David Philip Lowe

Blood levels of donor-specific human leukocyte antigen antibodies after renal transplantation : Resolution of rejection in the presence of circulating donor-specific antibody

Background. Accommodation to antibody is an important mechanism in successful ABO-incompatible transplantation, but its importance in human leukocyte antigen (HLA) antibody-incompatible transplantation is less clear, as sensitive techniques facilitating daily measurement of donor-specific HLA antibodies (DSAs) have only recently been developed. Methods. We report 24 patients who had HLA antibody-incompatible kidney transplantation (21 living donors, 3 deceased), 21 of whom had pretransplant plasmapheresis. Eight had positive complement-dependent cytotoxic (CDC) crossmatch (XM) pretransplant plasmapheresis, nine had positive flow cytometric (FC) XM, and seven had DSA detectable by microbead analysis only. After transplant, DSA levels were monitored closely with microbead assays. Results. Rejection occurred in five of eight (62.5%) CDC-positive cases, in three of nine (33%) FC-positive cases, and in two of seven (29%) of microbead-only cases at a median of 6.5 days after transplantation. Resolution occurred at a median of 15 days after transplantation, in 8 of 10 cases when the microbead level of DSA had median fluorescence intensity (MFI) >2000 U, in 6 of 10 when the microbead MFI >4000 U. In 8 of 10 cases, the microbead MFI at the time of resolution was greater than at the onset. DSA did not always cause clinical rejection. In five cases with a posttransplant DSA peaking at MFI >2000 U on microbead assay, rejection did not occur. Conclusion. These data suggest that the dominant method of successful transplantation was function of the transplant in the presence of circulating DSA, and they also define the period during which this occurred.

Human leukocyte antigen antibody-incompatible renal transplantation: excellent medium-term outcomes with negative cytotoxic crossmatch.

Background. Human leukocyte antigen (HLA) antibody-incompatible renal transplantation has been increasingly performed since 2000 but with few data on the medium-term outcomes. Methods. Between 2003 and 2011, 84 patients received renal transplants with a pretreatment donor-specific antibody (DSA) level of more than 500 in a microbead assay. Seventeen patients had positive complement-dependent cytotoxic (CDC) crossmatch (XM), 44 had negative CDC XM and positive flow cytometric XM, and 23 had DSA detectable by microbead only. We also reviewed 28 patients with HLA antibodies but no DSA at transplant. DSAs were removed with plasmapheresis pretransplant, and patients did not routinely receive antithymocyte globulin posttransplant. Results. Mean follow-up posttransplantation was 39.6 (range 2–91) months. Patient survival after the first year was 93.8%. Death-censored graft survival at 1, 3, and 5 years was 97.5%, 94.2%, and 80.4%, respectively, in all DSA+ve patients, worse at 5 years in the CDC+ve than in the CDC−ve/DSA+ve group at 45.6% and 88.6%, respectively (P<0.03). Five-year graft survival in the DSA−ve group was 82.1%. Rejection occurred in 53.1% of DSA+ve patients in the first year compared with 22% in the DSA−ve patients (P<0.003). Conclusions. HLA antibody-incompatible renal transplantation had a high success rate if the CDC XM was negative. Further work is required to predict which CDC+ve XM grafts will be successful and to treat slowly progressive graft damage because of DSA in the first few years after transplantation.

Significant IgG subclass heterogeneity in HLA-specific antibodies: Implications for pathogenicity, prognosis, and the rejection response

IgG subclasses differ in their ability to fix complement and bind Fc receptors. This study describes a detailed analysis of the distribution of HLA-specific IgG subclasses in order to define how this varies in sensitised waiting-list patients. We found significant variation in the level, presence and combinations of each HLA-specific IgG subclass between and within individuals and this is influenced by the type of sensitising event. Graft failure in particular provokes higher levels of IgG1 (vs transfusion, p=0.071 and pregnancy, p=0.042), IgG2 (vs transfusion, p=0.001 and pregnancy, p=0.016), and IgG4 (vs transfusion, p=0.052). Both graft failure and pregnancy tend to stimulate multiple IgG subclass responses against HLA, whereas transfusion stimulated antibodies are dominated by responses limited to IgG1 (p=0.033) and have a low incidence of IgG4 (p=0.046). In marked contrast, IgG4 characterised nearly all HLA DQ-specific antibodies stimulated by graft rejection (p=0.006). Such widely varying IgG subclass heterogeneity is likely to be due to underlying immunological processes dependent on the route of sensitisation. This diversity, which implies functional variation, may help explain why HLA-specific antibodies are an obstacle to transplantation in some circumstances but not others. The subclass association with rejection has potential as a biomarker for chronic rejection.

A dynamic analysis of resonant tunnelling

The growing interest in resonant tunnelling devices that are expected to operate at high frequencies highlights the small amount of work that has previously been performed in an attempt to understand the dynamics of resonant tunnelling in quantum mechanical systems. In this paper the authors present a numerical and analytical treatment of the dynamics of resonant tunnelling, and contrast the result with those of alternative approaches to the problem. The analysis presented shows that resonant tunnelling does not require a precondition as proposed by previous authors. Two pictures of resonant tunnelling emerge, one of which is a hopping-type process whilst the other is described as true resonant tunnelling. In both pictures the relevant time which describes the dynamic resonant tunnelling may be taken to be 2h(cross)/ Gamma where Gamma is the width of the resonance.

Rises and falls in donor-specific and third-party HLA antibody levels after antibody incompatible transplantation

Background. After human leukocyte antigen (HLA) antibody-incompatible transplantation, donor specific and third party HLA antibodies may be found, and their levels fall in a donor-specific manner during the first month. However, these changes have not been previously described in detail. Methods. Donor-specific HLA antibody (DSA) and third-party HLA antibody (TPA) levels were measured using the microbead method in 44 presensitized patients who had renal transplantation. Results. DSA+TPA fell in the first 4 days after transplantation, and greater falls in DSA indicated absorption by the graft. This occurred for class I (57.8% fall compared with 20.2% for TPA, P<0.0005), HLA DR (63.0% vs. 24.3%, P<0.0004), and for HLA DP/DQ/DRB3–4 (34% vs. 17.5%, P=0.014). Peak DSA levels occurred at a mean of 13 days posttransplant, and they were higher than pretreatment in 25 (57%) patients and lower in 19 (43%) patients (P=ns). The risk of rejection was associated with peak DSA levels; 15 of 25 (60%) patients with DSA at median fluorescence intensity (MFI) more than 7000U experienced rejection, compared with 4 of 7 (57%) patients with peak DSA MFI 2000 to 7000U, and 2 of 12 (17%) patients with peak DSA MFI less than 2000U (P<0.02). DSA levels subsequently fell in a donor specific manner compared to TPA. Conclusion. DSA levels may change markedly in the first month after antibody incompatible transplantation, and the risk of rejection was associated with higher pretreatment and peak levels.

Double Filtration Plasmapheresis in Antibody-Incompatible Kidney Transplantation

Double filtration plasmapheresis (DFPP) was used in preference to plasma exchange in our program of antibody‐incompatible transplantation, to treat higher volumes of plasma. Forty‐two patients had 259 sessions of DFPP, 201 pre‐transplant and 58 post‐transplant. At the first treatment session, the mean plasma volume treated was 3.81 L (range 3–6 L), 55.5 mL/kg (range 36.2–83.6 mL/kg). Serum IgG fell by mean 59.4% (SD 10.2%), and IgM by 69.3% (SD 16.1%). Nine patients did not require increases in plasma volumes treated, and six did not tolerate higher plasma volumes. In the remaining patients, the mean maximum plasma volume treated pre‐transplant was 6.67 L (range 4–15 L), 96.1 mL/kg (range 60.2–208.9 mL/kg). The complement dependent cytotoxic crossmatch was positive in 14 cases pre‐treatment, and remained positive in six (42.8%) cases. The flow cytometric crossmatch was positive in 29 cases pre‐treatment, and in 21 (72.4%) after DFPP. Post‐transplant, DFPP was ineffective at reducing donor specific antibody levels during periods of rapid donor specific antibody synthesis. Post‐transplant, the one year graft survival rate was 94%, although there was a high rate of early rejection. In summary, DFPP enabled the treatment of plasma volumes that were almost double those that would have been feasible with plasma exchange. Despite this, most patients were transplanted with a positive crossmatch, and DFPP post‐transplant was unable to control rising antibody levels.

Subclass analysis of donor HLA-specific IgG in antibody-incompatible renal transplantation reveals a significant association of IgG4 with rejection and graft failure.

Donor HLA‐specific antibodies (DSAs) can cause rejection and graft loss after renal transplantation, but their levels measured by the current assays are not fully predictive of outcomes. We investigated whether IgG subclasses of DSA were associated with early rejection and graft failure. DSA levels were determined pretreatment, at the day of peak pan‐IgG level and at 30 days post‐transplantation in eighty HLA antibody‐incompatible kidney transplant recipients using a modified microbead assay. Pretreatment IgG4 levels were predictive of acute antibody‐mediated rejection (P = 0.003) in the first 30 days post‐transplant. Pre‐treatment presence of IgG4 DSA (P = 0.008) and day 30 IgG3 DSA (P = 0.03) was associated with poor graft survival. Multivariate regression analysis showed that in addition to pan‐IgG levels, total IgG4 levels were an independent risk factor for early rejection when measured pretreatment, and the presence of pretreatment IgG4 DSA was also an independent risk factor for graft failure. Pretreatment IgG4 DSA levels correlated independently with higher risk of early rejection episodes and medium‐term death‐censored graft survival. Thus, pretreatment IgG4 DSA may be used as a biomarker to predict and risk stratify cases with higher levels of pan‐IgG DSA in HLA antibody‐incompatible transplantation. Further investigations are needed to confirm our results.

Association of killer cell immunoglobulin-like receptors with primary Sjögren's syndrome

OBJECTIVE SS is a chronic inflammatory condition characterized by systemic and tissue-specific autoimmune features. In view of recent findings indicating a role for killer cell immunoglobulin-like receptors (KIRs) in the pathogenesis of other autoimmune rheumatic disorders such as SSc, and the autoimmune disorders RA and PsA, we sought to determine whether KIRs predict general or specific susceptibility in SS. METHODS Eleven separate KIR genes were typed using PCR sequence-specific primers on genomic DNA from 72 patients diagnosed with primary SS and a control panel consisting of 223 blood donors. RESULTS We found no individual KIR genes to be associated with SS. In contrast, 11 patients with primary SS (15%) and 9 control blood donors (4%) had KIR genotypes with the activating KIR2DS2 in the absence of its corresponding inhibitory homologue KIR2DL2 (P = 0.01). Further analysis of these individuals showed that seven SS patients were positive for HLA-C ligand for KIR2DS2 only compared with one control sample (P = 0.00026). CONCLUSION The genetic combination of KIR2DS2+ and KIR2DL2- in the presence of HLA-C ligand specific for activating KIR2DS2 is associated with primary SS. This implies that autologous KIR-ligand interaction is a contributory factor to predisposition for this disease.

A model study of field-dependent dynamical screening due to mobile electrons in submicron semiconductor devices

A previously obtained generalised field-dependent screening function involving one-electron Wigner distributions and spectral functions is studied under various model approximations. The field dependence of the screening arises from the action of a (constant) electric field within duration of a collision process (estimated from the uncertainty relations) and has the effect of reducing the screening efficiency. This field-induced descreening effect is studied analytically and numerically for a range of electric field strengths and electron temperatures and densities in both three- and two-dimensional non-degenerate electron assemblies. The model assumed allows the influences of displaced Maxwellian distribution functions and finite electron quasiparticle lifetimes to be considered.

Structural identifiability of surface binding reactions involving heterogeneous analyte: Application to surface plasmon resonance experiments

Binding affinities are useful measures of target interaction and have an important role in understanding biochemical reactions that involve binding mechanisms. Surface plasmon resonance (SPR) provides convenient real-time measurement of the reaction that enables subsequent estimation of the reaction constants necessary to determine binding affinity. Three models are considered for application to SPR experiments-the well-mixed Langmuir model and two models that represent the binding reaction in the presence of transport effects. One of these models, the effective rate constant approximation, can be derived from the other by applying a quasi-steady state assumption. Uniqueness of the reaction constants with respect to SPR measurements is considered via a structural identifiability analysis. It is shown that the models are structurally unidentifiable unless the sample concentration is known. The models are also considered for analytes with heterogeneity in the binding kinetics. This heterogeneity further confounds the identifiability of key parameters necessary for reliable estimation of the binding affinity.