White cells in the blood of Apennine brown bears: An ultrastructural study

White cells of peripheral blood are important in the reaction of the body to pathogens. Their morphology in the brown bear (Ursus arctos) has received little detailed attention. In this study, white cells were separated from 84-ml blood samples drawn from the jugular vein of six captive and three wild-caught bears (six Apennine brown bears from the Italian population, three of undetermined origin). As in most mammals, light and electron microscopy showed the presence of neutrophils, eosinophils, basophils, lymphocytes (some with natural killer features), and monocyte- macrophages. The differential count showed a slightly higher percentage of eosinophils than those observed in the mouse (Mus musculus) and rat (Rattus norvegicus), and in humans. Eosinophils displayed granules containing thinner and more stretched crystalloids than in the cat (Felis silvestris), mouse, and human. Both neutrophils and eosinophils contained numerous nonmembrane-bound inclusions in the cytoplasm that contained lipids (lipid bodies). The number of lipid bodies increased after incubation in 1.0 μM oleic acid. These findings suggest that in the brown bear, peripheral white blood cells also are involved in lipid metabolism as agents of transport and storage.