Pulmonary intravascular macrophages in deer.

Pulmonary intravascular macrophages (PIMs) have been found in the septal capillaries of deer lungs. Lung samples from adult deer were fixed in 2.5% glutaraldehyde, and then routinely processed for electron microscopy. The main features of the PIMs were the presence of tubular invaginations in the membrane (micropinocytosis vermiformis), phagosomes, and junctions with endothelial cells. A mean of 4.4 of these junctions was recorded per cell. They comprised segments ranging from 67 to 289 nm in length, where the plasma membranes were separated by spaces from 10 to 25 nm wide. In these areas the cytoplasm underlying the membranes showed evidence of increased electron density. When PIMs were compared with alveolar macrophages, it could be seen that although the PIMs were more numerous (more than twice), they were also smaller than the alveolar macrophages (47.625 versus 101.260 microns2 respectively.