Fig. (4) Increases in TRAP staining of primary osteoclasts were stimulated with either metal implant debris directly or with the supernatants from implant-debris-activated-monocytes/macrophages. (A-C) The results indicated highly variable individual responses where only two individuals had significant increases in the amount of osteoclast TRAP staining when treated with metal ion supernatants of monocytes/macrophages-treated cell (from the same individual). (D) However when this behavior was averaged for n=3 individuals this increase was not apparent, given the variability in responses. And while there was on average 2-fold greater increase in TRAP positive staining for the osteoclasts treated with Co ions than (directly or with supernatants) vs Co-alloy particles, these increases were not significant (except for LPS, p=0.07, t-test). Monocytes/macrophages were isolated from human PBMCs and divided in two portions. The osteoclasts were challenged for 24 hours, and average TRAP staining was measured via optical density (OD)/well. Note: M-Supernatant indicates Monocyte/macrophage-supernatant (treated for the prior 24 hours with either Co ions or particles or LPS).