Trends of mechanical consequences and modeling of a fibrous membrane around femoral hip prostheses

In the present study, the effects of a fibrous membrane between cement and bone in a femoral total hip replacement were investigated. The study involved the problem of modeling this fibrous membrane in finite-element analyses, and its global consequences for the load-transfer mechanism and its resulting stress patterns. A finite-element model was developed, suitable to describe nonlinear contact conditions in combination with nonlinear material properties of the fibrous membrane. The fibrous tissue layer was described as a highly compliant material with little resistance against tension and shear. The analysis showed that the load transfer mechanism from stem to bone changes drastically when such a membrane is present. These effects are predominantly caused by tensile loosening and slip at the interface, and are enhanced by the nonlinear membrane characteristics.\ud \ud Using parametric analysis, it was shown that these effects on the load-transfer mechanism cannot be described satisfactorily with linear elastic models.\ud \ud Most importantly, the fibrous tissue interposition causes excessive stress concentrations in bone and cement, and relatively high relative displacements between these materials

Kinetics of human myeloid-derived suppressor cells after blood draw

Background: Human myeloid-derived suppressor cells (MDSC) have been described as a group of immature myeloid cells which exert immunosuppressive action by inhibiting function of T lymphocytes. While there is a huge scientific interest to study these cells in multiple human diseases, the methodological approach varies substantially between published studies. This is problematic as human MDSC seem to be a sensible cell type concerning not only cryopreservation but also time point after blood draw. To date data on delayed blood processing influencing cell numbers and phenotype is missing. We therefore evaluated the kinetics of granulocytic MDSC (gMDSC) and monocytic MDSC (mMDSC) frequencies after blood draw in order to determine the best time point for analysis of this recently defined cell type. Methods: In this study, we isolated peripheral blood mononuclear cells (PBMC) of patients with HIV infection or solid tumors directly after blood draw. We then analyzed the frequencies of gMDSC and mMDSC 2, 4 and 6 h after blood draw and after an overnight rest by FACS analysis using the standard phenotypic markers. In addition, part of the cells was frozen directly after PBMC preparation and was measured after thawing. Results: gMDSC levels showed no significant difference using fresh PBMC over time with a limitation for the overnight sample. However they were massively diminished after freezing (p = 0.0001 for all subjects). In contrast, frequencies of fresh mMDSC varied over time with no difference between time point 2 and 4 h but a significantly reduction after 6 h and overnight rest (p = 0.0005 and p = 0.005 respectively). Freezing of PBMC decreased the yield of mMDSC reaching statistical significance (p = 0.04). For both MDSC subgroups, FACS analysis became more difficult over time due to less sharp divisions between populations. Conclusions: According to our data human MDSC need to be studied on fresh PBMC. gMDSC can be studied with delay, mMDSC however should be studied no later than 4 h after blood draw. These results are crucial as an increasing number of clinical trials aim at analyzing MDSC nowadays and the logistics of blood processing implies delayed sample processing in some cases

Quantitative analysis of bone reactions to relative motions at implant-bone interfaces

Connective soft tissues at the interface between implants and bone, such as in human joint replacements, can endanger the stability of the implant fixation. The potential of an implant to generate interface bone resorption and form soft tissue depends on many variables, including mechanical ones. These mechanical factors can be expressed in terms of relative motions between bone and implant at the interface or deformation of the interfacial material.\ud \ud The purpose of this investigation was to determine if interface debonding and subsequent relative interface motions can be responsible for interface degradation and soft tissue interposition as seen in experiments and clinical results. A finite element computer program was augmented with a mathematical description of interface debonding, dependent on interface stress criteria, and soft tissue interface interposition, dependent on relative interface motions. Three simplified models of orthopaedic implants were constructed: a cortical bone screw for fracture fixation plates, a femoral resurfacing prosthesis and a straight stem model, cemented in a bone. The predicted computer configurations were compared with clinical observations. The computer results showed how interface disruption and fibrous tissue interposition interrelate and possibly enhance each other, whereby a progressive development of the soft tissue layer can occur.\ud \ud Around the cortical bone screw, the predicted resorption patterns were relatively large directly under the screw head and showed a pivot point in the opposite cortex. The resurfacing cup model predicted some fibrous tissue formation under the medial and lateral cup rim, whereby the medial layer developed first because of higher initial interface stresses. The straight stem model predicted initial interface failure at the proximal parts. After proximal resorption and fibrous tissue interposition, the medial interface was completely disrupted and developed an interface layer. The distal and mid lateral side maintained within the strength criterion.\ud \ud Although the applied models were relatively simple, the results showed reasonable qualitative agreement with resorption patterns found in clinical studies concerning bone screws and the resurfacing cup. The hypothesis that interface debonding and subsequent relative (micro)motions could be responsible for bone resorption and fibrous tissue propagation is thereby sustained by the results

High frequencies of PMN-MDSCs are associated with low suppressive capacity in advanced stages of HIV-1 infection

Background Polymorphonuclear myeloid-derived suppressor cells (PMN-MDSCs) are an immature cell type that inhibits the effector functions of T lymphocytes in chronic HIV infection. A well-known immunological feature of the disease course is the development of immune exhaustion, which is correlated with excessive immune activation in late-stage disease. Here, we hypothesized that immune exhaustion would also affect PMN-MDSCs in late-stage HIV-1 infection. Methods We evaluated untreated chronically HIV-infected patients (progressors, n = 10) and control groups (controllers, patients with non-small cell lung carcinoma and healthy controls, n = 16) with regard to levels of PMN-MDSCs and their inhibitory potential. Additionally, we studied CD8 T cell effector functions (interferon-gamma, TNF alpha, IL-2 and CD107) and parameters of CD8 T cell activation (CD38 and HLA-DR) and exhaustion (PD-1 and LAG-3) by flow cytometry. Plasma inflammation markers analyzed here were IL-6, IL-8, soluble CD14, highly sensitive CRP, and cystatin C. Results Coincubation experiments with isolated PMN-MDSCs led to a significant inhibition of CD8 T cell proliferation (p < 0.0001), with a significant correlation between PMN-MDSC frequency and suppressive capacity: the higher the frequency of PMN-MDSCs was, the lower the suppressive capacity (rho = 0.51, p = 0.0082). Stratifying all study subjects into subgroups with PMN-MDSC frequencies above or below 2.5% resulted in a significantly increased suppressive capacity in patients with frequencies below 2.5% (p = 0.021). While there was no correlation with the cellular activation markers CD38 and HLA-DR, high IL-8 levels were significantly associated with high PMN-MDSC frequencies (rho = 0.52, p = 0.0074) and low suppressive capacity (rho = 0.47, p = 0.019). Conclusions In this study, we demonstrate for the first time that PMN-MDSCs show limited effector functions in advanced disease stages of HIV infection. The hyperactive immune state is associated with this loss of function. However, we show an association with the proinflammatory cytokine IL-8, which is an important factor for the migration and adhesion of polymorphonuclear cells

Fully Differentiated HIV-1 Specific CD8+ T Effector Cells are More Frequently Detectable in Controlled than in Progressive HIV-1 Infection

Background: CD8+ T cells impact control of viral infections by direct elimination of infected cells and secretion of a number of soluble factors. In HIV-1 infection, persistent HIV-1 specific IFN-γ+ CD8+ T cell responses are detected in the setting of disease progression, consistent with functional impairment in vivo. Recent data suggest that impaired maturation, as defined by the lineage markers CD45RA and CCR7, may contribute to a lack of immune control by these responses. Methodology/Principal Findings: We investigated the maturation phenotype of epitope-specific CD8+ T cell responses directed against HIV-1 in 42 chronically infected, untreated individuals, 22 of whom were “Controllers” (median 1140 RNA copies/ml plasma, range less than 50 to 2520), and 20 “progressors” of whom had advanced disease and high viral loads (median 135,500 RNA copies/ml plasma, range 12100 to greater than 750000). Evaluation of a mean of 5 epitopes per person revealed that terminally differentiated CD8+ T cells directed against HIV-1 are more often seen in HIV-1 Controllers (16/22; 73%) compared to HIV-1 progressors (7/20; 35%)(p = 0.015), but the maturation state of epitope-specific responses within a given individual was quite variable. Maturation phenotype was independent of the HLA restriction or the specificity of a given CD8+ T cell response and individual epitopes associated with slow disease progression were not more likely to be terminally differentiated. Conclusions/Significance: These data indicate that although full maturation of epitope-specific CD8+ T cell responses is associated with viral control, the maturation status of HIV-1 specific CD8+ T cell responses within a given individual are quite heterogeneous, suggesting epitope-specific influences on CD8+ T cell function

Nef-specific CD45RA+ CD8+ T cells secreting MIP-1β but not IFN-γ are associated with nonprogressive HIV-1 infection

<p>Abstract</p> <p>Background</p> <p>Long-term survival of HIV-1 infected individuals is usually achieved by continuous administration of combination antiretroviral therapy (ART). An exception to this scenario is represented by HIV-1 infected nonprogressors (NP) which maintain relatively high circulating CD4+ T cells without clinical symptoms for several years in the absence of ART. Several lines of evidence indicate an important role of the T-cell response in the modulation of HIV-1 infection during the acute and chronic phase of the disease.</p> <p>Results</p> <p>We analyzed the functional and the differentiation phenotype of Nef- and Tat-specific CD8+ T cells in a cohort of HIV-1 infected NP in comparison to progressors, ART-treated seropositive individuals and individuals undergoing a single cycle of ART interruption. We observed that a distinctive feature of NP is the presence of Nef-specific CD45RA+ CD8+ T cells secreting MIP-1beta but not IFN-gamma. This population was present in 7 out of 11 NP. CD45RA+ IFN-gamma^negMIP-1beta+ CD8+ T cells were not detected in HIV-1 infected individuals under ART or withdrawing from ART and experiencing a rebounding viral replication. In addition, we detected Nef-specific CD45RA+ IFN-gamma^negMIP-1beta+ CD8+ T cells in only 1 out of 10 HIV-1 infected individuals with untreated progressive disease.</p> <p>Conclusion</p> <p>The novel antigen-specific CD45RA+ IFN-gamma^negMIP-1beta+ CD8+ T cell population represents a new candidate marker of long-term natural control of HIV-1 disease progression and a relevant functional T-cell subset in the evaluation of the immune responses induced by candidate HIV-1 vaccines.</p

Particular Characterisation of an In-Vitro-DTH Test to Monitor Cellular Immunity - Applications for Patient Care and Space Flight

Goal:i) Characterization of the role of the main immune reactive cell types contributing to the cellular immune response in the in-vitro DTH and ii) Validation of the in-vitro DTH under different clinical and field conditions. Methods:As positive control whole blood was incubated in the in-vitro DTH, supernatants were gathered after 12, 24 and 48h. Readout parameters of this test are cytokines in the assay's supernatant. To determine the role of T-cells, monocytes and natural killer (NK), these cell populations were depleted using magnetic beads prior to in-vitro-DTH incubation. Validation of the test has occurred under clinical (HIV-patients, ICU) and field-conditions (parabolic/space-flights, confinement). Results:T-cell depletion abandoned almost any IL-2 production and reduced IFN-gamma production irrespective of the type of antigen, whereas CD56 depleted cultures tended to lower IL-2 secretion and IFN-gamma and to parallel a IL-10-increase after viral challenge. This IL-10-increase was seen also in CD14-depleted setups. DTH read-out was significantly different under acute stress (parabolic flight) or chronic stress (ISS), respectively. Preliminary data of HIV infected patients demonstrate that this test can display the contemporary immune status during an antiviral therapy. Conclusion:The in-vitro DTH mirrors adaptive and innate immune activation and may serve as tool also for longitudinal follow up of Th1/Th2 weighed immune response under adverse life conditions on earth and in space. It is planned to implement the assay in the on the ISS (MoCISS)

Treatment intensification in HIV-infected Patients is associated With reduced Frequencies of regulatory T cells

In untreated HIV infection, the efficacy of T cell responses decreases over the disease course, resulting in disease progression. The reasons for this development are not completely understood. However, immunosuppressive cells are supposedly crucially involved. Treatment strategies to avoid the induction of these cells preserve immune functions and are therefore the object of intense research efforts. In this study, we assessed the effect of treatment intensification [= 5-drug antiretroviral therapy (ART)] on the development of suppressive cell subsets. The New Era (NE) study recruited patients with primary HIV infection (PHI) or chronically HIV-infected patients with conventional ART (CHI) and applied an intensified 5-drug regimen containing maraviroc and raltegravir for several years. We compared the frequencies of the immune suppressive cells, namely, the myeloid-derived suppressor cells (MDSCs), regulatory B cells (Bregs), and regulatory T cells (Tregs), of the treatment intensification patients to the control groups, especially to the patients with conventional 3-drug ART, and analyzed the Gag/Nef-specific CD8 T cell responses. There were no differences between PHI and CHI in the NE population (p > 0.11) for any of the studied cell types. Polymorphonuclear myeloid-derived suppressor cell (PMN-MDSC), monocytic myeloid-derived suppressor cell (M-MDSC), and the Breg frequencies were comparable to those of patients with a 3-drug ART. However, the Treg levels were significantly lower in the NE patients than those in 3ART-treated individuals and other control groups (p = 0.0033). The Gag/Nef-specific CD8 T cell response was broader (p = 0.0134) with a higher magnitude (p = 0.026) in the NE population than that in the patients with conventional ART. However, we did not find a correlation between the frequency of the immune suppressive cells and the interferon-gamma+ CD8 T cell response. In the treatment intensification subjects, the frequencies of the immune suppressive cells were comparable or lower than those of the conventional ART-treated subjects, with surprisingly broad HIV-specific CD8 T cell responses, suggesting a preservation of immune function with the applied treatment regimen. Interestingly, these effects were seen in both treatment intensification subpopulations and were not attributed to the start of treatment in primary infection