory reaction is predominantly interstitial (within the walls of alveoli) rather than in alveolar spaces. The inflammatory infiltrate is composed of lymphocytes, occasional plasma cells and histiocytes. In this slide, notice the interstitial location of the chronic inflammatory infiltrate with relatively sparse numbers of cells in alveolar spaces.