| Abstract: | Intravascular macrophages were found commonly in sections of calf lung capillaries. These cells were large with many pseudopodia of various sizes. The cell membrane was covered with an electron-opaque coat which remains between adjacent pseudopodial walls and results in structures suggesting “micropinocytosis vermiformis.” The cytoplasm of the macrophage was electron-lucent and contained endoplasmic reticulum, numerous mitochondria, free ribosomes, Golgi zones, dense bodies and vesicles of many sizes. These macrophages showed phagocytic activity. During erythrophagocytosis, a dense layer initially appeared at the red blood cell periphery. This layer moved toward the center together with the erythrocyte membrane as phagocytosis progressed. Simultaneously, the electron opacity of the red blood cell decreased until the cell was completely dispersed within the macrophage. This erythrophagocytosis occurred relatively seldom. The possibility that intravascular macrophages are the pre-cursors of alveolar macrophages is discussed. |
