Morphologic Characteristics of Pulmonary Macrophages in Cetaceans: Particular Reference to Pulmonary Intravascular Macrophages as a Newly Identified Type

Abstract

Abstract. We examined the morphologic characteristics of pulmonary macrophages in 42 specimens of Odontoceti (Globicephala macrorhynchus, Grampus griseus, Tursiops truncatus, Stenella attenuata, Stenella coeruleoalba, Berardius bairdii), using light and electron microscopes as well as immunohistochemistry with SRA-E5. SRA-E5-positive alveolar macrophages and pulmonary interstitial macrophages contained graphitic soots, indicating the clearance of airborne, aspirated foreign bodies. Pulmonary intravascular macrophages (PIMs), positive with SRA-E5, were present within pulmonary capillaries, attaching to applied endothelial cells by cell junctions. They showed cytoplasmic tubular structures of micropinocytosis vermiformis and erythrophagocytosis, indicating their contributory role in the clearance of blood-borne particles. The uptake of pathogens by PIMs may be associated with the inducement of acute lung injury, especially bacterial infectious pneumonia. This study revealed for the first time the presence of PIMs in cetaceans.Key words: Cetaceans; lung; morphology; pulmonary intravascular macrophage.Pathogens flowing in the blood stream, such as bacteria and endotoxins, aged erythrocytes, and cellular debris, are rapidly removed by macrophages. According to the mononuclear phagocyte system (MPS) theory, macrophages are mononuclear cells derived from the bone marrow, are resident cell types in contact with the blood circulatory system, and play an important role in host defenses. 1,21 Interestingly, it has been reported that MPS-derived cells, called pulmonary intravascular macrophages (PIMs), exist within pulmonary capillaries in the order Artiodactyla (cattle, goats, sheep, deer, and swine), in the order Perissodactyla (horses and burros), and in cats. 2,7,21 To our knowledge, however, there have been no reports on PIMs in cetaceans. We examined the detailed morphologic characteristics of resident macrophages in the lungs of cetaceans. This article is the first description of PIMs in cetaceans.We examined lung samples from 42 animals of Odontoceti caught for the purpose of fisheries by small-type whaling or hand-harpoon fisheries off the coast of Wakayama and Chiba prefectures in 2001-2003, Japan. Specimens comprised 16 Globicephala macrorhynchus, 12 Grampus griseus, six Tursiops truncatus, three Stenella attenuata, two Stenella coeruleoalba, and three Berardius bairdii (Table 1). These samples were provided for our study by the National Research Institute of Far Seas Fisheries, Japan. The age class (adult or immature) of animals was estimated on the basis of standard body length measurements. [8][9][10][11][12]14,15 One or two pieces (4 cm 3 ) of lungs were fixed by immersion in 10% neutral buffered formalin and Zamboni's solution and then embedded in paraffin. For light microscopy, sections were stained with hematoxylin and eosin (HE) and Berlin blue stain. The formalin-fixed lung tissues of G. macrorhynchus and G. griseus were postfixed in 1% osmium tetroxide and embedded in epoxy resin. Ultrathin sections wer...

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