An ultrastructural examination of murine alveolar macrophages following intranasal administration of propionibacterium acnes.

Light and electron microscopic analysis of murine lungs or isolated pulmonary cells was performed three days after intranasal administration of the bacterial immunostimulant, Propionibacterium acnes (P. acnes). Our observations indicated that pulmonary alveolar and airway macrophages (PAMs) were the only cells with P. acnes bacilli in their cytoplasm. Bacilli were not observed in pulmonary interstitial macrophages, granulocytes, lymphocytes or pulmonary parenchymal cells such as type I and type II pneumocytes. Because of the morphological heterogeneity of PAMs observed in control and experimental animals, it was not possible from these studies to be certain about the relative abundance or complexity of lysosomes, endoplasmic reticulum, Golgi and other organelles in the two groups. However, we noted that it was not uncommon to observe in the same PAM, profiles of P. acnes and a well developed Golgi complex and endoplasmic reticulum. These P. acnes--associated morphological alterations occurred at a time when functional activities (e.g., phagocytosis, cytostasis) of PAMs were enhanced.