Lack of Fc receptors on osteoclasts

Fc and C3 receptors, which are characteristically present on macrophages, could not be demonstrated on osteoclasts maintained in situ on their normal substrates when assayed for by use of sheep red blood cells coated with immunoglobulin (Shapiro et al. 1979). The present study tested the hypotheses that Fc receptors are present only on the osteoclast surface adjacent to bone and that Fc receptors on osteoclasts can be uncovered by enzymes or stimulated to appear. Freeze-dried, inverted osteoclasts (and osteoblasts) obtained from the endocranium of newborn rats were tested for Fc receptors using the rosette assay and examined by scanning electron microscopy. No rosettes were observed on the surfaces of the osteoclasts that had been approximal to the bone. Bone specimens were cultured for 30 min at 37 degrees C in control medium, or in medium with the addition of 10, 50 or 100 microgram/ml trypsin, 0.5 U/ml parathyroid extract (PTE), or 0.5 or IU/ml parathyroid hormone 1--34 (PTH). Additionally, two week-old rats were injected intraperitoneally with PTE (1.5 U/g body weight or 1 USP/g body weight) or with PTH (1 U/g body weight) or with vehicle alone, 6 h before sacrifice. The specimens were assayed for Fc receptors and examined by scanning electron microscopy. Macrophages were always used as controls for the assay. No rosettes were present on osteoclasts subjected to any of these treatments. Accordingly, the hypotheses were not supported.