Duckling Lameness Provides Insight into Osteoclast Biology-I. Cytology

Abstract

Large multinuclear cells, osteoclasts, were detected in bone marrow touch preparation smears by light microscopy using Wright-Giemsa stain. They are from femur samples of lame ducklings between 7 and 29d. Osteoclasts were found in bone marrow proper, in areas populated mostly by erythroid and granulocytic developmental stages. These are located far from their usual place in situ (Howship’s lacunae) as a component of the basic multicellular unit. Thus, they are called ex situ types. Many are giants containing up to 50 nuclei of varying sizes. A single OC could contain a few small nuclei with areas (AN ~ 30 μm2) presumed as standard diploid types (2C). However, a majority of the nuclei are larger (AN >1.6 x 30 μm2) polyploids and aneuploid types. Nuclei may be located in restricted places (polarized) or uniformly distributed throughout the cytoplasm. Each nucleus contained up to 3 nucleoli themselves of varying size. The OC cytoplasm contains magenta or scarlet-colored “specific granules”, presumably representing tartrate resistant acid phosphatase (TRAP), and (transcytotic) vacuoles; both characteristics of secretory cells. Examples of phagocytic types, faint nuclear types, and anuclear types were detected in the same preparation. In some instances, the OC showed signs of nuclear degradation and cytoplasmic fractures (necrosis). Interestingly, some OC contained engulfed cells appearing normal and were not apoptotic. These are likely examples of emperipolesis. Other engulfed cells showed signs of deterioration due to phagocytosis. It is not yet known if these OC cells represent escapees from the BMU or are formed locally by the fusion of precursors. It is unknown if such cells are homeostatic or pathologic but based on their peculiar cytology the latter seems more likely. These observations are the first report.