Mitosis of type B alveolar cells in the early hyperplastic response to Freund's adjuvant

Numerous areas of granulomatous inflammation develop in the lungs of rabbits following the intravenous injection of Freund's complete adjuvant (FCA). Within a few days after FCA injection, hyperplasia of type B (type I) alveolar cells is present on the surface of the septa in which an inflammatory reaction is developing. Mitosis of type B cells is detected 12 h after FCA injection and is common over the next 120 h. In addition, there are morphologic changes that are consistent with migration of these cells. The type B cells in mitosis extend across alveolar septa as well as along the alveolar surface. The extension of type B cells through alveolar septa is not limited to cells in mitosis, but is also observed in non-mitotic type B cells. Stimulation of mitosis and hyperplasia of type B cells is discussed in relation to the focal tissue injury and inflammatory response.