The role of the TH1 and TH2 immune responses in loosening and osteolysis of cemented total hip replacements

Prevention and treatment of peri-implant fibrosis by functionally inhibiting skeletal cells expressing the leptin receptor

The cellular and molecular mediators of peri-implant fibrosis-a most common reason for implant failure and for surgical revision after the replacement of a prosthetic joint-remain unclear. Here we show that peri-implant fibrotic tissue in mice and humans is largely composed of a specific population of skeletal cells expressing the leptin receptor (LEPR) and that these cells are necessary and sufficient to generate and maintain peri-implant fibrotic tissue. In a mouse model of tibial implantation and osseointegration that mimics partial knee arthroplasty, genetic ablation of LEPR+ cells prevented peri-implant fibrosis and the implantation of LEPR+ cells from peri-implant fibrotic tissue was sufficient to induce fibrosis in secondary hosts. Conditional deletion of the adhesion G-protein-coupled receptor F5 (ADGRF5) in LEPR+ cells attenuated peri-implant fibrosis while augmenting peri-implant bone formation, and ADGRF5 inhibition by the intra-articular or systemic administration of neutralizing anti-ADGRF5 in the mice prevented and reversed peri-implant fibrosis. Pharmaceutical agents that inhibit the ADGRF5 pathway in LEPR+ cells may be used to prevent and treat peri-implant fibrosis.

Nano wear particles and the periprosthetic microenvironment in aseptic loosening induced osteolysis following joint arthroplasty

Joint arthroplasty is an option for end-stage septic arthritis due to joint infection after effective control of infection. However, complications such as osteolysis and aseptic loosening can arise afterwards due to wear and tear caused by high joint activity after surgery, necessitating joint revision. Some studies on tissue pathology after prosthesis implantation have identified various cell populations involved in the process. However, these studies have often overlooked the complexity of the altered periprosthetic microenvironment, especially the role of nano wear particles in the etiology of osteolysis and aseptic loosening. To address this gap, we propose the concept of the "prosthetic microenvironment". In this perspective, we first summarize the histological changes in the periprosthetic tissue from prosthetic implantation to aseptic loosening, then analyze the cellular components in the periprosthetic microenvironment post prosthetic implantation. We further elucidate the interactions among cells within periprosthetic tissues, and display the impact of wear particles on the disturbed periprosthetic microenvironments. Moreover, we explore the origins of disease states arising from imbalances in the homeostasis of the periprosthetic microenvironment. The aim of this review is to summarize the role of relevant factors in the microenvironment of the periprosthetic tissues, in an attempt to contribute to the development of innovative treatments to manage this common complication of joint replacement surgery.

Do Battlefield Injury-acquired Indwelling Metal Fragments Induce Metal Immunogenicity?

BACKGROUND

A battlefield-related injury results in increased local and systemic innate immune inflammatory responses, resulting in wound-specific complications and an increased incidence of osteoarthritis. However, little is known about whether severe injuries affect long-term systemic homeostasis, for example, immune function. Moreover, it also remains unknown whether battlefield-acquired metal fragments retained over the long term result in residual systemic effects such as altered immune reactivity to metals.

QUESTIONS/PURPOSES

Does a retained metal fragment from a battlefield injury contribute to increased (1) adaptive metal-specific immune responses, (2) systemically elevated metal ion serum levels, and (3) serum immunoglobulin levels compared with combat injuries that did not result in a retained metal fragment?

METHODS

In this pilot study, we analyzed metal-immunogenicity in injured military personnel and noninjured control participants using lymphocyte transformation testing (LTT, lymphocyte proliferation responses to cobalt, chromium and nickel challenge at 0.001, 0.01 and 0.1-mM concentrations in triplicate for each participant), serum metal ion analysis (ICP-mass spectroscopy), and serum immunoglobulin analysis (IgE, IgG, IgA, and IgM ). Military personnel with a battlefield-sustained injury self-recruited without any exclusion for sex, age, degree of injury. Those with battlefield injury resulting in retained metal fragments (INJ-FRAG, n = 20 male, mean time since injury ± SD was 12 ± 10 years) were compared with those with a battlefield injury but without retained metal fragments (INJ-NO-FRAG, n = 12 male, mean time since injury ± SD was 13 ± 12 years). A control group comprised of male noninjured participants was used to compare measured immunogenicity metrics (n = 11, males were selected to match battlefield injury group demographics).

RESULTS

Military participants with sustained metal fragments had increased levels of metal-induced lymphocyte responses. The lymphocyte stimulation index among military participants with metal fragments was higher than in those with nonretained metal fragments (stimulation index = 4.2 ± 6.0 versus stimulation index = 2.1 ± 1.2 (mean difference 2.1 ± 1.4 [95% confidence interval 5.1 to 0.8]; p = 0.07) and an average stimulation index = 2 ± 1 in noninjured controls. Four of 20 participants injured with retained fragments had a lymphocyte proliferation index greater than 2 to cobalt compared with 0 in the group without a retained metal fragment or 0 in the control participants. However, with the numbers available, military personnel with retained metal fragments did not have higher serum metal ion levels than military participants without retained metal fragment-related injuries or control participants. Military personnel with retained metal fragments had lower serum immunoglobulin levels (IgG, IgA, and IgM) than military personnel without retained metal fragments and noninjured controls, except for IgE. Individuals who were metal-reactive positive (that is, a stimulation index > 2) with retained metal fragments had higher median IgE serum levels than participants who metal-reactive with nonmetal injuries (1198 ± 383 IU/mL versus 171 ± 67 IU/mL, mean difference 1027 ± 477 IU/mL [95% CI 2029 to 25]; p = 0.02).

CONCLUSIONS

We found that males with retained metal fragments after a battlefield-related injury had altered adaptive immune responses compared with battlefield-injured military personnel without indwelling metal fragments. Military participants with a retained metal fragment had an increased proportion of group members and increased average lymphocyte reactivity to common implant metals such as nickel and cobalt. Further studies are needed to determine a causal association between exposure to amounts of retained metal fragments, type of injury, personnel demographics and general immune function/reactivity that may affect personal health or future metal implant performance.

LEVEL OF EVIDENCE

Level IV, therapeutic study.

[Mid- and long-term effectiveness of total hip arthroplasty with Ribbed femoral stem prosthesis in 354 cases]

Objective

To evaluate the mid- and long-term effectiveness of total hip arthroplasty (THA) with Ribbed femoral stem prosthesis.

Methods

A clinical data of 354 patients (384 hips) with hip disease who underwent THA with Ribbed femoral stem prostheses between October 2006 and May 2016 was retrospectively analyzed. There were 171 males and 183 females, with an average age of 53.4 years (range, 20-82 years). There were 324 cases of single hip and 30 cases of bilateral hips. The cause of THA included the avascular necrosis of the femoral head in 151 cases (159 hips), hip osteoarthritis in 134 cases (136 hips), rheumatoid arthritis in 43 cases (43 hips), ankylosing spondylitis in 20 cases (40 hips), and trauma in 6 cases (6 hips). The Harris score of total 354 patients before operation was 42.34±8.89. Harris scores were used to evaluate hip function after operation. X-ray films were used to determine the length of the lower limb, the radiolucent line on the femur side, the stability of the prosthesis, and the occurrence of stress shielding.

Results

The incisions healed by first intention. All patients were followed up 2-11 years with an average of 7.4 years. The Harris score at last follow-up was 80.52±7.61, which significantly increased when compared with preoperative score ( t=134.804, P=0.000). Two cases (2 hips) of prosthetic infections, 3 cases (3 hips) of prothesis loosening, and 4 cases (4 hips) of periprosthetic fractures, and 48 cases (48 hips) of mild to moderate thigh pain occurred after operation. X-ray films showed 76 cases (78 hips) with radiolucent lines on the femur side and stress shielding. According to the Engh's method, there were 364 hips of bone ingrowth, 15 hips of fibrosis ingrowth, and 5 hips of prosthesis instability. The femoral stem subsidence occurred in 25 cases (25 hips), and the difference in leg length discrepancy was more than 10 mm in 5 patients.

Conclusion

THA with Ribbed femoral stem prosthesis can achieve satisfactory effectiveness with good initial stability and rapid bone growth. The incidence of stress shielding is relatively high, but the stress shielding has no significant impact on the mid- and long-term survival rate and effectiveness of femoral prosthesis.

Cytokine Profile in Patients with Aseptic Loosening of Total Hip Replacements and Its Relation to Metal Release and Metal Allergy

Metal release from total hip replacements (THRs) is associated with aseptic loosening (AL). It has been proposed that the underlying immunological response is caused by a delayed type IV hypersensitivity-like reaction to metals, i.e., metal allergy. The purpose of this study was to investigate the immunological response in patients with AL in relation to metal release and the prevalence of metal allergy. THR patients undergoing revision surgery due to AL or mechanical implant failures were included in the study along with a control group consisting of primary THR patients. Comprehensive cytokine analyses were performed on serum and periimplant tissue samples along with metal analysis using inductive coupled plasma mass spectrometry (ICP-MS). Patient patch testing was done with a series of metals related to orthopedic implant. A distinct cytokine profile was found in the periimplant tissue of patients with AL. Significantly increased levels of the proinflammatory cytokines IL-1β, IL-2, IL-8, IFN-γ and TNF-α, but also the anti-inflammatory IL-10 were detected. A general increase of metal concentrations in the periimplant tissue was observed in both revision groups, while Cr was significantly increased in patient serum with AL. No difference in the prevalence of metal sensitivity was established by patch testing. Increased levels of IL-1β, IL-8, and TNF-α point to an innate immune response. However, the presence of IL-2 and IFN-γ indicates additional involvement of T cell-mediated response in patients with AL, although this could not be detected by patch testing.

The Inflammatory Effects of Breast Implant Particulate Shedding: Comparison With Orthopedic Implants

Currently, there is a dearth of information regarding the degree of particle shedding from breast implants (BIs) and what are the general biological consequences of BI debris. Thus, it is unclear to what degree BI debris compromises the long-term biological performance of BIs. For orthopedic implants, it is well established that the severity of biological reactivity to implant debris governs long-term clinical performance. Orthopedic implant particulate debris is generally in the range of 0.01 to 100 μm in diameter. Implant debris-induced bioreactivity/inflammation is mostly a peri-implant phenomenon caused by local innate immune cells (eg, macrophages) that produce proinflammatory cytokines such as tumor necrosis factor-α, interleukin-1β, interleukin-6, and prostaglandin 2 (PGE2). In orthopedics, there have been few systemic concerns associated with polymeric implant debris (like silicone) other than documented dissemination to remote organs (eg, liver, spleen, etc.) with no known associated pathogenicity. This is not true of metal implant debris where normal (well-functioning) implants can induce systemic reactions such as delayed type hypersensitivity. Diagnostic analysis of orthopedic tissues has focused on innate (macrophage mediated) and adaptive (lymphocyte-mediated hypersensitivity) immune responses. Orthopedic implant debris-associated lymphocyte cancers have not been reported in over 40 years of orthopedic literature. Adaptive immune responses such as hypersensitivity reactions to orthopedic implant debris have been dominated by certain implant types that produce specific kinds of debris (eg, metal-on-metal total joint prostheses). Orthopedic hypersensitivity responses and atypical BI bioreactivity such as BI-associated anaplastic large cell lymphoma share crossover markers for diagnosis. Differentiating normal innate immune reactivity to particles from anaplastic large cell lymphoma reactions from delayed type hypersensitivity reactions to BI-associated implant debris remains unclear but vital to patients and surgeons.

Titanium Ions Promote Exogenous Calcium-Dependent Calcium Influx in Activated Jurkat T Cells: A Possible Mechanism to Explain Its Immunostimulatory Properties

Titanium and its alloys have been widely used in dental and orthopedic implants. Owing to the biotribocorrosion behavior of implants in simulated oral environment, Ti(IV) ions could be released into surrounding tissues. Current studies have found that Ti(IV) ions could affect the biological activities of immune cells in adjacent tissues and subsequently jeopardize the long-term performance of implant prostheses. However, the potential mechanism underlying its immunomodulatory properties remains unclear. Calcium signaling has been confirmed to be involved in regulation of lymphocyte immune function. Therefore, we hypothesize that Ti(IV) ions modulated T cell function through the change of intracellular calcium concentrations. This study is aimed at exploring the role of intracellular calcium responses in the modulatory effect of Ti(IV) ions on unactivated and phytohemagglutinin-activated Jurkat T cells. Here, we confirmed that Ti(IV) ions within a certain concentration range induced CD69 expression on both unactivated and activated T cells in our study. Additionally, the combined stimulation with Ti(IV) ions and PHA increased expression of IL-1β, TNF-α, and RANKL. Furthermore, we found that treatment with Ti(IV) induced a transitory increase in the levels of [Ca²⁺]_i in activated Jurkat cells, dependent on the presence of exogenous calcium. Treatment with different doses of Ti(IV) for 24 h significantly increased the levels of [Ca²⁺]_i in the activated Jurkat cells in a dose-dependent manner, but had little effect in the unactivated cells. Treatment with Ti(IV) did not significantly affect the PLCγ1 activation and inositol-1,4,5-trisphosphate (IP₃) secretion in Jurkat cells. Taken together, these data indicated that Ti(IV) enhanced calcium influx during the T cell activation, independent of IP₃-mediated intracellular calcium release. Our work provides insights into the mechanism involved in the regulation of lymphocyte behaviors under the effect of Ti(IV) ions, which may help to develop therapeutic strategies for dental implant failures.

Preferential CD8 rather than CD4 T-cell response to wear particles of polyether-ether-ketone and highly cross-linked polyethylene

The efficacy of polyether-ether-ketone (PEEK) as a bearing material in knee components, a potential alternative to the currently used highly cross-linked polyethylene (HXLPE), has attracted a lot of attention recently. This study aimed to systematically assess the effect of particulate wear debris on CD4 and CD8 T-cell responses. HXLPE and PEEK particles (96% less than 5 μm) were generated by custom cryo-milling and pulverization in liquid nitrogen, and then incubated with blood collected from 25 donors. The phenotypes of the T-cells were systematically analyzed by immunostaining and flow cytometry. For the in vivo study, 0.1 mL of each particle suspension (about 1.0 × 10⁸ wear particles) was injected into murine knee joints; the synovium and spleen were collected one week later for histological examination and immunofluorescence staining. PEEK and HXLPE particles did not induce CD4+ T-cell responses; however, CD8+ T-cells might be involved in mediating particle-induced reactions. The T-cell and inflammatory responses induced by PEEK and HXLPE particles were comparable. Further investigations into the frictional properties of materials should be performed to expand on our results.

Enriching the understanding of the effects of the particles on the adaptive immune response.

Effects of wear particles of polyether-ether-ketone and cobalt-chromium-molybdenum on CD4- and CD8-T-cell responses

T-cells, second only to macrophages, are often considered as the potential cells involved in debris-related failure of arthroplasty. Here, we assessed the effects of particulate wear debris on T-cells and inflammatory reactions. Blood samples from 25 donors were incubated with polyether-ether-ketone (PEEK) and cobalt-chromium-molybdenum (CoCrMo) particles generated by custom cryo-milling and pulverization. The T-cell phenotypes were assessed using immunostaining and flow cytometry. For the in vivo study, 0.1 mL of each particle suspension (approximately 1.0 × 10⁸ wear particles) was injected into murine knee joints; the synovium and spleen were collected one week after the operation for histological examination and immunofluorescence staining. The T-cell responses observed included low-level activation of Th1, Th2, Th17, and CD8+ pathways after 72 h of co-culture of the particles with peripheral blood mononuclear cells. Obvious CD8+ T-cell responses were observed in local synovium and peripheral spleen, with higher inflammatory cytokine expression in the CoCrMo group. Relatively minor cytotoxic and immunological reactions were observed in vitro, with PEEK and CoCrMo particle-induced immune responses being primarily mediated by CD8+ T-cells, rather than CD4+ T-cells, in vivo. Overall, PEEK wear particles induced fewer inflammatory reactions than CoCrMo particles. This study verified that PEEK was suitable as a potential alternative for metals in total knee replacements in terms of the immunological reaction to PEEK particles, and shed light on the effects of wear particles from polymer and metal-based implants on immune responses.

How has the introduction of new bearing surfaces altered the biological reactions to byproducts of wear and modularity?

BACKGROUND

Biological responses to wear debris were largely elucidated in studies focused on conventional ultrahigh-molecular-weight polyethylene (UHMWPE) and some investigations of polymethymethacrylate cement and orthopaedic metals. However, newer bearing couples, in particular metal-on-metal but also ceramic-on-ceramic bearings, may induce different biological reactions.

QUESTIONS/PURPOSES

Does wear debris from the newer bearing surfaces result in different biological responses compared with the known responses observed with conventional metal-on-UHMWPE bearings?

METHODS

A Medline search of articles published after 1996 supplemented by a hand search of reference lists of included studies and relevant conference proceedings was conducted to identify the biological responses to orthopaedic wear debris with a focus on biological responses to wear generated from metal-on-highly crosslinked polyethylene, metal-on-metal, ceramic-on-ceramic, and ceramic-on-polyethylene bearings. Articles were selected using criteria designed to identify reports of wear debris particles and biological responses contributing to prosthesis failure. Case reports and articles focused on either clinical outcomes or tribology were excluded. A total of 83 papers met the criteria and were reviewed in detail.

RESULTS

Biological response to conventional UHMWPE is regulated by the innate immune response. It is clear that the physical properties of debris (size, shape, surface topography) influence biological responses in addition to the chemical composition of the biomaterials. Highly crosslinked UHMWPE particles have the potential to alter, rather than eliminate, the biological response to conventional UHMWPE. Metal wear debris can generate elevated plasma levels of cobalt and chromium ions. These entities can provoke responses that extend to the elicitation of an acquired immune response. Wear generated from ceramic devices is significantly reduced in volume and may provide the impression of an "inert" response, but clinically relevant biological reactions do occur, including granulomatous responses in periprosthetic tissues.

CONCLUSIONS

The material composition of the device, the physical form of the debris, and disease pathophysiology contribute to complex interactions that determine the outcome to all wear debris. Metal debris does appear to increase the complexity of the biological response with the addition of immunological responses (and possibly direct cellular cytotoxicity) to the inflammatory reaction provoked by wear debris in some patients. However, the introduction of highly crosslinked polyethylene and ceramic bearing surfaces shows promising signs of reducing key biological mechanisms in osteolysis.

Characterization of macrophage polarizing cytokines in the aseptic loosening of total hip replacements

Aseptic loosening of hip replacements is driven by the macrophage reaction to wear particles. The extent of particle-induced macrophage activation is dependent on the state of macrophage polarization, which is dictated by the local cytokine microenvironment. The aim of the study was to characterize cytokine microenvironment surrounding failed, loose hip replacements with an emphasis on identification of cytokines that regulate macrophage polarization. Using qRT-PCR, the expression of interferon gamma (IFN-γ), interleukin-4 (IL-4), granulocyte-macrophage colony-stimulating factor (GM-CSF), IL-13, and IL-17A was low and similar to the expression in control synovial tissues of patients undergoing primary hip replacement. Using immunostaining, no definite source of IFN-γ or IL-4 could be identified. IL-17A positive cells, identified as mast cells by double staining, were detected but their number was significantly reduced in interface tissues compared to the controls. Significant up-regulation of IL-10, M-CSF, IL-8, CCL2-4, CXCL9-10, CCL22, TRAP, cathepsin K, and down regulation of OPG was seen in the interface tissues, while expression of TNF-α, IL-1β, and CD206 were similar between the conditions. It is concluded that at the time of the revision surgery the peri-implant macrophage phenotype has both M1 and M2 characteristics and that the phenotype is regulated by other local and systemic factors than traditional macrophage polarizing cytokines.

Contributions of human tissue analysis to understanding the mechanisms of loosening and osteolysis in total hip replacement

Aseptic loosening and osteolysis are the most frequent late complications of total hip arthroplasty (THA) leading to revision of the prosthesis. This review aims to demonstrate how histopathological studies contribute to our understanding of the mechanisms of aseptic loosening/osteolysis development. Only studies analysing periprosthetic tissues retrieved from failed implants in humans were included. Data from 101 studies (5532 patients with failure of THA implants) published in English or German between 1974 and 2013 were included. "Control" samples were reported in 45 of the 101 studies. The most frequently examined tissues were the bone-implant interface membrane and pseudosynovial tissues. Histopathological studies contribute importantly to determination of key cell populations underlying the biological mechanisms of aseptic loosening and osteolysis. The studies demonstrated the key molecules of the host response at the protein level (chemokines, cytokines, nitric oxide metabolites, metalloproteinases). However, these studies also have important limitations. Tissues harvested at revision surgery reflect specifically end-stage failure and may not adequately reveal the evolution of pathophysiological events that lead to prosthetic loosening and osteolysis. One possible solution is to examine tissues harvested from stable total hip arthroplasties that have been revised at various time periods due to dislocation or periprosthetic fracture in multicenter studies.

Evidence for active antigen presentation by monocyte/macrophages in response to stimulation with particles: the expression of NFκB transcription factors and costimulatory molecules

BACKGROUND

The macrophage and lymphocyte response to wear debris contributes to the failure of some joint replacements. Costimulatory molecule expression by particle-containing macrophages is an evidence for antigen presentation. The NFκB transcription factors are regulators of costimulatory molecules and are present in tissue near failed joint prostheses. The tissue localisation of NFκB and the expression of these factors and costimulatory molecules by U937 cells stimulated with nano- and microparticles are reported, together with the effects of an NFκB inhibitor (sc514).

MATERIALS AND METHODS

The tissue localisation of RelA, RelB, c-rel, p50, p52 and NF-IL6 was examined by immunohistochemistry in samples from 15 patients with failure of metal against polyethylene total hip replacements. The expression of these NFκB factors by U937 cells stimulated with microparticles (CoCr, diamond) and nanoparticles (diamond) was examined by quantified RT-PCR. Lipopolysaccharide provided positive controls while negative controls had no additions to culture. Inhibition of NFκB activity by sc-514 was studied. The expression of costimulatory molecules (CD80, CD86 and HLA-DR) was evaluated in parallel cell culture studies by tricolour flow cytometry.

RESULTS AND DISCUSSION

Immunohistochemistry of tissue showed the highest expression for NF-IL6 (32.56 ± 11.61 per cent), RelA (33.66 ± 9.98 per cent) and p52 (32.07 ± 12.90 per cent), then RelB (22.63 ± 7.49 per cent), c-rel (14.07 ± 6.72 per cent) and p50 (13.07 ± 5.99 per cent). NF-IL6 was localised to macrophages, RelB to RFD1+ dendritic cells. U937 cells showed an increased expression of all NFκB factors (p < 0.01) in response to CoCr and diamond microparticles. Only RelA and c-rel (p < 0.01) were increased by one diamond nanoparticle and p52 and c-rel (p < 0.01) by another nanoparticulate diamond. Inhibition by sc-514 of RelA, c-rel and p50 expression occurred with all four particles, p52 was decreased for all diamond particles (but not CoCr) and RelB was not inhibited with any of the particles. CD86 and HLA-DR expression were upregulated by microparticles (CoCr, diamond) (p ≪ 0.01) with lower levels (significant) of these molecules found with diamond nanoparticles. CD80 expression was much less than CD86 and HLA-DR. Costimulatory molecule expression in the bone-implant interface indicates antigen presentation by macrophages. Functional studies with U937 monocytes show the same molecules expressed on exposure to micro- and nanoparticles. Highest values occur with CoCr while the smallest diamond nanoparticles are the least stimulatory. NFκB expression gives an insight into the immunogenic potential of the different particles.

Asymptomatic prospective and retrospective cohorts with metal-on-metal hip arthroplasty indicate acquired lymphocyte reactivity varies with metal ion levels on a group basis

Some tissues from metal-on-metal (MoM) hip arthroplasty revisions have shown evidence of adaptive-immune reactivity (i.e., excessive peri-implant lymphocyte infiltration/activation). We hypothesized that, prior to symptoms, some people with MoM hip arthroplasty will develop quantifiable metal-induced lymphocyte reactivity responses related to peripheral metal ion levels. We tested three cohorts (Group 1: n = 21 prospective longitudinal MoM hip arthroplasty; Group 2: n = 17 retrospective MoM hip arthroplasty; and Group 3: n = 20 controls without implants). We compared implant position, metal-ion release, and immuno-reactivity. MoM cohorts had elevated (p < 0.01) amounts of serum Co and Cr compared to controls as early as 3 months post-op (Group 1:1.2 ppb Co, 1.5 ppb Cr; Group 2: 3.4 ppb Co, 5.4 ppb Cr; Group 3: 0.01 ppb Co, 0.1 ppb Cr). However, only after 1-4 years post-op did 56% of Group 1 develop metal-reactivity (vs. 5% pre-op, metal-LTT, SI > 2), compared with 76% of Group 2, and 15% of Group 3 controls (patch testing was a poor diagnostic indicator with only 1/21 Group 1 positive). Higher cup-abduction angles (50° vs. 40°) in Group 1 were associated with higher serum Cr (p < 0.07). However, sub-optimal cup-anteversion angles (9° vs. 20°) had higher serum Co (p < 0.08). Serum Cr and Co were significantly elevated in reactive versus non-reactive Group-1 participants (p < 0.04). CD4+CD69+ T-helper lymphocytes (but not CD8+) and IL-1β, IL-12, and IL-6 cytokines were all significantly elevated in metal-reactive versus non-reactive Group 1 participants. Our results showed that lymphocyte reactivity to metals can develop within the first 1-4 years after MoM arthroplasty in asymptomatic patients and lags increases in metal ion levels. This increased metal reactivity was more prevalent in those individuals with extreme cup angles and higher amounts of circulating metal.

Cytokine secretion from human peripheral blood mononuclear cells cultured in vitro with metal particles

The failure of implanted medical devices can be associated with changes in the production of cytokines by cells of the immune system. Cytokines released by peripheral blood mononuclear cells upon contact with metal particles were quantified to understand their role in implantation intergration and their importance as messengers in the recruitment of T-lymphocytes at the implantation site. Opsonization was utilised to understand the influence of serum proteins on particle-induced cytokine production and release. Different metal compositions were used in the particulate format, Titanium (Ti), Titanium alloy (Ti6Al4V), and Stainless Steel 316L (SS), and were cultured in vitro with a mixed population of monocytes/macrophages and lymphocytes. The cells were also exposed to an exogenous stimulant mixture of phytohemagglutinin-P and interferon-gamma (IFN-γ) and opsonized particles with human serum. Interleukins, IL-1α, IL-1β, IL-2, IL-4, IL-6, IL-8, IFN-γ, and tumor necrosis factor-alpha (TNF-α) were investigated using enzyme-linked immunosorbent assay as they are an indicator of the inflammation evoked by particulate metals. It has been experimentally evidenced that metal particles induced higher amounts of IL-6 and IL-1 but very low amounts of TNF-α. T-lymphocyte activation was evaluated by the quantification of IL-2 and IFN-γ levels. The results showed that nonopsonized and opsonized metal particles did not induce the release of increased levels of IL-2 and IFN-γ.

Blockade of JNK and NFAT pathways attenuates orthopedic particle-stimulated osteoclastogenesis of human osteoclast precursors and murine calvarial osteolysis

Particles released from orthopedic implants attract immune host defense cells to the bone-implant interface and contribute to development of inflammation. The inflammatory microenvironment supports recruitment and differentiation of osteoclasts, the primary culprit of osteolysis. Therefore, understanding the complex signals that contribute to osteoclastogenesis and osteolysis is a sensible approach to design strategies to inhibit bone loss. The signaling cascades that coordinate osteoclastogenesis have been widely investigated. These include MAP kinases, Akt/PI3K pathway, NF-κB signal transduction pathway, and NFAT pathway. We have recently reported that polymethylmethacrylate (PMMA) particles activate the NFAT pathway in murine osteoclast precursors and that NFAT inhibitors dose-dependently block PMMA-induced osteoclastogenesis. In the current study, we examined the role of JNK and NFATc1 in mice in response to PMMA particles using murine calvaria model. We show that locally administered MAPK/JNK inhibitor SP600125 and calcineurin/NFAT inhibitor cyclosporine-A effectively blocked PMMA-induced osteolysis in murine calvaria. To buttress the clinical relevance of JNK/NFATc1-based regulation of PMMA-induced osteoclastogenesis, we evaluated the effect of PMMA using human macrophages. We demonstrate that SP600125 and cyclosporine-A abolished particle-induced osteoclastogenesis in human osteoclast progenitors retrieved from patients undergoing total hip replacement. Thus JNK and NFATc1 appear to act as significant mediators of orthopedic particle-induced osteolysis in humans.

Role and regulation of VEGF and its receptors 1 and 2 in the aseptic loosening of total hip implants

It was hypothesized that vascular endothelial growth factor (VEGF) in fibroblasts participates in aseptic loosening of total hip replacement (THR) implants. Therefore, osteoarthritic (OA) samples (n = 11) were compared with synovial membrane-like interface tissues from revision THR (n = 10). VEGF-A and its receptors were stained using streptavidin-immunoperoxidase method. Their regulation by hypoxia and cytokines were studied in cultured fibroblasts using quantitative real-time polymerase chain reaction (qRT-PCR). VEGFR1(+) lining cells (p < 0.01), stromal fibroblast-like cells (p = 0.001) and stromal macrophage-like cells (p < 0.05) were more numerous in rTHR than in OA. As to VEGFR2(+), only stromal fibroblast-like cells in rTHR outnumbered those found in OA (p < 0.05). VEGFRs in synovial fibroblasts were not affected by hypoxia, but VEGF increased 2.4-fold (p < 0.05). Interleukin-4 up-regulated VEGFR1 expression 23-fold. This is the first study to describe a difference between rTHR and OA in VEGF receptors, particularly VEGFR1. Hypoxia increased VEGF, but the VEGFR1 increase in the lining and stroma is probably IL-4 driven, in accordance with the M2-type macrophage dominance in interface tissues. VEGF/VEGFR system is also affected by hypoxia and may play a role in angiogenesis and bone pathology in aseptic loosening of total hip implants.

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.

Osteoclastogenesis in peripheral blood mononuclear cell cultures of periprosthetic osteolysis patients and the phenotype of T cells localized in periprosthetic tissues

Arthroplasty is a very successful medical procedure. Failures depend on aseptic loosening caused by periprosthetic osteolysis, where T cells have a contradictory role. We analyzed osteoclastogenesis in peripheral blood mononuclear cell (PBMC) cultures of periprosthetic osteolysis patients and the phenotype of T cells localized in periprosthetic tissues. We enrolled 45 subjects with periprosthetic osteolysis (15), stable prosthesis (15) and healthy controls (15). We performed PBMC cultures to study osteoclastogenesis. Osteoclasts and T cell phenotype were examined by immunohistochemistry, immunofluorescence and flow citometry. Periprosthetic osteolysis patients showed spontaneous osteoclastogenesis, which was inhibited by RANK-Fc and T cell depletion. In periprosthetic osteolysis patients' PBMC cultures, CD4 and CD8 T cells increased and CD8 T cells did not express CD25. In periprosthetic tissues T cells were close to osteoclasts, suggesting their interaction. Local CD8 T cells showed a regulatory phenotype, expressing CD25 and FoxP3, while CD4 T cells did not express activation markers. Our data suggest that, in an early stage of periprosthetic osteolysis, T cells may promote osteoclastogenesis, whereas subsequently osteoclasts activate FoxP3/CD8 T cells, which inhibit CD4 effector T cells. This mechanism may explain the previous finding of non-active T cells in periprosthetic tissues.

Effect of chromium on the level of IL-12 and IFN-gamma in occupationally exposed workers

Chromium may affect humoral and cellular immunity, acting on T lymphocytes as well as on granulocytes and monocytes cells. Cytokines play an important role in the immune balance. In this study, the level of IL-12 and IFN-gamma were evaluated in the sera and PHA/LPS stimulated culture supernatant of human PBMCs of healthy volunteers and occupationally exposed chromium workers. All the workers were highly exposed to chromium having mean of 104.65+/-77.21 microg/dL (range 23.7-316.8 microg/dL). A suspension of exposed and unexposed human PBMC (0.5x10(6) cells/ml) prepared and cultured in RPMI-1640 supplemented with 10% FCS for 18 h in the presence or absence of LPS (10 ng/ml) which used for stimulation of IL-12 and IFN-gamma. The level of IL-12 and IFN-gamma were evaluated in the sera samples as well as LPS stimulated and unstimulated culture supernatant of h-PBMCs of chromium exposed workers. In these chromium exposed workers the level of IL-12 was 433.66+/-197.49 pg/ml and 983.45+/-330.99 pg/ml in LPS stimulated culture supernatant of normal individuals and highly chromium exposed workers, which was significant (P<0.05). Although the level of IL-12 was (78.61+/-61.03 pg/ml to 146.52+/-46.37 pg/ml) elevated in unstimulated culture supernatant of h-PBMCs of chromium exposed individuals as compared to control, but it was not significant. This observation also suggests that a significant increase in IFN-gamma production in LPS stimulated and unstimulated culture supernatant of h-PBMCs of chromium exposed workers as compared to control. However, IFN-gamma level have a significant positive correlation between blood chromium level (r=0.833, t=6.3872, P 0.05) and exposure time (in years) (r=0.8916, t=8.3540, P 0.05) of the occupationally exposed workers.

Increased Expression of Toll-like Receptors in Aseptic Loose Periprosthetic Tissues and Septic Synovial Membranes Around Total Hip Implants

Objective.

Toll-like receptors (TLR) are transmembrane proteins found in various cells. They recognize infectious and endogenous threats, so-called danger signals, that evoke inflammation and assist adaptive immune reactions. It has been suggested that TLR play a role in periprosthetic tissues and arthritic synovium. Our objective was to elucidate tissue localization and functional roles of TLR in periprosthetic tissues in 2 different pathologic conditions, aseptic and septic implant loosening.

Methods.

For immunohistochemistry studies, aseptic synovial-like membranes of periprosthetic connective tissues (n = 15) and septic synovial capsular tissues (n = 5) were obtained at revision surgery and from salvage of infected totally replaced hips, respectively. Osteoarthritic synovial tissues were used for comparison (n = 5). Samples were processed for immunohistopathologic analyses for tissue colocalization of TLR with CD68 and/or CD15 using theAlexa fluorescent system. Total RNA was isolated from frozen tissues and converted into cDNA, TLR 2, 4, 5 and 9 sequences were amplified, and the products were quantified using real-time polymerase chain reaction.

Results.

Immunofluorescent staining showed colocalization of TLR 2, 4, 5, and 9 with CD68 in the focal monocyte/macrophage aggregates in aseptic synovial-like membranes from loose total hip replacements. TLR 2, 4, 5, and 9 were also found colocalized with CD15+ polymorphonuclear leukocytes and CD68+ mononuclear cells of the synovial membranes from septic total hip replacements. In osteoarthritic synovial tissues, expression of TLR was found only in vascular cells and mononuclear cells, and the reactivity was weak. mRNA levels of TLR 2, 4, 5, and 9 were increased in both aseptic and septic periprosthetic tissues. TLR 2 and 5 were significantly higher than TLR 4 and 9 in aseptic and septic samples.

Conclusion.

Peri-implant tissues were well equipped with TLR in both aseptic and septic conditions. TLR 2- and TLR 5-mediated responses seemed to dominate. In aseptic loosening, monocytes/ macrophages were the main TLR-equipped cells apparently responsible for alarmin-induced responses. This could lead to production of inflammatory cytokines and extracellular matrix-degrading proteinases after phagocytosis of wear debris derived from an implant, but in septic cases they eventually respond to microbial components. Thus, inflammatory cells in both aseptic and septic tissues were equipped with TLR, providing them with responsiveness to both endogenous and exogenous TLR ligands.

Association between apoptotis and CD4(+)/CD8(+) T-lymphocyte ratio in aseptic loosening after total hip replacement

Particle-induced osteolysis is a major cause of aseptic loosening after total joint replacement. While the osteolytic cascade initiated by cytokine release from macrophages has been studied extensively, the involvement of T-lymphocytes in this context is controversial and has been addressed by only a few authors. In a former study we detected that the quantity of T-lymphocytes may be influenced by apoptosis in patients with aseptic loosening. In this study we intended to find out more details about the apoptosis-induced shifting of the T-cell number. We focused our interest on the CD4⁺ and CD8⁺ T-cells and their relative ratio. Caspase-3 cleaved was evaluated immunohistochemically to detect apoptotic T-cells in capsules and interface membranes from patients with aseptic hip implant loosening and a varying degree of caspase-3 cleaved expression in CD4⁺ and CD8⁺ T-lymphocytes was detected. Moreover, a relationship between the intensity of the apoptotic reactions and the radiological extent of osteolysis was observed. The number of CD4⁺ cells was decreased in the presence of strong apoptotic reactions, respectively extensive osteolysis, while CD8⁺ cells were affected to a much lower degree. Thus, the CD4⁺/CD8⁺ ratio changed from 1.0 in cases with only small areas of periprosthetic osteolysis and minimally intense apoptosis to 0.33 in cases with large areas of osteolysis. This may suggest a causal relationship between the apoptosis-induced shift in the CD4⁺/CD8⁺ ratio and the osteolysis respectively aseptic loosening. It is possible that these findings may lead to a new understanding of particle-induced osteolysis.

The combined role of wear particles, macrophages and lymphocytes in the loosening of total joint prostheses

This review considers the causes of loosening of prosthetic joint replacement paying attention to the biological mechanisms rather than other effects that are physical, such as component fracture and other failure related to mechanical problems. Infection accounts for approximately 1.5 per cent of joint loosening and when it occurs it is a cause of serious concern to the surgeon. The loosening of prosthetic joints in the absence of infection is by far the most common reason for revision surgery and is known as aseptic loosening. While this may be multifactorial in terms of causation, and non-biological factors may contribute significantly in a particular individual, a significant part is undoubtedly played by the generation of wear debris, mainly from the bearing surfaces of the joint, and the cellular reaction to this in the implant bed. Phagocytic cells (macrophages and multinucleated giant cells) are the ones that remove foreign material from the tissues, and the ways in which these cells function in the interface between implant and bone are described. Mediators produced locally include numerous cytokines, enzymes and integrins. There is evidence for interactions between macrophages and locally recruited lymphocytes, which may or may not give rise to an immunologically mediated process.Sensitization of individuals having metal implants in place has been shown by positive skin tests or blood lymphocyte transformation tests and in these cases has been accompanied by loosening and failure of the replacement joint. The question remains as to whether this process is also present in a proportion of individuals with aseptic loosening in the absence of clearly defined clinical evidence of sensitization.Numerous studies performed by the author's group and, latterly, by others suggest that the cellular reactions detected in the tissues in cases of aseptic loosening are indeed those of contact sensitization. There is good evidence to show that a type IV cell-mediated immune reaction is taking place, with TH1 cell involvement and active antigen presentation. The extent to which sensitization is present in individual cases of aseptic loosening remains a subject for further work and this needs all the sophisticated molecular methods now available to modern biology to be applied in appropriate prospective clinical studies coupled with experimental models in vitro and in vivo. Immunological processes may play a more important part in joint loosening than previously considered.

NFAT2 is an essential mediator of orthopedic particle-induced osteoclastogenesis

Particle-induced periprosthetic osteolysis is the major cause for orthopedic implant failure. This failure is mediated mainly by the action of osteoclasts, the principal cells responsible for bone resorption and osteolysis. Therapeutic interventions to alleviate osteolysis have been focused on understanding and targeting mechanisms of osteoclastogenesis. The nuclear transcription factor NFAT is an essential terminal differentiation factor of osteoclastogenesis. This transcription factor is known to cooperate with c-jun/AP-1 in mediating RANKL-induced osteoclastogenesis. We have previously determined that RANKL is an essential cytokine mediator of particle-induced osteoclastogenesis, and that PMMA particles activate JNK and c-jun/AP-1 in bone marrow macrophages (osteoclast precursors). In the current study, we investigated the effect of PMMA particles on the NFAT signaling pathway in osteoclast precursor cells. Our findings point out that PMMA particles stimulate nuclear translocation of NFAT2 in wild-type osteoclast precursors, which is associated with increased osteoclastogenesis. More importantly, induction of osteoclastogenesis was selectively blocked in a dose-dependent fashion by the calcineurin inhibitors, Cyclosporine-A and FK506. Further, this activation was also blocked in a time-dependent fashion by the NFAT inhibitor VIVIT. Finally, we provide novel evidence that PMMA particles induce binding of NFAT2 and AP-1 proteins. Thus, our findings demonstrate that activation of the NFAT pathway in conjunction with MAP kinases is essential for basal and PMMA-stimulated osteoclastogenesis.

Th1 type lymphocyte reactivity to metals in patients with total hip arthroplasty

BACKGROUND

All prostheses with metallic components release metal debris that can potentially activate the immune system. However, implant-related metal hyper-reactivity has not been well characterized. In this study, we hypothesized that adaptive immunity reaction(s), particularly T-helper type 1 (Th1) responses, will be dominant in any metal-reactivity responses of patients with total joint replacements (TJAs). We tested this hypothesis by evaluating lymphocyte reactivity to metal "ions" in subjects with and without total hip replacements, using proliferation assays and cytokine analysis.

METHODS

Lymphocytes from young healthy individuals without an implant or a history of metal allergy (Group 1: n = 8) were used to assess lymphocyte responses to metal challenge agents. In addition, individuals (Group 2: n = 15) with well functioning total hip arthroplasties (average Harris Hip Score = 91, average time in-situ 158 months) were studied. Age matched controls with no implants were also used for comparison (Group 3, n = 8, 4 male, 4 female average age 70, range 49-80). Group 1 subjects' lymphocyte proliferation response to Aluminum+3, Cobalt+2, Chromium+3, Copper+2, Iron+3, Molybdenum+5, Manganeese+2, Nickel+2, Vanadium+3 and Sodium+2 chloride solutions at a variety of concentrations (0.0, 0.05, 0.1, 0.5, 1.0 and 10.0 mM) was studied to establish toxicity thresholds. Mononuclear cells from Group 2 and 3 subjects were challenged with 0.1 mM CrCl3, 0.1 mM NiCl2, 0.1 mM CoCl2 and approx. 0.001 mM titanium and the reactions measured with proliferation assays and cytokine analysis to determine T-cell subtype prominence.

RESULTS

Primary lymphocytes from patients with well functioning total hip replacements demonstrated a higher incidence and greater magnitude of reactivity to chromium than young healthy controls (p < 0.03). Of the 15 metal ion-challenged subjects with well functioning total hip arthroplasties, 7 demonstrated a proliferative response to Chromium, Nickel, Cobalt and/or Titanium (as defined by a statistically significant >2 fold stimulation index response, p < 0.05) and were designated as metal-reactive. Metals such as Cobalt, Copper, Manganese, and Vanadium were toxic at concentrations as low as 0.5 mM while other metals, such as Aluminum, Chromium, Iron, Molybdenum, and Nickel, became toxic at much higher concentrations (>10 mM). The differential secretion of signature T-cell subsets' cytokines (Th1 and Th2 lymphocytes releasing IFN-gamma and IL-4, respectively) between those total hip arthroplasty subjects which demonstrated metal-reactivity and those that did not, indicated a Th1 type (IFN-gamma) pro-inflammatory response.

CONCLUSION

Elevated proliferation and production of IFN-gamma to metals in hip arthroplasty subjects' lymphocytes indicates that a Th1 (vs. Th2) type response is likely associated with any metal induced reactivity. The involvement of an elevated and specific lymphocyte response suggests an adaptive (macrophage recruiting) immunity response to metallic implant debris rather than an innate (nonspecific) immune response.

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.

Mechanisms of Disease: molecular insights into aseptic loosening of orthopedic implants

Despite the success of treating rheumatic disorders with biologic therapies, joint replacement surgery still remains the final treatment option in many cases. Approximately 1.5 million joint arthroplastic operations are performed annually worldwide. Implant failure due to massive bone loss and aseptic loosening of prostheses, however, is a major complication of joint replacement, which can lead to high socioeconomic burdens both for the individual patient and for health-care systems. To date, there is no approved drug therapy to prevent or inhibit periprosthetic osteolysis, and aseptic loosening of prostheses can only be overcome by surgical revision. Research during the past decade, however, has unravelled much of the pathogenesis of aseptic prosthesis loosening and preclinical studies have identified potential targets for pharmaceutical treatments. This article highlights the importance of a cooperative interaction between rheumatologists and orthopedic surgeons, and presents novel insights into the molecular mechanisms behind aseptic loosening of prostheses. In addition, we outline potential perspectives for the development of future therapeutic strategies for this devastating complication.

Aseptic loosening of total joint replacements: mechanisms underlying osteolysis and potential therapies

Total joint replacement, although considered an excellent surgical procedure, can be complicated by osteolysis induced by implant particles and subsequent aseptic loosening of the implant. The pathogenesis of implant-associated osteolysis includes inflammatory and osteolytic processes. The sustained chronic inflammatory response initiated by particulate debris at the implant-bone interface is manifested by recruitment of a wide array of cell types. These cells include macrophages, fibroblasts, giant cells, neutrophils, lymphocytes, and--most importantly--osteoclasts, which are the principal bone resorbing cells. The 'cellular response' entails secretion of osteoclastogenic and inflammatory cytokines that favor exacerbated osteoclast activity and enhanced osteolysis. An appreciation of the complex network that leads to these cellular and inflammatory responses will form a foundation on which to develop therapeutic interventions to combat inflammatory periprosthetic bone loss.

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.

Toll-like receptors in the interface membrane around loosening total hip replacement implants

Toll-like receptors (TLRs) have been known to act as sensors of innate immunity and respond to ligands of microbial and endogenous components. Tissues and cells typical for interface membrane of foreign body reaction were analyzed to evaluate potential role of TLRs in the pathogenesis of the so called "aseptic loosening of total hip replacement." Fourteen cases of interface membrane around aseptic loose total hip replacement implants were stained by single and double immunohistochemical methods to examine cellular localization of toll-like receptor (TLR)-4 and TLR-9. Osteoarthritic synovium was used as control tissues. Cultured macrophages were used to study TLR-4 and TLR-9 mRNA levels by quantitative reverse transcriptase-polymerase chain reaction. The effect of titanium particle stimulation on macrophages was also examined in the culture. Extensive immunolocalization of TLR-4 and TLR-9 positive cells was observed in the synovial membrane-like interface membrane of foreign body granulomas compared with control synovial membranes. TLR and CD68 double staining demonstrated that the TLR positive cells in aseptic loosening were mostly monocyte/macrophages and foreign body giant cells. TLR-4 and TLR-9 mRNA expression was also found in macrophage-colony stimulating factor treated rat macrophages, but this expression decreased (p < 0.05 or less) upon stimulation with titanium particles although matrix metalloproteinase (MMP)-9 mRNA levels used as macrophage activation marker were increased (p = 0.01). The interface membrane around loosening total hip replacement implants is apparently well equipped with TLRs and, thus, probably very sensitive to various structural components of microbes and to endogenous TLR ligands. This seems to be due to recruitment of monocyte/macrophages as particles per se seemed to down-regulate some of the key TLRs. This suppression after particle phagocytosis might prevent excessive and harmful host responses, and injury to innocent bystander cells/tissues.

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.

Host inflammatory response to NiCr, CoCr, and Ti in a soft tissue implantation model

The inflammatory response to nickel chromium (NiCr), cobalt chromium (CoCr), and titanium (Ti) implants at 7 and 28 days was investigated using real-time PCR analysis along with histological and immunohistochemical staining. Contrasting inflammatory profiles were found in response to the different metal compositions. The inflammatory profile induced by CoCr remained consistent and elevated during the 28-day period with high cell counts associated with the implants and a progressive recruitment of T lymphocytes. The response to NiCr was also elevated, but with an initially low T-lymphocyte infiltration that increased by the later time period. Ti indicated an early increased inflammatory response that had reduced by 28 days. Changes in gene expression demonstrated that Ti induced very low levels of expression of the three inflammatory cytokine genes. NiCr initiated a significant upregulation in gene expression for IL-6 and TNF-alpha. CoCr resulted in the highest upregulation of IL-2 indicative of T-lymphocyte activation to this material.

The microenvironment around total hip replacement prostheses

The metal stem of the totally replaced hip carries load and resists fatigue, but it is electrochemically corroded. Metallic atoms act as haptens, induce type 1 T-helper cells/Th1-type immune responses and enhance periprosthetic osteolysis. Stiff metal implants, which do not have the same elasticity as the surrounding bone, cause stress shielding. Cyclic loading and lack of ligamentous support lead to mechanical and ischemia reperfusion injury and particle formation from bone, polymethylmethacrylate, and porous implant surfaces, which accelerate third-body polyethylene wear. Surgical injury and micromotion induce the formation of a fibrous capsule interface. Type-B lining cells produce lubricin and surface-active phospholipids to promote solid-to-solid lubrication but may loosen the implant from bone. The pumping action of the cyclically loaded joint and synovial fluid pressure waves dissect the implant-host interface and transports polyethylene particles and pro-inflammatory mediators to the interface. Hyaluronan induces formation of a synovial lining like layer. Because of its localization close to bone, foreign body inflammation at the interface stimulates osteoclastogenesis and peri-implant bone loss. Metal-on-metal and ceramic-on-ceramic pairs might minimize third body wear, but can lead to high-impact load of the acetabulum. Diamond coating of a metal-on-polyethylene couple might solve both of these problems. The basic biomaterial solutions allow good mechanical performance and relatively long life in-service, but surface modifications (porous coating, hydroxyapatite, diamond, bioglass, and others) may facilitate performance of the implant and improve the biomaterial and body interfaces.