Posttransplantation production of donor HLA-specific antibodies as a predictor of renal transplant outcome

BACKGROUND

This study aimed to determine whether the production, in renal transplant recipients, of antibodies directed against donor HLA mismatches is predictive of transplant failure.

METHODS

The failure study group comprised 112 adult recipients of primary renal transplants who had re-entered the transplant waiting list after failure of the first graft. A control group of 123 recipients with functioning transplants was selected from transplantations performed during the same time period, in which patients had equivalent HLA matching and immunosuppression and a minimum of 5 years of follow-up. Sera taken before transplantation and at 1, 3, and 6 months and annually after transplantation were tested by enzyme-linked immunoabsorbent assay (ELISA) for the presence of HLA class I- and class II-specific antibodies. Antibody specificity was defined by a combination of cytotoxicity, ELISA, and flow cytometry techniques to determine whether the antibodies were directed against donor mismatches.

RESULTS

All recipients were negative for donor HLA-specific antibodies before transplantation. After transplantation, 57 (50.9%) of the 112 patients in the failure group produced donor HLA-specific antibodies compared with 2 (1.6%) of the 123 controls (P<0.0001; odds ratio [OR]=64.98; confidence interval [CI], 14.78-399.51). For 60% of the donor-specific antibody-positive patients, antibodies were detected before transplant failure. In 17 cases, these were class I specific; in 14 cases, class II specific; and in 3 cases, specific for both class I and II.

CONCLUSIONS

This study has demonstrated that the production of posttransplantation antibodies directed against donor HLA-A, -B, -Cw, -DR, and -DQ mismatches are all strongly predictive of transplant failure.

Molecular architecture of the Goodpasture autoantigen in anti-GBM nephritis

BACKGROUND

In Goodpasture's disease, circulating autoantibodies bind to the noncollagenous-1 (NC1) domain of type IV collagen in the glomerular basement membrane (GBM). The specificity and molecular architecture of epitopes of tissue-bound autoantibodies are unknown. Alport's post-transplantation nephritis, which is mediated by alloantibodies against the GBM, occurs after kidney transplantation in some patients with Alport's syndrome. We compared the conformations of the antibody epitopes in Goodpasture's disease and Alport's post-transplantation nephritis with the intention of finding clues to the pathogenesis of anti-GBM glomerulonephritis.

METHODS

We used an enzyme-linked immunosorbent assay to determine the specificity of circulating autoantibodies and kidney-bound antibodies to NC1 domains. Circulating antibodies were analyzed in 57 patients with Goodpasture's disease, and kidney-bound antibodies were analyzed in 14 patients with Goodpasture's disease and 2 patients with Alport's post-transplantation nephritis. The molecular architecture of key epitope regions was deduced with the use of chimeric molecules and a three-dimensional model of the alpha345NC1 hexamer.

RESULTS

In patients with Goodpasture's disease, both autoantibodies to the alpha3NC1 monomer and antibodies to the alpha5NC1 monomer (and fewer to the alpha4NC1 monomer) were bound in the kidneys and lungs, indicating roles for the alpha3NC1 and alpha5NC1 monomers as autoantigens. High antibody titers at diagnosis of anti-GBM disease were associated with ultimate loss of renal function. The antibodies bound to distinct epitopes encompassing region E(A) in the alpha5NC1 monomer and regions E(A) and E(B) in the alpha3NC1 monomer, but they did not bind to the native cross-linked alpha345NC1 hexamer. In contrast, in patients with Alport's post-transplantation nephritis, alloantibodies bound to the E(A) region of the alpha5NC1 subunit in the intact hexamer, and binding decreased on dissociation.

CONCLUSIONS

The development of Goodpasture's disease may be considered an autoimmune "conformeropathy" that involves perturbation of the quaternary structure of the alpha345NC1 hexamer, inducing a pathogenic conformational change in the alpha3NC1 and alpha5NC1 subunits, which in turn elicits an autoimmune response. (Funded by the National Institute of Diabetes and Digestive and Kidney Diseases.)

MHC class I chain-related protein A antibodies and shedding are associated with the progression of multiple myeloma

Monoclonal gammopathy of undetermined significance (MGUS) is a common disorder of aging and a precursor lesion to full-blown multiple myeloma (MM). The mechanisms underlying the progression from MGUS to MM are incompletely understood but include the suppression of innate and adaptive antitumor immunity. Here, we demonstrate that NKG2D, an activating receptor on natural killer (NK) cells, CD8(+) T lymphocytes, and MHC class I chain-related protein A (MICA), an NKG2D ligand induced in malignant plasma cells through DNA damage, contribute to the pathogenesis of MGUS and MM. MICA expression is increased on plasma cells from MGUS patients compared with normal donors, whereas MM patients display intermediate MICA levels and a high expression of ERp5, a protein disulfide isomerase linked to MICA shedding (sMICA). MM, but not MGUS, patients harbor circulating sMICA, which triggers the down-regulation of NKG2D and impaired lymphocyte cytotoxicity. In contrast, MGUS, but not MM, patients generate high-titer anti-MICA antibodies that antagonize the suppressive effects of sMICA and stimulate dendritic cell cross-presentation of malignant plasma cells. Bortezomib, a proteasome inhibitor with anti-MM clinical efficacy, activates the DNA damage response to augment MICA expression in some MM cells, thereby enhancing their opsonization by anti-MICA antibodies. Together, these findings reveal that the alterations in the NKG2D pathway are associated with the progression from MGUS to MM and raise the possibility that anti-MICA monoclonal antibodies might prove therapeutic for these disorders.

Catalytic activity of antibodies against factor VIII in patients with hemophilia A

Hemophilia A is an X chromosome-linked recessive disorder resulting in defective or deficient factor VIII (FVIII) molecules, which, in its severe form, is a life-threatening and crippling hemorrhagic disease. Infusion of homologous FVIII to patients with severe hemophilia A results, in 25% of patients, in the emergence of alloantibodies against FVIII (inhibitors)( ref. 1) that inhibit FVIII procoagulant activity by steric hindrance of the interaction of FVIII either with stabilizing molecules, with molecules essential for its activity or with activating molecules. Here, we report on the proteolysis of FVIII by alloantibodies of two patients with severe hemophilia A, demonstrating a previously unknown mechanism by which FVIII inhibitors may prevent the pro-coagulant function of FVIII. The kinetic parameters of FVIII hydrolysis indicate a functional role for the catalytic immune response in the inactivation of FVIII in vivo. The characterization of alloantibodies against FVIII as site-specific proteases may provide new approaches to the treatment of FVIII inhibitors.

Suppression of HLA-specific alloantibodies by high-dose intravenous immunoglobulins (IVIg). A potential tool for transplantation of immunized patients

Renal transplantation in patients presenting end-stage renal failure can be hampered by the presence of alloantibodies against HLA antigens. In 4 out of 5 patients with HLA-specific alloantibodies waiting for a renal allograft, treatment with high-dose i.v. Ig resulted in a prolonged suppression (over 3 months) of most of the panel-reactive anti-HLA antibodies (PRA). Intravenous polyclonal human Ig (IVIg) and F(ab')2 fragments from IVIg inhibited the binding of patients' plasma and IgG fractions to peripheral blood lymphocytes from normal donors as well as their cytotoxicity, suggesting that the in vivo effect of IVIg was mediated by the presence, in the IVIg preparation, of anti-idiotypes directed against idiotypes borne on the anti-HLA antibodies. Thus, treatment with IVIg can be a valuable tool toward the transplantation of immunized patients.

Kidney transplants, antibodies and rejection: is C4d a magic marker?

The immunohistochemical detection of the complement degradation product C4d in renal allograft biopsies has gained considerable clinical interest in recent years. The accumulation of C4d along peritubular capillaries is generally regarded as a marker for an antibody-mediated allo-response and is associated with poor graft survival. The aim of this review is to discuss histological findings associated with the deposition of C4d. Emphasis is placed on diagnostic and therapeutic implications. Unanswered questions regarding C4d and graft injury are highlighted.

Comparison of quadruple immunosuppression after liver transplantation with ATG or IL-2 receptor antibody

Treatment with monoclonal IL-2 receptor antibodies has been successfully used for immunosuppressive induction therapy following organ transplantation in the recent past. The present study was conducted to compare for the first time a cyclosporine-based quadruple immunosuppressive regimen including a monoclonal IL-2 receptor antibody or ATG as induction therapy after orthotopic liver transplantation. In two groups of 33 patients each, postoperative survival, graft biopsies, liver function enzymes, and the clinical courses after OLT were evaluated. Our results indicate that monoclonal IL-2 receptor antibody therapy as part of a quadruple immunosuppressive regimen is better tolerated and is at least as effective as ATG in prevention of allograft rejection following OLT. Furthermore, our data indicate that a slightly better liver function in general and a lower incidence of rejection reactions necessitating treatment could be observed in the group of patients treated with the monoclonal IL-2 receptor antibody. This study provides evidence that monoclonal IL-2 receptor antibody therapy may be a useful tool for the immunosuppressive induction therapy following clinical orthotopic liver transplantation.

The prevalence of proteolytic antibodies against factor VIII in hemophilia A

BACKGROUND

Factor VIII inhibitors are IgG alloantibodies that arise during replacement therapy in 25 to 50 percent of patients with severe hemophilia A. The hydrolysis of factor VIII by anti--factor VIII antibodies has been proposed as a mechanism of inactivation of factor VIII.

METHODS

We purified IgG from patients with severe hemophilia A. The proteolytic activity of the antibodies was assessed by incubating the IgG with biotinylated human factor VIII and analyzing patterns of factor VIII cleavage by sodium dodecyl sulfate--polyacrylamide-gel electrophoresis and immunoblotting. The controls were normal human IgG and IgG purified from plasma of patients with hemophilia who did not have inhibitory antibodies.

RESULTS

Significant proteolytic activity was detected in IgG from 13 of 24 inhibitor-positive patients. No hydrolytic activity was detected in control antibodies of IgG from patients without inhibitors. The rate of hydrolysis of factor VIII by purified IgG correlated positively with the factor VIII--neutralizing activity of IgG in plasma (r2=0.67, P=0.029). Principal-component analysis of migration profiles of digestion fragments demonstrated the heterogeneity of the catalytic potential of factor VIII inhibitors among patients.

CONCLUSIONS

Proteolysis is a mechanism by which IgG antibodies against factor VIII can inactivate factor VIII.

Antibodies to basement membrane heparan sulfate proteoglycans bind to the laminae rarae of the glomerular basement membrane (GBM) and induce subepithelial GBM thickening

Antibodies specific for the core protein of basement membrane HSPG (Mr = 130,000) were administered to rats by intravenous injection, and the pathologic consequences on the kidney were determined at 3 min to 2 mo postinjection. Controls were given antibodies against gp330 (the pathogenic antigen of Heymann nephritis) or normal rabbit IgG. The injected anti-HSPG(GBM) IgG disappeared rapidly (by 1 d) from the circulation. The urinary excretion of albumin increased in a dose-dependent manner during the first 4 d, was increased 10-fold at 1-2 mo, but remained moderate (mean = 12 mg/24 h). By immunofluorescence the anti-HSPG(GBM) was seen to bind rapidly (by 3 min) to all glomerular capillaries, and by immunoperoxidase staining the anti-HSPG was seen to bind exclusively to the laminae rarae of the GBM where it remained during the entire 2-mo observation period. C3 was detected in glomeruli immediately after the injection (3 min), where it bound exclusively to the lamina rara interna; the amount of C3 bound increased up to 2 h but decreased rapidly thereafter, and was not detectable after 4 d. Mononuclear and PMN leukocytes accumulated in glomerular capillaries, adhered to the capillary wall, and extended pseudopodia through the endothelial fenestrae to contact in the LRI of the GBM where the immune deposits and C3 were located. At 1 wk postinjection, staining for C3 reappeared in the glomeruli of some of the rats, and by this time most of the rats, including controls injected with normal rabbit IgG, had circulating anti-rabbit IgG (by ELISA) and linear deposits of rat IgG along the GBM (by immunofluorescence). Beginning at 9 d, there was progressive subepithelial thickening of the GBM which in some places was two to three times its normal width. This thickening was due to the laying down of a new layer of basement membrane-like material on the epithelial side of the GBM, which gradually displaced the old basement membrane layers toward the endothelium. The results show that the core proteins of this population of basement membrane HSPG (Mr = 130,000), which are ubiquitous components of basement membranes, are exposed to the circulation and can bind anti-HSPG(GBM) IgG in the laminae rarae of the GBM. Binding of these antibodies to the GBM leads to changes (C3 deposition, leukocyte adherence, moderate proteinuria, GBM thickening) considered typical of the acute phase of anti-GBM glomerulonephritis. Antibody binding interferes with the normal turnover of the GBM, presumably by affecting the biosynthesis and/or degradation of basement membrane components.

Analysis of fluorescence lifetime and quenching of FITC-conjugated antibodies on cells by phase-sensitive flow cytometry

Fluorescent antibodies are often used to measure the number of receptor sites on cells. The quantitative estimate of the number of receptor sites using this procedure assumes that the fluorescence intensity on a cell is proportional to the number of bound antibodies. Quenching may invalidate this assumption. For many fluorophores, intermolecular interactions and energy transfer between molecules in close proximity to one another results in self-quenching. This effect can occur in antibody probes with a high fluorochrome to protein (F/P) ratio. It can also occur due to close proximity antibodies relative to one another on a highly labeled cell surface. Since self-quenching is accompanied by a change in the fluorescence decay and a decrease in the fluorescence lifetime, it may be conveniently identified using fluorescence lifetime spectroscopy. In this paper we apply the phase-sensitive detection method to investigate the impact of self-quenching on fluorescence lifetimes by flow cytometry, using a model system consisting of FITC conjugated anti-mouse Thy1.2 antibodies bound to murine thymus cells. We show that in addition to the expected variation of lifetimes as a function of F/P ratio of the probes, the fluorescence lifetime diminishes also as a function of antibody labeling concentration on the cell surface. This is consistent with self-quenching effects expected at high densities of FITC molecules.

Panel of reactive T cells as a measurement of primed cellular alloimmunity in kidney transplant candidates

Pretransplantation panel reactive antibody (PRA) testing assesses posttransplantation risk for antibody-mediated graft injury. It was postulated analogously that screening for effector/memory alloreactive T cells by "panel of reactive T cells" (PRT) using IFN-gamma enzyme-linked immunosorbent spot assays would evaluate independently cellular alloimmunity in transplant candidates. Peripheral blood lymphocytes from 41 hemodialysis patients who were awaiting first renal transplants were tested against a panel of allogeneic stimulator cells. Positive assays were defined arbitrarily as >25 spots/300,000 peripheral blood lymphocytes, and positive PRT was defined as when the responder reacted to 40 or 75% (PRT-75) of the stimulators. Seventeen percent of patients were PRT-75+, whereas 32% were PRA+. Twelve percent of the cohort was PRT-75+/PRA-, and only 5% of the patients were PRA+/PRT-75+, indicating that T cell alloreactivity did not routinely imply B cell sensitization and vice versa. PRT-75+ patients were more likely to be younger (<55 yr) and black. In contrast, a positive PRA was significantly associated with female gender but not race or age. Pretransplantation screening of cellular alloimmunity by enzyme-linked immunosorbent spot-based PRT detects a subset of hemodialysis patients who differ from those that are PRA+. Preliminary correlations with posttransplantation outcome in seven recipients suggest that PRT screening has the potential to aid in risk assessment in renal transplant candidates.

C4d Deposition in Cardiac Allografts Correlates With Alloantibody

BACKGROUND

The presence of C4d along the peritubular capillaries in kidney allografts correlates with the presence of anti-donor serum alloantibodies. We applied C4d staining to cardiac allograft and non-allograft biopsies to determine if C4d staining in heart allografts correlates with anti-donor serum alloantibodies.

METHODS

We stained for C4d all available frozen tissue biopsies from cardiac transplant recipients between 1997 and 2002, including autopsies. Two hundred twenty-one tissue samples from 124 patients were analyzed. Included in both groups were a variety of International Society for Heart and Lung Transplantation (ISHLT) grades of rejection plus post-implant cardiac ischemic injury (PIMI), and biopsies from patients who had received OKT3. Patients were matched by age, gender and interval after transplantation. Forty-four additional controls were included from patients biopsied for non-transplant-related cardiac disease.

RESULTS

C4d staining of the myocardial capillaries correlated well with the presence of anti-donor alloantibodies. Twenty-one of 25 biopsies from patients with anti-donor alloantibodies showed C4d staining (84%), whereas only 7 of 60 without anti-donor alloantibodies stained for C4d. C4d staining did not correlate with ischemia or OKT3 therapy. Only 4 of 44 non-transplant biopsies stained for C4d (9%). An example of the clinical utility of C4d staining in patient care is presented.

CONCLUSIONS

C4d staining of the capillaries in cardiac allografts correlates well with anti-donor serum alloantibodies, is a useful assay to verify alloantibody deposition, and can be used to establish one of the criteria for antibody-mediated cardiac rejections.

Identification of dialysis patients with panel-reactive memory T cells before kidney transplantation using an allogeneic cell bank

Donor-reactive cellular sensitization does not routinely suggest humoral sensitization and vice versa, but both predict poor kidney transplant outcome. Irrespective of donor reactivity, panel-reactive antibody (PRA) screening identifies patients who are at enhanced risk. Therefore, it was hypothesized that panel-reactive memory T cell reactivity (PRT) might be an additional risk assessment factor of dialysis patients who are on the transplant waiting list. IFN-gamma-enzyme-linked immunosorbent spot memory T cell frequencies were determined in 10 healthy volunteers and 41 hemodialysis patients using for stimulation an allogeneic cell bank (ACB) from 17 healthy individuals who represented the most frequent white HLA antigens. Positive responses to ACB were analogous to PRA defined as percentage of positive assays of the ACB sets. Hemodialysis patients expressed higher PRT levels compared with healthy volunteers. Five of 10 PRT++ patients were PRA negative, and only four of 10 PRA++ patients exhibited PRT reactivity, suggesting independence of humoral and cellular sensitization. Pretransplantation PRT testing of recipients might improve individual risk assessment to make individualized therapy decisions.

Relative antithrombotic effect of soluble GPVI dimer compared with anti-GPVI antibodies in mice

Glycoprotein VI (GPVI) is an essential platelet collagen receptor; therefore, the inhibition of GPVI-collagen interactions may be an attractive antithrombotic strategy. We have previously shown that targeting of GPVI with antibodies leads to the depletion of the receptor and to long-term antithrombotic protection in mice. An alternative agent to interfere with GPVI-collagen interactions might be soluble GPVI acting as a competitive inhibitor, thereby averting undesired effects on platelets. To test this, we expressed soluble dimeric human GPVI, comprising the extracellular domain of the receptor fused to the human immunoglobulin Fc domain (GPVI-Fc), and compared its antithrombotic potential with that of anti-GPVI antibodies in mice. In contrast to a recent report, we found by intravital fluorescence microscopy and ultrasonic flow measurements that GPVI-Fc had no effect on platelet adhesion and thrombus formation at the injured arterial wall, whereas anti-GPVI antibodies profoundly inhibited these processes. Similar results were obtained with a fusion protein comprising the extracellular domain of mouse GPVI and human IgG-Fc. This indicates that direct targeting of GPVI provides significantly stronger protection against arterial thrombosis than soluble GPVI dimer.

Characterization of murine immunoglobulin G antibodies against human amyloid-beta1-42

It has been demonstrated that immunization of transgenic mouse models of Alzheimer's disease (AD) with amyloid-beta1-42 peptide (Abeta1-42) results in amelioration of AD-like pathology, including reduced soluble and deposited beta-amyloid and decreased cognitive impairment. Based on the proposed importance of immunoglobulin G (IgG) anti-Abeta antibodies (Abs) in these effects, we sought to characterize these Abs in splenocytes from mice immunized with Abeta1-42. Data show that a more aggregated preparation of Abeta1-42 gives a robust IgG anti-Abeta Ab response, while these Abs are almost undetectable when a less aggregated preparation of Abeta1-42 is used as the immunogen. Importantly, IgG anti-Abeta Ab production is detected after just 12 weeks of Abeta1-42 treatment. Analysis of anti-Abeta Ab IgG isotypes reveals that the majority of these Abs are IgG1, with significantly fewer Abs of the IgG2a or IgG2b isotypes (IgG1>IgG2a>IgG2b), suggesting a T lymphocyte helper type II response after Abeta1-42 immunization. To determine the epitope of Abeta recognized by IgG anti-Abeta Abs, intact Abeta and Abeta peptide fragments were analyzed for their ability to bind these Abs. Data show that these Abs specifically recognize an amino-terminal epitope of Abeta between amino acids one and twelve, with higher affinity for a more soluble preparation of Abeta1-42. These data further indicate the immunogenic potential of Abeta1-42 and offer insight into the nature of the IgG anti-Abeta Ab response.

Common inhibitory effects of human anti-C2 domain inhibitor alloantibodies on factor VIII binding to von Willebrand factor

Factor VIII (FVIII) inhibitor alloantibodies obtained from seven severe haemophilia A patients were examined for their binding regions and their effects on FVIII binding to von Willebrand factor (vWF). Immunoblotting analysis with a panel of recombinant fragments demonstrated that the binding regions of antibodies in cases 1-5 were contained in the C2 domain of the light chain. Antibodies from cases 1 and 2, which recognized an epitope within residues 2248-2312, completely inhibited FVIII/vWF binding in an ELISA (IC50: 5.0 and 9.0 micrograms/ml, respectively). Antibodies from case 3 recognizing 2170-2312 and case 5 recognizing 2170-2327 also inhibited FVIII/vWF binding (IC50: 110 and 400 micrograms/ml, respectively). Case 4 antibodies recognizing 2218-2307 showed barely detectable inhibition and cases 6 and 7 antibodies recognizing the 44 kD heavy chain, did not inhibit. Our results demonstrate that all anti-C2 alloantibodies with epitopes that extend to the residue 2312 inhibit vWF binding and that an overlap of the inhibitor epitope with residues 2308-2312 is critical for maximal inhibition of vWF binding. Prevention of FVIII/vWF binding appears to be a common property of anti-C2 domain inhibitor alloantibodies.

Direct electrical detection of antigen–antibody binding on diamond and silicon substrates using electrical impedance spectroscopy

The integration of biological molecules with semiconducting materials such as silicon and diamond has great potential for the development of new types of bioelectronic devices, such as biosensors and bioactuators. We have investigated the electrical properties of the antibody-antigen modified diamond and silicon surfaces using electrical impedance spectroscopy (EIS). Frequency dependent measurements at the open-circuit potential show: (a) significant changes in impedance at frequency >10(4) Hz when the surface immobilized IgG was exposed to anti-IgG, and (b) only little or no change when exposed to anti-IgM. Mott-Schottky measurements at high frequency (200 kHz) show that the impedance is dominated by the space charge layer of the semiconducting substrates. Silicon surfaces modified in a similar manner to the diamond surface are compared; n-type and p-type samples show complementary behavior, as expected for a field effect. We also show it is possible to directly observe antigen-antibody interaction at a fixed frequency in real time, and with no additional labeling.

Antibody-Mediated Rejection of Cardiac Allografts in CCR5-Deficient Recipients

Rejected MHC-mismatched cardiac allografts in CCR5(-/-) recipients have low T cell infiltration, but intense deposition of C3d in the large vessels and capillaries of the graft, characteristics of Ab-mediated rejection. The roles of donor-specific Ab and CD4 and CD8 T cell responses in the rejection of complete MHC-mismatched heart grafts by CCR5(-/-) recipients were directly investigated. Wild-type C57BL/6 and B6.CCR5(-/-) (H-2(b)) recipients of A/J (H-2(a)) cardiac allografts had equivalent numbers of donor-reactive CD4 T cells producing IFN-gamma, whereas CD4 T cells producing IL-4 were increased in CCR5(-/-) recipients. Numbers of donor-reactive CD8 T cells producing IFN-gamma were reduced 60% in CCR5(-/-) recipients. Day 8 posttransplant serum titers of donor-specific Ab were 15- to 25-fold higher in CCR5(-/-) allograft recipients, and transfer of this serum provoked cardiac allograft rejection in RAG-1(-/-) recipients within 14 days, whereas transfer of either serum from wild-type recipients or immune serum from CCR5-deficient recipients diluted to titers observed in wild-type recipients did not mediate this rejection. Wild-type C57BL/6 and B6.CCR5(-/-) recipients rejected A/J cardiac grafts by day 11, whereas rejection was delayed (day 12-60, mean 21 days) in muMT(-/-)/CCR5(-/-) recipients. These results indicate that the donor-specific Ab produced in CCR5(-/-) heart allograft recipients is sufficient to directly mediate graft rejection, and the absence of recipient CCR5 expression has differential effects on the priming of alloreactive CD4 and CD8 T cells.

Interactions of IgM ABO antibodies and complement with methoxy-PEG-modified human RBCs

BACKGROUND

RBCs modified with cyanuric chloride activated methoxy-PEG (CmPEG; 5000 Da) are less immunogenic than untreated RBCs, and their use thus may reduce the risk of alloimmunization in chronically transfused patients.

STUDY DESIGN AND METHODS

To further examine the potential utility of CmPEG-RBCs, the effects of derivatization on an arm of the immune system that plays an important role in transfusion rejection-the complement system--were determined.

RESULTS

When CmPEG-RBCs were incubated in autologous or heterologous ABO-matched serum, no classical or alternative pathway consumption was found, no C3a was generated, no cell-bound C3b or C9 was detected, and no cell lysis occurred. Cell-bound complement regulation was normal for CmPEG-RBCs, as determined by acidified serum or reactive lysis assays. CmPEG-RBCs differed from control RBCs only when incubated in ABO-mismatched serum. In that case, CmPEG modification failed to protect against ABO antibody-dependent complement-mediated lysis. Indeed, cell lysis was actually enhanced at CmPEG concentrations >1.0 mM.

CONCLUSION

The enhanced lysis of CmPEG-RBCs in ABO-mismatched serum correlated with increased IgM binding and C3a generation and elevated C3b and C9 membrane deposition. While PEG modification effectively blocks non-ABO antigens, these data show that ABO matching is still required. Once ABO-matched, these modified RBCs retain great potential for the prevention of alloimmunization.

C6 produced by macrophages contributes to cardiac allograft rejection

The terminal components of complement C5b-C9 can cause significant injury to cardiac allografts. Using C6-deficient rats, we have found that the rejection of major histocompatibility (MHC) class I-incompatible PVG.R8 (RT1.A(a)B(u)) cardiac allografts by PVG.1U (RT1.A(u)B(u)) recipients is particularly dependent on C6. This model was selected to determine whether tissue injury results from C6 produced by macrophages, which are a conspicuous component of infiltrates in rejecting transplants. We demonstrated that high levels of C6 mRNA are expressed in isolated populations of macrophages. The relevance of macrophage-produced C6 to cardiac allograft injury was investigated by transplanting hearts from PVG. R8 (C6-) donors to PVG.1U (C6-) rats which had been reconstituted with bone marrow from PVG.1U (C6+) rats as the sole source of C6. Hearts grafted to hosts after C6 reconstitution by bone marrow transplantation underwent rejection characterized by deposition of IgG and complement on the vascular endothelium together with extensive intravascular aggregates of P-selectin-positive platelets. At the time of acute rejection, the cardiac allografts contained extensive perivascular and interstitial macrophage infiltrates. RT-PCR and in situ hybridization demonstrated high levels of C6 mRNA in the macrophage-laden transplants. C6 protein levels were also increased in the circulation during rejection. To determine the relative contribution to cardiac allograft rejection of the low levels of circulating C6 produced systemically by macrophages, C6 containing serum was passively transferred to PVG.1U (C6-) recipients of PVG.R8 (C6-) hearts. This reconstituted the C6 levels to about 3 to 6% of normal values, but failed to induce allograft rejection. In control PVG.1U (C6-) recipients that were reconstituted with bone marrow from PVG.1U (C6-) donors, C6 levels remained undetectable and PVG.R8 cardiac allografts were not rejected. These results indicate that C6 produced by macrophages can cause significant tissue damage.

Antibodies that define NANA-independent MN-system antigens

The hemagglutinating properties of a large proportion of anti-M and anti-N reagents, and sera containing antibodies to MN-related antigens, have been shown to be unaffected by treatment of red blood cells with neuraminidase. These antibodies, which define NANA-independent MN-system structures, provide further evidence that MN blood group specificity may also be determined by moieties other than N-acetylneuraminic acid.

A novel method of cell separation based on dual parameter immunomagnetic cell selection

We describe a novel method of cell purification involving two stage immunomagnetic selection which permits isolation of cells based on a second cell surface marker without the need for removal of beads used in the first selection step. This approach takes advantage of the size differences between commercially available immunomagnetic beads and/or particles and their differing properties in terms of attraction to magnetic fields of various strengths. The first stage of separation involves positive selection of cells using the Miltenyi MiniMacs system, utilising 50 nm MicroBeads and a MiniMacs magnet. Cells obtained from this procedure--still rosetted with 50 nm MicroBeads--can then be subjected to further positive or negative selection using either streptavidin M280 or anti-rat M450 Dynabeads, without the need for prior bead removal, since the strength of the magnetic field of the Dynal separator is sufficient to attract the larger Dynabeads but not the MicroBeads. Here, we show that this system can be used to isolate a number of cell types including very rare target cell populations such as haemopoietic stem cells, using two different surface markers without perturbing subsequent functional capacity.

The generation and characterization of potentially therapeutic Abeta antibodies in mice: differences according to strain and immunization protocol

Previous studies have shown that in various mouse models of Alzheimer's disease (AD), amyloid beta-protein (Abeta) antibodies generated by Abeta peptide immunization resulted in the prevention of Abeta plaque formation in brains of young mice, decreased Abeta plaque burdens in older mice and improved cognition. The purpose of this study was to optimize Abeta immunization protocols for future trials in transgenic mouse models of AD. The timing and titers of Abeta antibody production, as well as epitope(s) and imunoglobulin isotypes, were compared between two different mouse strains (C57BL/6 and B6D2F1) and five treatment protocols: (1). chronic Abeta nasal administration, (2). repeated Abeta intraperitoneal (i.p.) injection, (3). one i.p. injection followed by chronic Abeta nasal administration, (4). chronic and concurrent Abeta nasal administration + Abeta i.p. injection, and (5). untreated controls. B6D2F1 mice generated Abeta antibodies earlier and in higher quantities than the C57BL/6 mice, indicating that B6D2F1 mice are more responsive to Abeta immunization. For both strains, mice that received the combination of Abeta nasal + Abeta i.p. injection showed the highest antibody titers. Epitope mapping experiments indicated that the mouse anti-Abeta antibodies recognize residues within Abeta1-15. Immunoglobulin isotyping demonstrated that the Abeta antibodies are of the Th-2 anti-inflammatory type, IgG1 and IgG2b, with a few IgM. Currently there is no effective therapy for Alzheimer's disease; thus if Abeta immunization proves effective, it would be a significant step in the prevention and/or treatment of this devastating disease.

Half-lives of two types of rat homocytotropic antibodies in circulation and in the skin

The half-lives of two classes of rat immunoglobulins with homocytotropic properties, i.e., IgE and IgG2a, in the circulating blood and in the skin were studied. The catabolism of both normal (reaginic) and pathological (myeloma) IgE proteins in circulation was found to be extremely rapid with a half-life of 12 h. In contrast, the half-life of IgE antibody in the homologous skin was calculated to be 7.4 days. On the other hand, the half-life of IgG2a in circulation was about 5 days regardless of normal or pathological origin. IgG2a protein was, however, rapidly cleared from the injected skin site with a half life of 2.4 days, a value not longer than that obtained with nonskin-sensitizing goat IgG. The results indicate that rat IgE has an extremely short half-life in circulation despite of its sensitization period in tissues, and that the affinity for the target cells, as well as the mode of sensitization, of the two classes of homocytotropic antibodies, IgE and IgG2a, is different.