Human osteoblast-like cells phagocytose metal particles and express the macrophage marker CD68 in vitro

Abstract

P eriprosthetic osteolysis is a major cause of aseptic loosening in artificial joint replacement. It is assumed to occur in conjunction with the activation of macrophages. We have shown in vitro that human osteoblast-like cells, isolated from bone specimens obtained from patients undergoing hip replacement, phagocytose fine particles of titanium alloy (TiAlV).The human osteoblast-like cells were identified immunocytochemically by the presence of bone-specific alkaline phosphatase (BAP). With increasing duration of culture, a variable number of the osteoblastic cells became positive for the macrophage marker CD68, independent of the phagocytosis of particles, with a fine granular cytoplasmic staining which was coexpressed with BAP as revealed by immunodoublestaining. The metal particles were not toxic to the osteoblastic cells since even in culture for up to four weeks massively laden cells were vital and had a characteristic morphology. Cells of the human osteosarcoma cell line (HOS 58) were also able to phagocytose metal particles but had only a low expression of the CD68 antigen. Fluorescence-activated cell scanning confirmed our immunocytochemical results. Additionally, the cells were found to be negative for the major histocompatibility complex-II (MHC-II) which is a marker for macrophages and other antigen-presenting cells. Negative results of histochemical tests for tartrate-resistant acid phosphatase excluded the contamination by osteoclasts or macrophages in culture.Our observations suggest that the osteoblast can either change to a phagocytosing cell or that the phagocytosis is an underestimated property of the osteoblast. The detection of the CD68 antigen is insufficient to prove the monocytic lineage. In order to discriminate between macrophages and osteoblasts additional markers should be used. To our knowledge, this is the first demonstration of cells of an osteoblastic origin which have acquired a mixed phenotype of both osteoblasts and macrophages. Received 17 December 1998; Accepted after revision 21 May 1999Resorption of the surrounding bone is commonly associated with aseptic loosening of artificial joints.1-4 Particles of titanium, a common material used for endoprostheses, are released from the surfaces into the surrounding tissue by corrosion or wear. 3,4 The release of particulate wear debris is generally accepted to be responsible for the recruitment of monocytes/macrophages and the formation of foreign-body granulomas. Phagocytosis of wear particles by macrophages stimulates these cells to produce and secrete inflammatory mediators 5,6 which have been implicated in the stimulation of bone resorption. 7,8The role of osteoblasts in contact with wear particles is poorly understood. We have investigated the behaviour of cultured human osteoblast-like cells when exposed to metal particles in vitro. To exclude the presence of cells of myeloid origin, we also studied markers such as CD68, tartrate-resistant acid phosphatase (TRAP) and major histocompatibility complex II (MHC II). CD68 is used a...

Phagocytosis and Allogeneic T Cell Stimulation by Cultured Human Osteoblast-Like Cells

“…Our results showed that phagocytosed particles are incorporated into the cytoplasm. No particles were found in the nucleus, consistent with findings of other authors [13,14]. The number of particles incorporated into the cells varied with the type of particle.…”

“…The particulates studied were synthesized polymers and wear debris from prosthetic materials of different composition. In general, small phagocytosed particles were described, with a mean size of 1 -3 µm diameter [11,13,14]. Our results showed that phagocytosed particles are incorporated into the cytoplasm.…”

Cobalt ions induce chemokine secretion in primary human osteoblasts

“…35 Human primary osteoblasts are capable of particle phagocytosis, which has been shown to lead to altered gene expression. 60,62,65,66 However, other studies have demonstrated that increased chemokine secretion also occurs independent of phagocytosis, suggesting that particle-cell contact and/or exposure to ionic dissolution products from the wear debris may have a role to play in periprosthetic osteolysis. 12,62 Our study clearly shows that cobalt in ion form leads to increased chemokine secretion and reduced osteoblast function.…”

Definition of human blood monocytes

“…Peters pointed out that monocytes not only function as dendritic cell precursors but, based on the induction of alkaline phosphatase, they may acquire features of osteoblast [19]. Hence, depending on the culture conditions, these cells exhibit a surprising plasticity.…”