T-lymphocytes are not necessary for particulate polyethylene-induced macrophage recruitment. Histologic studies of the rat tibia

The pathobiology and pathology of aseptic implant failure

Pathological assessment of periprosthetic tissues is important, not only for diagnosis, but also for understanding the pathobiology of implant failure. The host response to wear particle deposition in periprosthetic tissues is characterised by cell and tissue injury, and a reparative and inflammatory response in which there is an innate and adaptive immune response to the material components of implant wear. Physical and chemical characteristics of implant wear influence the nature of the response in periprosthetic tissues and account for the development of particular complications that lead to implant failure, such as osteolysis which leads to aseptic loosening, and soft-tissue necrosis/inflammation, which can result in pseudotumour formation. The innate response involves phagocytosis of implant-derived wear particles by macrophages; this is determined by pattern recognition receptors and results in expression of cytokines, chemokines and growth factors promoting inflammation and osteoclastogenesis; phagocytosed particles can also be cytotoxic and cause cell and tissue necrosis. The adaptive immune response to wear debris is characterised by the presence of lymphoid cells and most likely occurs as a result of a cell-mediated hypersensitivity reaction to cell and tissue components altered by interaction with the material components of particulate wear, particularly metal ions released from cobalt-chrome wear particles.Cite this article: Professor N. A. Athanasou. The pathobiology and pathology of aseptic implant failure. Bone Joint Res 2016;5:162-168. DOI: 10.1302/2046-3758.55.BJR-2016-0086.

Innate Immunity and Biomaterials at the Nexus: Friends or Foes

Biomaterial implants are an established part of medical practice, encompassing a broad range of devices that widely differ in function and structural composition. However, one common property amongst biomaterials is the induction of the foreign body response: an acute sterile inflammatory reaction which overlaps with tissue vascularisation and remodelling and ultimately fibrotic encapsulation of the biomaterial to prevent further interaction with host tissue. Severity and clinical manifestation of the biomaterial-induced foreign body response are different for each biomaterial, with cases of incompatibility often associated with loss of function. However, unravelling the mechanisms that progress to the formation of the fibrotic capsule highlights the tightly intertwined nature of immunological responses to a seemingly noncanonical “antigen.” In this review, we detail the pathways associated with the foreign body response and describe possible mechanisms of immune involvement that can be targeted. We also discuss methods of modulating the immune response by altering the physiochemical surface properties of the biomaterial prior to implantation. Developments in these areas are reliant on reproducible and effective animal models and may allow a “combined” immunomodulatory approach of adapting surface properties of biomaterials, as well as treating key immune pathways to ultimately reduce the negative consequences of biomaterial implantation.

Toll-like receptors-2 and 4 are overexpressed in an experimental model of particle-induced osteolysis

Aseptic loosening secondary to particle-associated periprosthetic osteolysis remains a major cause of failure of total joint replacements (TJR) in the mid- and long term. As sentinels of the innate immune system, macrophages are central to the recognition and initiation of the inflammatory cascade, which results in the activation of bone resorbing osteoclasts. Toll-like receptors (TLRs) are involved in the recognition of pathogen-associated molecular patterns and danger-associated molecular patterns. Experimentally, polymethylmethacrylate and polyethylene (PE) particles have been shown to activate macrophages via the TLR pathway. The specific TLRs involved in PE particle-induced osteolysis remain largely unknown. We hypothesized that TLR-2, -4, and -9 mediated responses play a critical role in the development of PE wear particle-induced osteolysis in the murine calvarium model. To test this hypothesis, we first demonstrated that PE particles caused observable osteolysis, visible by microCT and bone histomorphometry when the particles were applied to the calvarium of C57BL/6 mice. The number of TRAP positive osteoclasts was significantly greater in the PE-treated group when compared to the control group without particles. Finally, using immunohistochemistry, TLR-2 and TLR-4 were highly expressed in PE particle-induced osteolytic lesions, whereas TLR-9 was downregulated. TLR-2 and -4 may represent novel therapeutic targets for prevention of wear particle-induced osteolysis and accompanying TJR failure.

Do tissues from THA revision of highly crosslinked UHMWPE liners contain wear debris and associated inflammation?

BACKGROUND

Polyethylene wear debris is a major contributor to inflammation and the development of implant loosening, a leading cause of THA revisions. To reduce wear debris, highly crosslinked ultrahigh-molecular-weight polyethylene (UHMWPE) was introduced to improve wear properties of bearing surfaces. As highly crosslinked UHMWPE revision tissues are only now becoming available, it is possible to examine the presence and association of wear debris with inflammation in early implant loosening.

QUESTIONS/PURPOSES

We asked: (1) Does the presence of UHMWPE wear debris in THA revision tissues correlate with innate and/or adaptive immune cell numbers? (2) Does the immune cell response differ between conventional and highly crosslinked UHMWPE cohorts?

METHODS

We collected tissue samples from revision surgery of nine conventional and nine highly crosslinked UHMWPE liners. Polarized light microscopy was used to determine 0.5- to 2-μm UHMWPE particle number/mm2, and immunohistochemistry was performed to determine macrophage, T cell, and neutrophil number/mm2.

RESULTS

For the conventional cohort, correlations were observed between wear debris and the magnitude of individual patient macrophage (ρ=0.70) and T cell responses (ρ=0.71) and between numbers of macrophages and T cells (ρ=0.77) in periprosthetic tissues. In comparison, the highly crosslinked UHMWPE cohort showed a correlation between wear debris and the magnitude of macrophage responses (ρ=0.57) and between macrophage and T cell numbers (ρ=0.68). Although macrophages and T cells were present in both cohorts, the highly crosslinked UHMWPE cohort had lower numbers, which may be associated with shorter implantation times.

CONCLUSIONS

The presence of wear debris and inflammation in highly crosslinked UHMWPE revision tissues may contribute to early implant loosening.

Wear particles, periprosthetic osteolysis and the immune system

The immune system modulates many key biological processes in humans. However, the exact role of the immune system in particle-associated periprosthetic osteolysis is controversial. Human tissue retrieval studies, in vivo and in vitro experiments suggest that the immune response to polymer particles is non-specific and macrophage-mediated. Lymphocytes may modulate this response. However direct lymphocyte activation by polymer particle-protein complexes seems unlikely. However, metallic byproducts may complex with serum proteins and lead to a Type IV, lymphocyte-mediated immune reaction. In predisposed individuals, this reaction may rarely lead to persistent painful joint effusions, necessitating debridement and excision of the bearing surfaces of the prosthesis. In these patients, retrieved periprosthetic tissues exhibit histological evidence of perivascular lymphocytic cuffing. These findings are worrisome, given the fact that increasing numbers of metal-on-metal joint implants are being implanted in younger more active individuals worldwide.

The cellular and molecular biology of periprosthetic osteolysis

The generation of prosthetic implant wear after total joint arthroplasty is recognized as the major initiating event in development of periprosthetic osteolysis and aseptic loosening, the leading complication of this otherwise successful surgical procedure. We review current concepts of how wear debris causes osteolysis, and report ideas for prevention and treatment. Wear debris primarily targets macrophages and osteoclast precursor cells, although osteoblasts, fibroblasts, and lymphocytes also may be involved. Molecular responses include activation of MAP kinase pathways, transcription factors (including NFkappaB), and suppressors of cytokine signaling. This results in up-regulation of proinflammatory signaling and inhibition of the protective actions of antiosteoclastogenic cytokines such as interferon gamma. Strategies to reduce osteolysis by choosing bearing surface materials with reduced wear properties should be balanced by awareness that reducing particle size may increase biologic activity. There are no approved treatments for osteolysis despite the promise of therapeutic agents against proinflammatory mediators (such as tumor necrosis factor) and osteoclasts (bisphosphonates and molecules blocking receptor activator of NFkappaB ligand [RANKL] signaling) shown in animal models. Considerable efforts are underway to develop such therapies, to identify novel targets for therapeutic intervention, and to develop effective outcome measures.

The central role of wear debris in periprosthetic osteolysis

Periprosthetic osteolysis remains the leading complication of total hip arthroplasty, often resulting in aseptic loosening of the implant, and a requirement for revision surgery. Wear-generated particular debris is the main cause of initiating this destructive process. The purpose of this article is to review recent advances in our understanding of how wear debris causes osteolysis, and emergent strategies for the avoidance and treatment of this disease. The most important cellular target for wear debris is the macrophage, which responds to particle challenge in two distinct ways, both of which contribute to increased bone resorption. First, it is well known that wear debris activates proinflammatory signaling, which leads to increased osteoclast recruitment and activation. More recently, it has been established that wear also inhibits the protective actions of antiosteoclastogenic cytokines such as interferon gamma, thus promoting differentiation of macrophages to bone-resorbing osteoclasts. Osteoblasts, fibroblasts, and possibly lymphocytes may also be involved in responses to wear. At a molecular level, wear particles activate MAP kinase cascades, NFkappaB and other transcription factors, and induce expression of suppressors of cytokine signaling. Strategies to reduce osteolysis by choosing bearing surface materials with reduced wear properties (such as metal-on-metal) should be balanced by awareness that reducing particle size may increase biological activity. Finally, although therapeutic agents against proinflammatory mediators [such as tumor necrosis factor (TNF)] and osteoclasts (bisphosphonates and molecules blocking RANKL signaling) have shown promise in animal models, no approved treatments are yet available to osteolysis patients. Considerable efforts are underway to develop such therapies, and to identify novel targets for therapeutic intervention.

Effect of bisphosphonates on the stimulation of macrophages by alumina ceramic particles: a comparison with ultra-high-molecular-weight polyethylene

Wear particle-induced osteolysis and loosening is a critical process that limits the longevity of total hip arthroplasty. Despite their potential value in the management of aseptic loosening, little is known about the cellular response to bisphosphonates (BPs) in the presence of particulate debris. In the present study, we compared the effect of pamidronate and clodronate, two structurally different bisphosphonates, on the induction of TNF-alpha release by alumina ceramic (Al(2)O(3)) and ultra-high-molecular-weight-polyethylene (UHMWPE) particles. We also looked, by Trypan blue exclusion, at the viability of J774 mouse macrophages incubated with Al(2)O(3) and UHMWPE particles in combination with pamidronate or clodronate. Results showed that pamidronate and clodronate can inhibit UHMWPE particle-induced TNF-alpha release while they had no effect on Al(2)O(3)-stimulated TNF-alpha release. The co-incubation of pamidronate or clodronate and Al(2)O(3) had no effect on the induction by Al(2)O(3) of poly(ADP-ribose)polymerase (PARP) proteolysis and DNA fragmentation. On the other hand, UHMWPE particles had no effect on these apoptotic markers. However, the co-incubation of pamidronate or clodronate with UHMWPE particles led to the appearance of these markers of apoptosis. Al(2)O(3) and UHMWPE particles had no effect on macrophage cell death or the number of macrophages at the end of experiments. Co-incubation of UHMWPE particles with pamidronate and clodronate led to a significant increase in cell death. Interestingly, the number of macrophages co-incubated with particles and pamidronate or clodronate significantly decreased. In conclusion, our results suggest that the effect of BPs on particle-stimulated macrophages is, at least in part, particle composition dependent.

Polyethylene and titanium particles induce osteolysis by similar, lymphocyte-independent, mechanisms

Periprosthetic osteolysis is a major clinical problem that limits the long-term survival of total joint arthroplasties. Osteolysis is induced by implant-derived wear particles, primarily from the polyethylene bearing surfaces. This study examined two hypotheses. First, that similar mechanisms are responsible for osteolysis induced by polyethylene and titanium particles. Second, that lymphocytes do not play a major role in particle-induced osteolysis. To test these hypotheses, we used the murine calvarial model that we have previously used to examine titanium-induced osteolysis. Polyethylene particles rapidly induced osteolysis in the murine calvaria 5-7 days after implantation. The polyethylene-induced osteolysis was associated with large numbers of osteoclasts as well as the formation of a thick periosteal fibrous tissue layer with numerous macrophages containing phagocytosed polyethylene particles. Polyethylene-induced osteolysis was rapidly repaired and was undetectable by day 21 after implantation. Lymphocytes were noted in the fibrous layer of wild-type mice. However, the amount of osteolysis and cytokine production induced by polyethylene particles was not substantially affected by the lack of lymphocytes in Pfp/Rag2 double knock out mice. All of these findings are similar to our observations of osteolysis induced by titanium particles. These results provide strong support for both of our hypotheses: that similar mechanisms are responsible for osteolysis induced by polyethylene and titanium particles and that lymphocytes do not play a major role in particle-induced osteolysis.

Histologic reactions to particulate wear debris in different mesenchymal tissues: studies on the nonreplaced compartment from revised uni-knees

The interface between bone and artificial-joint implants consists of soft tissue. This tissue varies from fibrocartilage to loose fibrous tissue. Tissues that resemble those can be found in normal joints. Sixteen knees with unicompartmental knee prostheses, revised because of excessive wear of the tibial insert, were studied. Synovium, synovial fluid, cartilage, and bone from the nonreplaced compartment were studied with light microscopy. We found wear particles and reactions to those in all tissues except cartilage. In the subchondral bone, we found osteolytic-like processes undermining the cartilage peripherally. Our conclusion from these findings is that the histologic composition of the bone-implant interface might be an important factor regarding the reaction of the tissue to wear particles and, thus, component fixation.

The role of implant alignment on stability and particles on periprosthetic osteolysis?A rabbit model of implant failure

The study objective was to determine the tissue response to polyethylene and/or titanium particles and the role that these play in peri-prosthetic osteolysis in a rabbit model of implant failure. Twenty-two mature rabbits were used. Unilateral tibial arthroplasty was performed on all of them. The test animals received implants that were intentionally rotationally unstable with reference to the host tibia in order to create a model of failure. The test rabbits were divided into three groups. Group 1 consisted of seven rabbits in which only the carrier was implanted. Group 2 consisted of seven rabbits that received only polyethylene particles suspended in the carrier. Group 3 consisted of eight rabbits that received a mixture of polyethylene and titanium alloy particles suspended in the carrier. The rabbits were sacrificed at 6 months post surgery. The entire knee, together with the immediately surrounding soft tissue, was retrieved. The position of the implant in each rabbit was assessed with reference to its alignment to the tibia. The number of inflammatory, foreign-body reactive cells, the presence of neovascularization, edema, and necrosis in the periprosthetic zones were recorded and assessed in a qualitative and semiquantitative manner. Quantitative histomorphometry was used to determine the proportion of implant surface that interfaced with osseous or fibrous tissue. Also assessed was the thickness and maturity of the fibrous tissue and the endosteal remodeling activity in the peri-implant bone counting both osteoclastic and osteoblastic activity. The results showed that implanted particles and misalignment of the implants combined to produce peri-prosthetic bone resorption. Bone resorption was found to be proportional to the degree of misalignment. The animals that received combined polyethylene/titanium particles had a greater degree of foreign-body and inflammatory response with osteolysis than the other groups. The combination of bio-material particles (polyethylene and titanium alloy) produced a greater degree of bone resorption than the single biomaterial particles (polyethylene). The amount of bone resorption surrounding the implant was directly proportional to the degree of misalignment of the implant.

Effect of pamidronate on the stimulation of macrophage TNF-alpha release by ultra-high-molecular-weight polyethylene particles: a role for apoptosis

The demonstration that one of the mechanisms of action of bisphosphonates (BPs) is the induction of osteoclast and macrophage apoptosis, suggests a potent therapeutic role for the BPs and other apoptosis-modulating agents in the management of periprosthetic osteolysis. The purpose of this study was to improve our understanding of the basic underlying molecular events leading to the inhibitory effect of pamidronate on the macrophage response to ultra-high-molecular-weight polyethylene (UHMWPE) particles. Murine J774 macrophages were incubated for 0-72 h in the presence of UHMWPE particles and/or pamidronate. TNF-alpha release was measured by ELISA while poly(ADP-ribose)polymerase (PARP) expression was measured by Western blot. DNA was analyzed on agarose. The appearance of PARP fragment and the fragmentation of DNA were used as markers of apoptosis. We observed a dose-dependent response to UHMWPE particles with TNF-alpha release reaching 4, 10, and 19 times control with 10, 25, and 125 particles/macrophage, respectively. UHMWPE particles (25 particles/macrophage) stimulate TNF-alpha release by a factor of 10, 7, and 6 after 24, 48, and 72 h, respectively, indicating a rapid stimulating effect of UHMWPE particles on TNF-alpha release. Our results also showed that at 10 particles/macrophage, pamidronate inhibits UHMWPE-induced TNF-alpha release by 12%, 14%, and 23% respectively after 24, 48, and 72 h (p<0.05 vs. 24 and 48 h). With 25 particles/macrophage, the inhibition of TNF-alpha reached 9%, 12%, and 15% after 24, 48, and 72 h (p<0.05 vs. 24 h), respectively. There is no significant difference between the inhibition by pamidronate of TNF-alpha release induced by 125 particles/macrophages at 24, 48, and 72 h. When cells are pre-incubated for 48 h with pamidronate prior to addition of UHMWPE particles for 24 h, we observed an increased inhibition of TNF-alpha compared to the co-incubation protocol. The inhibiting effect of pamidronate reaches 56% when pre-incubated with macrophages prior to incubation with 10 particles of UHMWPE/macrophage (p<0.05 vs. co-incubation).Co-incubation of pamidronate with UHMWPE particles also led to the appearance of the proteolytic PARP fragment after 24 h incubation. We also demonstrated the stimulation of DNA fragmentation (DNA laddering) after 48-72 h with pamidronate. The proteolytic cleavage of PARP, an early event in the induction of apoptosis, precedes the inhibition of UHMWPE particle-induced TNF-alpha release by pamidronate whereas the fragmentation of DNA, a late apoptotic event, parallels this inhibition. Our results suggest the induction of macrophage apoptosis is associated with the inhibitory effect of pamidronate on TNF-alpha release. There is a need for the development of medical management of periprosthetic osteolysis. The demonstration that drugs such as pamidronate induce specific apoptosis-related pathways in macrophages contributes data for a rational approach in the treatment and/or prevention of periprosthetic osteolysis.

Differential apoptotic response of J774 macrophages to alumina and ultra-high-molecular-weight polyethylene particles

We recently identified apoptosis in in vitro wear particle-stimulated macrophages. The recent explosion of interest in apoptosis lies in the fact that it is under positive and negative regulation through evolutionary conserved biochemical pathways. It may also be possible to modulate macrophage apoptosis in the treatment of periprosthetic osteolysis. The purpose of this study was to compare the macrophage response to identically sized particles of alumina ceramic (Al2O3) and ultra-high-molecular-weight polyethylene (UHMWPE) in terms of TNF-alpha release and induction of apoptosis. J774 mouse macrophages were incubated for 0-24 h in the presence of Al2O3 and UHMWPE particles. TNF-alpha release was measured by ELISA; Poly(ADP-ribose)polymerase (PARP) and caspase-3 expression was analyzed by Western blot; DNA fragmentation (DNA laddering) was visualized on agarose gel containing ethidium bromide. Al2O3 particles induced TNF-alpha release after 4 h incubation with concentrations reaching 483 and 800 pg/ml after 24 h with 125 and 250 particles/macrophage, respectively (control = 161 pg/ml) (P < 0.05 vs. control). The same concentrations of UHMWPE particles induced a much larger and significant TNF-alpha release after only 1 h incubation, increasing up to 6250 pg/ml after 24 h (P < 0.05 vs. control). Western blot analysis demonstrated that the active caspase-3 fragment (17 kDa) and the proteolytic PARP fragment (85 kDa) were expressed after 2 h incubation with 125 and 250 Al2O3 particles/macrophage. The active caspase-3 and the PARP fragment had lower expression and appeared after a longer incubation time (8 h) with 125 and 250 UHMWPE particles/macrophage. Finally, DNA fragmentation (DNA laddering) was observed after 16 h with 125 and 250 particles of Al2O3 per macrophage whereas no laddering was induced by UHMWPE particles even after 24 h incubation. This study shows that although both Al2O3 and UHMWPE particles induce TNF-alpha release, this stimulation was much greater (8-10 times higher) with UHMWPE than Al2O3 (P < 0.05 vs. control). As well, the induction of apoptosis, as measured by activation of caspase-3, PARP cleavage and DNA laddering, is different for these two particles, being faster and more important with Al2O3 than UHMWPE. We hypothesize that the ability of Al2O3 to induce macrophage apoptosis may explain the lower TNF-alpha release observed with these particles and explain the differences seen in osteolysis patterns of ceramic-ceramic (CC) vs. metal-polyethylene (Mpe) articulations. In conclusion, apoptosis may be a major internal mechanism to decrease macrophage activity and may be a desired therapeutic endpoint. The identification of an apoptosis-related pathway in the macrophage response to ceramic particles provides crucial data for a rational approach in the treatment and/or prevention of periprosthetic osteolysis.

No lymphokines in T-cells around loosened hip prostheses

Research results have been contradictory about the role of lymphocytes and immune response in aseptic loosening of total hip replacement (THR). Conclusive evidence is still lacking in spite of extensive in vivo and in vitro studies. Our study was designed to check whether T-cells were activated and if they produced lymphokines in synovial membrane-like interface tissue around loosened THRs. Tissue sections were stabilized and permeabilized to allow the cytokine-specific antibodies to penetrate through the cell membrane and the membranes of intracellular organelles. This technique, combined with computer-assisted image analysis, permits the detection and quantitation of lymphokine-producing cells. We found that the number of T-cells was low, and none of the T-cells was activated, as shown by the absence of interleukin-2 receptor (IL-2R) immunoreactivity. There was no cell producing lymphokines, such as interleukin-2 (IL-2), interferon-gamma (IFN-gamma), and tumor necrosis factor-beta (TNF-beta). Our results suggest that T-cell-mediated immune response is not actively involved in aseptic loosening of THR.

Histological and compositional evaluations of three types of calcium phosphate cements when implanted in subcutaneous tissue immediately after mixing

To evaluate the soft tissue response of calcium phosphate cement (CPC), consisting of an equimolar mixture of tetracalcium phosphate (TTCP) and dicalcium phosphate anhydrous (DCPA) under conditions close to those encountered in actual surgical procedures, we implanted three types of CPC [conventional CPC (c-CPC), fast-setting CPC (FSCPC), and antiwashout type FSCPC (aw-FSCPC; formerly called nondecay type FSCPC or nd-FSCPC)] subcutaneously in the abdomens of rats immediately (1 min) after mixing. At 1 week after surgery, histological examination and compositional analysis were performed using light microscopy and powder X-ray diffraction (XRD), respectively. The implanted c-CPC was crumbled completely, whereas FSCPC and aw-FSCPC retained their shape. Large vesicles containing copious inflammatory effusion were subcutaneously formed around the c-CPC. Histologically, many foreign-body giant cells were collected around the c-CPC, and moderate inflammatory cell infiltration was observed at 1 week after surgery. In contrast, the FSCPC and aw-FSCPC were covered with a thin layer of granulation tissue that included few giant cells and presented slight inflammatory cell infiltration, and no effusion was observed. The XRD analysis of the c-CPC revealed the presence of some unreacted DCPA even 1 week after implantation, whereas almost no DCPA was found in the FSCPC or aw-FSCPC. In conclusion, it was found that CPC does not always show excellent tissue response. When c-CPC is implanted subcutaneously in rats immediately after mixing, it fails to set and causes a severe inflammatory response. Therefore, the type of CPC should be chosen according to the clinical particulars. CPC should be used in a manner that assures its setting reaction. We recommend the use of FSCPC and aw-FSCPC for surgical applications, such as orthopedics, plastic and reconstructive surgery, and oral and maxillofacial surgery, where the cement might otherwise crumble due to the pressure before setting.

Interferon-gamma exacerbates polymethylmethacrylate particle-induced interleukin-6 release by human monocyte/macrophages in vitro

Periprosthetic membranes commonly observed at sites of total joint implant loosening exhibit abundant macrophages and particulate debris. Macrophages phagocytose orthopedic debris and release the pro-inflammatory mediators interleukin-1, interleukin-6, tumor necrosis factor-alpha, and prostaglandin E2. In addition, other immunologic agents, such as interferon-gamma, are present in tissues harvested from the bone-implant interface of failed orthopedic implants. The present study examined the effects of interferon-gamma on polymethylmethacrylate (PMMA) particle-challenged monocyte/macrophages in vitro. The effects of interferon-gamma were determined by measuring interleukin-6 and tumor necrosis factor-alpha release by primary human monocyte/macrophages following exposure to PMMA particles. Exposure of the monocyte/macrophages to PMMA particles resulted in a dose-dependent release of interleukin-6 and tumor necrosis factor-alpha at 48 h. The interleukin-6 release in response to PMMA particle challenge was stimulated by 76% and 127% in the presence of 1.0 and 10.0 ng/mL of interferon-gamma, respectively. Interferon-gamma challenge alone did not alter interleukin-6 release relative to controls. In contrast to interleukin-6, interferon-gamma challenge stimulated tumor necrosis factor-alpha release in a dose-dependent manner. In the presence of particles, addition of 1.0 and 10.0 ng/mL of interferon-gamma resulted in 17% and 171% increases in the levels of tumor necrosis factor-alpha release, respectively, relative to cultures challenged solely with particles. Blocking antibody to IFN-gamma inhibited the effect of IFN-gamma on particle-induced interleukin-6 and tumor necrosis factor-alpha release. The data presented in this study demonstrate that the immunologic modulator interferon-gamma exacerbates monocyte/macrophage release of the pro-inflammatory cytokines interleukin-6 and tumor necrosis factor-alpha in response to PMMA particle challenge in vitro.

Soft tissue response to polytetrafluoroethylene and silicone rubber in humans: morphological and immunohistochemical observations

The objective of this study was by morphological and immunohistochemical means to investigate the cellular tissue response to the alloplastic materials polytetrafluoroethylene (PTFE polymer), and soft and hard silicone rubber over time. In seven healthy volunteers implants made of Proplast-Teflon, and soft and hard silicone were inserted subcutaneously in unloaded areas in the iliac crest region. After 1, 2, 4, 12, and 26 weeks, respectively, the implants with surrounding soft tissue were removed en bloc for histological and immunohistochemical examination using a panel of antibodies to various leukocyte markers. The tissue reaction to the various alloplastic materials varied greatly with the focus on macrophage and giant cell reactions and eventual formation of a peri-implant fibrous capsule. The most extensive changes developed next to porous Proplast, both with respect to degree of changes and endurance of tissue reaction. Less intense reactions were seen, in decreasing order, to soft silicone, Teflon, and hard silicone. The study gave no clues to a toxic, allergic, or traditional immunological pathogenesis of the tissue reaction induced by the test materials.

Loosening and osteolysis of cemented joint arthroplasties. A biologic spectrum

The purpose of this study was to characterize the cell types (using immunohistochemistry) and cytokine expression (using in situ hybridization) of tissues surrounding well fixed and loose cemented prostheses undergoing revision. Clinical and radiographic data were gathered prospectively for a series of cemented total joint replacements undergoing revision. Three groups were identified: (1) loose implants with osteolysis (10 specimens), (2) loose implants without osteolysis (11 specimens), and (3) well fixed implants (7 specimens). At surgery, a specimen was harvested from the bone cement interface. Immunohistochemical staining was performed using monoclonal antibodies to identify macrophages and lymphocyte subgroups. Human antisense probes were selected to identify the mRNA for specific cytokines using in situ hybridization. The percentage of positively staining cells was determined for each antibody or probe using a grid counting technique. Tissues from loose cemented prostheses with osteolysis contained significantly greater numbers of macrophages and T lymphocytes compared with tissues from loose and well fixed cemented prostheses without osteolysis. The number of interleukin-1 and interleukin-6 positive cells was highest in specimens with osteolysis and lowest in specimens from well fixed prostheses. These cytokines modulate the growth and differentiation of cells in the immune system and the monocyte and macrophage system and mediate the remodeling of bone and mesenchymal tissues. Specific cell populations and cytokine profiles appear to be involved in periprosthetic osteolysis; this information may be useful in planning strategies for prevention and treatment.

Effects of polyethylene on macrophages

A system was developed to expose macrophages to polyethylene in vitro. Exposure of macrophages to these particles in isolation led to the release of tumor necrosis factor alpha and prostaglandin E2. Exposure of macrophages in co-culture with osteoblasts to polyethylene particles increased the release of prostaglandin E2 and also led to the release of interleukin-6. Incubation of radiolabelled calvariae with conditioned medium from macrophages exposed to polyethylene particles alone or to particles in co-culture with osteoblasts led to bone resorption reflected by release of 45Ca. Incubation with pamidronate was effective in inhibiting resorption stimulated by conditioned medium from macrophages exposed to these particles alone or in co-culture with osteoblasts. This demonstrates that pamidronate, or other bisphosphonates, may be effective in inhibiting bone resorption at the implant/bone interface in association with the macrophage response to particulate polyethylene. Further investigation into the possible use of pamidronate or other bis-phosphonates in the treatment of aseptic loosening is warranted.

Polyethylene particles stimulate monocyte chemotactic and activating factor production in synovial mononuclear cells in vivo. An immunohistochemical study in rabbits

We report that polyethylene particles can activate mononuclear cells within the joint to produce the monocyte chemotactic and activating factor (MCAF) and to a lesser degree interleukin 8 (IL-8) as judged by immunohistological staining. Polyethylene particles suspended in hyaluronic acid were injected weekly for 12 weeks into the right knee joint of New Zealand white rabbits. The average size of the particles was 7 (3-12) microns in diameter. The left knee joint was injected with hyaluronic acid as the control. The animals were killed after 13 weeks. On the control side, the synovial membrane was histologically normal, without signs of inflammation. In the knees that were injected with polyethylene particles, histological analysis showed a weak inflammatory response, consisting of mononuclear cells, multi-nucleated giant cells and polyethylene particles. In the vicinity of the particles, the presence of mononuclear cells that were highly positive for MCAF was noted, whereas IL-8 was present in endothelial cells and in the lining layer, but not in cells in the vicinity of polyethylene particles, suggesting that polyethylene particles are able to activate cytokine metabolism in a differentiated way in the synovial monocytes.