IgG Donor-Specific Anti-Human HLA Antibody Subclasses and Kidney Allograft Antibody-Mediated Injury

Antibodies may have different pathogenicities according to IgG subclass. We investigated the association between IgG subclasses of circulating anti-human HLA antibodies and antibody-mediated kidney allograft injury. Among 635 consecutive kidney transplantations performed between 2008 and 2010, we enrolled 125 patients with donor-specific anti-human HLA antibodies (DSA) detected in the first year post-transplant. We assessed DSA characteristics, including specificity, HLA class specificity, mean fluorescence intensity (MFI), C1q-binding, and IgG subclass, and graft injury phenotype at the time of sera evaluation. Overall, 51 (40.8%) patients had acute antibody-mediated rejection (aABMR), 36 (28.8%) patients had subclinical ABMR (sABMR), and 38 (30.4%) patients were ABMR-free. The MFI of the immunodominant DSA (iDSA, the DSA with the highest MFI level) was 6724±464, and 41.6% of patients had iDSA showing C1q positivity. The distribution of iDSA IgG1–4 subclasses among the population was 75.2%, 44.0%, 28.0%, and 26.4%, respectively. An unsupervised principal component analysis integrating iDSA IgG subclasses revealed aABMR was mainly driven by IgG3 iDSA, whereas sABMR was driven by IgG4 iDSA. IgG3 iDSA was associated with a shorter time to rejection (P<0.001), increased microcirculation injury (P=0.002), and C4d capillary deposition (P<0.001). IgG4 iDSA was associated with later allograft injury with increased allograft glomerulopathy and interstitial fibrosis/tubular atrophy lesions (P<0.001 for all comparisons). Integrating iDSA HLA class specificity, MFI level, C1q-binding status, and IgG subclasses in a Cox survival model revealed IgG3 iDSA and C1q-binding iDSA were strongly and independently associated with allograft failure. These results suggest IgG iDSA subclasses identify distinct phenotypes of kidney allograft antibody-mediated injury.     

Therapeutic potential of monoclonal antibodies to the leukocyte-common antigen. Synergy and interference in complement-mediated lysis

A series of rat monoclonal antibodies against the human leukocyte-common antigen were isolated and, by means of competitive binding assays with purified antigen, two distinct groups were defined that recognize different epitopes of the molecule. None of these antibodies were lytic with human complement, but when antibodies against each of these two epitopes were used in combination, synergistic lysis with human complement could be obtained. Synergistic lysis was only seen when each antibody of the pair was of the IgG2b subclass. IgG2a antibodies could not synergize, and in fact could interfere with lysis obtained by the pair of IgG2b antibodies. Although synergy has so far only been studied for rat monoclonal antibodies we also show that it is possible with mouse antibodies or with combinations of mouse and rat antibodies. The information about the principles of synergy and its interference should provide a rationale for using well-planned cocktails of monoclonal antibodies for therapy rather than a shotgun polyclonal antiserum.     

Donor‐specific HLA antibodies: evaluating the risk for graft loss in renal transplant recipients with isotype switch from complement fixing IgG1/IgG3 to noncomplement fixing IgG2/IgG4 anti‐HLA alloantibodies

Human leukocyte antigen alloantibodies have a multitude of damaging effects on the allograft, both complement (C′) activation and Fc‐independent ones. To date, the clinical significance of non‐C′ fixing (NCF) HLA donor‐specific antibodies (DSA) is still unclear. In this study, we investigated whether renal transplant recipients with NCF‐DSA subclasses (IgG2/IgG4, IgA1/IgA2) are at higher risk of graft loss compared to patients with exclusively C′ fixing (IgG1/IgG3). Blood samples from 274 patients were analyzed for HLA IgG and IgA subclasses using a modified single‐antigen bead assay. We identified 50 (18.2%) patients with circulating NCF antibodies either DSA (n = 17) or against third‐party HLA (n = 33). NCF‐DSAs were preferentially of IgG2/IgG4 isotype (11/17) and were mainly directed against HLA class II (13/17). NCF DSA were present as a mixture with strong C′ fixing IgG1/IgG3. Graft survival was similar between patients with exclusively C′ fixing antibodies and those with a mixture panel (log rang test P = 0.162), and also among patients with different immunoglobulin isotype and subclasses (long‐rank test, P = 0.732). We conclude that expansion of DSA to NCF subclasses postrenal transplantation does not seem to be associated with worse graft survival as compared to the presence of exclusive C′ fixing subclasses.     

Value of C3d assay and IgG subclass in the prediction of the flow cytometry cross-match result for renal transplantation

The aim of this study is to compare the association and the predictive capacity of DSA MFI, complement fixing capacity (C3d assay) and IgG subclasses determination in the prediction of FCxM result.MethodsWe used cryopreserved (70C) sera from potential renal transplant recipients, containing DSA against their respective potential donors. All patients showed negative AHG-CDC CxM and either positive or negative FCxM. Class I and Class II HLA-DSA were determined by Luminex SAB. C3d were detected by Luminex (Lifecodes®Immucor), DSA IgG 1–4 subclasses were evaluated using monoclonal antibodies specific for IgG subclasses (Luminex).Results93 donor/recipient tests were evaluated; 32 (35.9%) patients presented at least one C3d + Ab, of which only 11 (11.8%) were donor specific. At least one IgG subclass was identified in 45 samples (48.3%). Twenty-seven FCxM tests (29%) were positive. On multivariate analysis HLA mismatches, the IgG subclass detection, DSA MFI and class II PRA remain associated to FCxM whereas C3d + Ab was not associated. For the FCxM prediction, the IgG subclass detection in combination with the DSA-MFI > 2800, had the best negative predictive value 93.9 (CI 95%, 84.2–100).ConclusionNeither the C3d assay nor the IgG subclasses detection alone had an adequate predictive capacity for the FCxM. In the absence of IgG subclass detection and DSA-MFI < 2000, the probability of a negative FCxM was near 94%.     

High nephritogenicity of monoclonal antibodies belonging to IgG2a and IgG2b subclasses in rat anti-GBM nephritis

BACKGROUND: To examine a subclass-effect relationship and a dose-effect relationship of autoantibodies in the rat antiglomerular basement membrane (GBM) antibody-induced glomerulonephritis (anti-GBM nephritis) model, we injected homologous monoclonal antibodies against the NC1 domains of rat type IV collagen into inbred Wistar-Kyoto (WKY) rats. METHODS: Eight different autoantibodies from each of the IgG1, IgG2a, and IgG2b subclasses were established and administered to groups of four WKY rats at a dose of 300 microg/rat. To examine the dose-effect relationship, we administered 0 to 300 microg/rat of autoantibodies from each subclass to rats. RESULTS: All IgG1 antibodies induced mild nephritis, whereas the IgG2a and IgG2b antibodies induced moderate to severe nephritis. Some IgG2a and IgG2b antibodies induced pulmonary hemorrhage as well. These antibodies were reactive with alpha3(IV)NC1, alpha4(IV)NC1, or alpha5(IV)NC1. The minimum dose of antibody required to induce nephritis was 30 microg/rat for IgG1, 3 microg/rat for IgG2a, and 1 microg/rat for IgG2b. At doses of 30 microg/rat or less, antibody deposition was generally restricted to the GBM. At doses of 100 microg/rat or greater, antibody deposition extended to both the GBM and tubular basement membrane (TBM). Pulmonary hemorrhage was observed only when a large amount of pulmonary hemorrhagic antibody was administered. CONCLUSION: The severity of nephritis was dependent on both subclass and dose of autoantibodies. It becomes clear that pulmonary hemorrhage in anti-GBM nephritis is induced by autoantibodies.     

Monocyte Recruitment by HLA IgG‐Activated Endothelium: The Relationship Between IgG Subclass and FcγRIIa Polymorphisms

It is currently unclear which donor specific HLA antibodies confer the highest risk of antibody‐mediated rejection (AMR) and allograft loss. In this study, we hypothesized that two distinct features (HLA IgG subclass and Fcγ receptor [FcγR] polymorphisms) which vary from patient to patient, influence the process of monocyte trafficking to and macrophage accumulation in the allograft during AMR in an interrelated fashion. Here, we investigated the contribution of human IgG subclass and FcγR polymorphisms in monocyte recruitment in vitro by primary human aortic endothelium activated with chimeric anti‐HLA I human IgG1 and IgG2. Both subclasses triggered monocyte adhesion to endothelial cells, via a two‐step process. First, HLA I crosslinking by antibodies stimulated upregulation of P‐selectin on endothelium irrespective of IgG subclass. P‐selectin‐induced monocyte adhesion was enhanced by secondary interactions of IgG with FcγRs, which was highly dependent upon subclass. IgG1 was more potent than IgG2 through differential engagement of FcγRs. Monocytes homozygous for FcγRIIa‐H131 adhered more readily to HLA antibody‐activated endothelium compared with FcγRIIa‐R131 homozygous. Finally, direct modification of HLA I antibodies with immunomodulatory enzymes EndoS and IdeS dampened recruitment by eliminating antibody‐FcγR binding, an approach that may have clinical utility in reducing AMR and other forms of antibody‐induced inflammation.     

Determinants of the complement-fixing ability of recipient presensitization against HLA antigens

BACKGROUND: The presence of preformed alloantibodies with the ability to activate complement may pose a particular risk for kidney allograft rejection. The aim of this study was to evaluate variables that determine the complement-fixing capability of human leukocyte antigen (HLA) sensitization. METHODS: Sixty-five sensitized patients with > or =10% pretransplant panel-reactive antibody (PRA) levels uncovered by immunoglobulin G [IgG]FlowPRA HLA class I and/or class II screening were included. Applying modified FlowPRA screening, sera were evaluated for patterns of alloreactive IgG subclasses and IgM, and, in parallel, for their complement-activating ability assessed by flow cytometric detection of human complement split product deposition ([C4d]FlowPRA). RESULTS: Approximately two-thirds (68%) of tested sera were found to contain complement-fixing alloreactivity (> or =10%[C4d]FlowPRA). IgG1 type panel reactivity was predominant (detectable HLA class I and II reactivity in 93% and 91% of IgG-positive sera), followed by IgG3 (49%/44%), IgG2 (44%/27%), and IgG4 (19%/11%). Applying partial correlation we found an independent correlation of both %[IgG1]FlowPRA and %[IgG3]FlowPRA with %[C4d]FlowPRA reactivities (P< or =0.01). In addition, for IgG1 a contribution of the amount of bound alloantibody to complement-fixation was observed. Complement-fixation was also favored by the simultaneous presence of alloreactive IgG1, IgG3, and IgM. Previous grafting, but not pregnancy and transfusion, was independently associated with complement-fixing sensitization (P<0.05), presumably due to increased IgG1 type reactivity. CONCLUSIONS: Anti-HLA antibody-triggered complement activation is dependent on both the pattern of Ig reactivities and the amount of bound antibody. Previous transplantation represents a major risk factor for the development of complement-fixing sensitization.     

Donor-specific human leukocyte antigen antibodies of the immunoglobulin G3 subclass are associated with chronic rejection and graft loss after liver transplantation

In a previous study, we found that 92% of patients with chronic rejection had donor-specific human leukocyte antigen antibodies (DSAs), but surprisingly, 61% of comparator patients without rejection also had DSAs. We hypothesized that immunoglobulin G (IgG) subclasses were differentially distributed between the 2 groups. A modified single-antigen bead assay was used to detect the presence of individual IgG subclasses against human leukocyte antigen in 39 chronic rejection patients and 66 comparator patients. DSAs of the IgG1 subclass were most common and were found in 45% of all patients; they were followed by IgG3 DSAs (21%), IgG4 DSAs (14%), and IgG2 DSAs (13%). The percentage of patients with multiple IgG subclasses was significantly higher in the chronic rejection group versus the comparator group (50% versus 14%, P < 0.001). Patients with normal graft function in the presence of DSAs mostly had isolated IgG1, whereas patients with chronic rejection had a combination of IgG subclasses. Patients who developed DSAs of the IgG3 subclass showed an increased risk of graft loss (hazard ratio = 3.35, 95% confidence interval = 1.39-8.05) in comparison with patients with DSAs of other IgG subclasses or without DSAs. Although further study is needed, the determination of the IgG subclass in DSA-positive patients may help us to identify patients with a higher risk of chronic rejection and graft loss.     

Characterization of natural human anti-non-gal antibodies and their effect on activation of porcine gal-deficient endothelial cells

BACKGROUND: The generation of Galalpha1-3Gal (Gal) transferase deficient pigs has increased the interest in non-Gal antigens potentially representing important targets for xenoreactive antibody binding leading to xenograft rejection. The present study addressed the levels and immunoglobulin isotypes of preformed human anti-non-Gal antibodies and their potential to activate porcine endothelial cells. METHODS: Porcine endothelial cells lacking the Gal epitope (Gal-/-) were used to measure immunoglobulin (Ig) M and IgG subclass anti-non-Gal antibodies, using sera from 80 blood donors and pooled human AB serum. Antibodies specific for the non-Gal Hanganutziu-Deicher (HD) xenoantigen were measured by enzyme-linked immunosorbent assay. Activation of Gal-/- and Gal+/+ endothelial cells by human serum was measured, in the presence or absence of complement inhibitors, by E-selectin cell-surface expression using flow cytometry. RESULTS: Anti-non-Gal antibody levels varied considerably among individual sera and comprised approximately 10% of total anti-porcine antibodies without sex or age differences. Among the IgG subclasses only IgG1 and IgG2 were detected. Human serum-induced E-selectin expression on Gal-/- cells was less than 20% compared with Gal+/+ cells, correlated with anti-HD IgM and IgG antibody levels (P=0.027 and 0.032, respectively), and was largely complement-independent in accordance with the lack of IgG3 anti-non-Gal antibodies. In contrast, E-selectin upregulation on Gal+/+ cells was reduced in complement blocking experiments. CONCLUSION: Preformed anti-non-Gal antibodies, in particular anti-HD antibodies, were present in all human sera samples, activated porcine endothelial cells, and may therefore play a role in xenograft rejection using organs from GalT-/- pigs.     

Human complement-activating immunoglobulin (Ig)G3 antibodies are essential for porcine endothelial cell activation

BACKGROUND: Complement-activating naturally occurring anti-porcine endothelial cell antibodies (Abs) are responsible for hyperacute rejection in porcine-to-primate transplantation, whereas the role of complement in acute vascular rejection, characterized by type II endothelial cell activation, is less well understood. We previously demonstrated a correlation between porcine type II endothelial cell activation, as detected by E-selectin expression, and human immunoglobulin (Ig)G3 anti-Gal alpha1-3Gal (Gal) Abs, which was not seen for IgG1, IgG2 or IgG4. The present study was undertaken to investigate whether there is a causal relationship between human anti-porcine IgG3 Abs and porcine endothelial cell activation. METHODS: IgG3 was isolated employing a Protein A column to 98.3% purity. Porcine endothelial cells were incubated with isolated human IgG3 or the combination of IgG1, IgG2 and IgG4. E-selectin expression and complement activation were investigated by flow cytometry and Western blotting, respectively. RESULTS: Purified IgG3, in contrast to the other IgG subclasses, induced a substantial increase in E-selectin expression. This activation was accompanied by complement activation as detected by C3 cleavage, and was abolished by heat inactivation or by adding the complement inhibitor FUT-175. Depletion of anti-Gal Abs reduced E-selectin expression by 60%, consistent with the presence of complement-activating anti-porcine non-Gal Abs of the IgG3 subclass. CONCLUSIONS: Collectively, these data strengthen the hypothesis that human anti-porcine endothelial cell Abs of the IgG3 subclass are essential for endothelial cell activation in porcine-to-human species grafts and demonstrate such activation to be partly independent of Gal epitopes.     

Synergistic Deposition of C4d by Complement-Activating and Non-activating Antibodies in Cardiac Transplants

The role of non-complement-activating alloantibodies in humoral graft rejection is unclear. We hypothesized that the non-complement-activating alloantibodies synergistically activate complement in combination with complement-activating antibodies. B10.A hearts were transplanted into immunoglobulin knock out (Ig-KO) mice reconstituted with monoclonal antibodies to MHC class I antigens. In allografts of unreconstituted Ig-KO recipients, no C4d was detected. Similarly, reconstitution with IgG1 or low dose IgG2b alloantibodies did not induce C4d deposition. However, mice administered with a low dose of IgG2b combined with IgG1 had heavy linear deposits of C4d on vascular endothelium. C4d deposits correlated with decreased graft survival. To replicate this synergy in vitro, mononuclear cells from B10.A mice were incubated with antibodies to MHC class I antigens followed by incubation in normal mouse serum. Flow cytometry revealed that both IgG2a and IgG2b synergized with IgG1 to deposit C4d. This synergy was significantly decreased in mouse serum deficient in mannose binding lectin (MBL) and in serum deficient in C1q. Reconstitution of MBL-A/C knock out (MBL-KO) serum with C1q-knock out (C1q-KO) serum reestablished the synergistic activity. This suggests a novel role for non-complement-activating alloantibodies and MBL in humoral rejection.     

Antigen restriction and IgG subclasses among anti-GBM autoantibodies

Thirty-seven sera positive for anti-GBM antibodies (antibodies against the 'Goodpasture antigen' = NC1-domain of collagen IV) in routine analysis were studied for antigen restriction and IgG subclasses. Four different polypeptides, the four alpha-chains (alpha 1, alpha 2, alpha 3 and alpha 4) of human collagen IV NC1, were used as coating in ELISA assays. Autoantibodies were detected with monoclonal antibodies towards human IgG subclasses. All patients had antibodies to the alpha 3 chain, and most patients reacted much more to the alpha 3 peptide than to any of the other three peptides. This shows that the NC1 domain of the alpha 3 chain of collagen IV is the major target for anti-GBM antibodies. A minor group of patients, 6 of 37, showed no antigen restriction and had only moderate titres. It remains to be studied, however, whether they have antibodies to another epitope and a different clinical picture. All four subclasses of IgG antibodies were present, but IgG1 antibodies dominated. A group, consisting of females mainly, had relatively high titres of IgG4 antibodies to the NC1 domain of the alpha 3 chain of collagen IV.     

IgG subclass distribution of autoantibodies to glomerular basement membrane in Goodpasture's syndrome compared to other autoantibodies

The IgG subclass distribution of autoantibodies to glomerular basement membrane (anti-GBM antibodies) was investigated and compared to the distribution of liver-kidney microsomal (LKM) autoantibodies in chronic active hepatitis, to antimitochondrial autoantibodies (AMA) in primary biliary cirrhosis, and to the subclass distribution of total serum IgG within a healthy population. Solid phase assays for the demonstration of these autoantibodies were performed with four mouse monoclonal antibodies specific for each human subclass to provide quantitative data for the autoantibodies. In addition, the subclass distribution of total IgG in these sera was analyzed. IgG1 accounted for 75% of the total antibody activity in anti-GBM antibodies. In LKM antibodies a more homogeneous distribution was observed between the different subclasses with a relative high proportion of IgG4 autoantibodies (21.2%). In AMA a high proportion of IgG3 subclass autoantibodies was found (anti-p-48 = 28.7%, anti-p-62 = 29.9%). In these patients a high proportion of IgG3 (23 vs. 27.2%) could also be demonstrated in the subclass distribution of total IgG, whereas in patients with anti-GBM antibodies and LKM antibodies the subclass distribution of total IgG was comparable to a population of healthy volunteers. We conclude that the subclass distribution in anti-GBM antibodies differs from the distribution in other autoimmune diseases and from a healthy population and that these differences may be of pathogenetic relevance.     

Anti-CD20 antibody suppresses anti-HLA antibody formation in a HLA-A2 transgenic mouse model of sensitization

BACKGROUND: B cell depletion by anti-CD20 antibody is used in desensitization protocols and for treatment of antibody-mediated rejection (AMR). However, little is known about the efficacy and the mechanism(s) of action. METHODS: A mouse model of HLA sensitization was used to study the effectiveness of anti-CD20 treatment on B cell depletion and anti-HLA antibody suppression. RESULTS: Immunization of C57BL/6 mice with skin grafts from a transgenic C57BL.Tg/HLA-A2.1 mouse resulted in robust production of anti-HLA IgM and IgG antibodies, and accelerated rejection of a secondary skin allograft (within 3 days) featured by intragraft IgG and C4d deposition. Both IgM and IgG alloantibodies are specific to HLA-A2 as well as to a panel of class I HLA, including A1, A3, A25, A26, A29, and A30. These alloantibodies were complement-dependently cytotoxic (CDC) against HLA-A2 expressing target cells. Administration of 2 doses of a mouse-anti-mouse CD20 monoclonal antibody significantly reduced the levels of anti-HLA IgG2a antibodies, suppressed serum CDC, and prolonged survival of the secondary skin allografts. Suppression of anti-HLA IgG antibodies was associated with significant depletion of B220(+)/CD5(-) B cells from the blood, the spleen and the bone marrow of the treated animals. CONCLUSION: Anti-CD20 treatment effectively depletes B220(+)/CD5(-) B cells, resulting in potent suppression of anti-HLA IgG and prolongation of skin graft survival. The data are in support for the use of anti-CD20 antibodies in highly-HLA sensitized patients undergoing desensitization and for the treatment of AMR.     

Significance of IgG4 in the diagnosis of mucous membrane pemphigoid.

OBJECTIVE: To determine the diagnostic value and frequency of tissue deposition of IgG4 in comparison to polyclonal IgG, IgA, IgM, and C3. STUDY DESIGN: Oral mucosal biopsies of 82 patients clinically suspected to have mucous membrane pemphigoid (MMP) were analyzed by direct immunofluorescence (IF) using polyclonal anti-human IgG, IgM, IgA, fibrin, complement C3, and anti-human IgG4 subclass monoclonal antibodies. RESULTS: Based on clinical, hematoxylin and eosin (H & E), and direct IF studies, 34 cases were diagnosed as MMP. The most common antibody deposited was IgG (90%), followed by C3 (82%), and IgG4 (71%). In more than half the cases of MMP, IgG4 deposition was seen in combination with IgG and or C3. Strikingly, IgG4 was the sole antibody detected in 2 cases (6%). CONCLUSION: Our results suggest that the use of monoclonal IgG4 is important in the diagnosis of MMP. We suggest adding monoclonal IgG4 to the routine panel of antibodies used in studies of cases suspected to have MMP to avoid false-negatives.     

Skewing of pretransplant anti-HLA class I antibodies of immunoglobulin G isotype solely toward immunoglobulin G1 subclass is associated with poorer renal allograft survival

Sensitized patients with lymphocytotoxic immunoglobulin (Ig)G anti-human leukocyte antigen (HLA) antibodies have an increased risk of rejection and poorer graft survival. Little is known, however, about the correlation between IgG antibody subclass and clinical outcomes. We identified 20 sensitized renal transplant recipients (panel reactive antibody >15%), all of whom had anti-HLA class I antibodies of an IgG isotype with known specificity before transplantation but who received a crossmatch negative graft. We analyzed the degree of skewing solely toward IgG1 (n=11) or to other IgG subclasses with or without IgG1 (n=9) and correlated these findings with graft survival. At last follow-up (median follow-up 28 months), 6 of 11 patients (55%) with anti-HLA antibodies skewed toward IgG1 had lost their grafts compared with 0 of 9 patients (0%) with anti-HLA antibodies not skewed toward IgG1 (P =0.01 log-rank test). Anti-HLA antibodies of an IgG1 subclass may be a novel marker predicting poor graft outcome.     

Effect of IVIG administration on complement activation and HLA antibody levels

The objective of the present study was to determine if there are changes on complement (C) activation and concentration of HLA antibodies (Abs) in patients treated with intravenous immunoglobulin (IVIG). The patients evaluated were given IVIG as treatment of Ab‐mediated rejection or desensitization. The patients’ sera obtained before and after IVIG administration were tested for their effects on the deposition of both IgG (HLA Abs) and C3b (C activation) as measured by flow cytometry on T cells. IVIG consistently inhibited C activation when measured shortly after IVIG infusion but returned to the initial levels at 2–4 weeks, when total serum IgG also returned to pre‐infusion levels. C inhibition was more pronounced with higher IVIG doses and the degree of inhibition was inversely proportional to the HLA Ab concentrations. IVIG did not block the binding of HLA Abs immediately after administration, although levels were slightly but consistently lower after several monthly IVIG infusions. The data show that C inhibition by IVIG is short‐lived and that IVIG induces only a mild reduction of HLA Abs, seen not immediately but after months of treatment. These results may explain the inconsistent results of IVIG to achieve desensitization.     

Specific IgG subclass antibody pattern to Aspergillus fumigatus in patients with cystic fibrosis with allergic bronchopulmonary aspergillosis (ABPA).

BACKGROUND: IgG and IgG subclass antibodies to Aspergillus fumigatus (A fumigatus) were measured in a large population of patients with cystic fibrosis to elucidate a putative antibody pattern specific for allergic bronchopulmonary aspergillosis (ABPA). METHODS: An ELISA technique using water soluble somatic hyphal (WSSH) A fumigatus antigens and subclass specific monoclonal antibodies was used for cross sectional quantification of IgG and IgG1-4 subclass antibody levels in the serum of 238 patients with cystic fibrosis and 107 healthy controls. RESULTS: In patients with cystic fibrosis persistently colonised with A fumigatus the subclass antibody levels were significantly increased compared with patients with cystic fibrosis never or rarely colonised (p < 0.001). The group of patients persistently colonised with A fumigatus with ABPA (+Af+ABPA) had significantly increased levels of IgG antibodies to A fumigatus (Af-IgG) (median 69 ELISA units (EU) versus 31) and of subclasses Af-IgG1 (91 versus 27), Af-IgG2 (143 versus 56), and Af-IgG4 antibodies (72 versus 20), but not of IgG3 (17 versus 15), compared with the colonised patients without ABPA (+Af-ABPA). Patients with cystic fibrosis with no or only rare isolates of A fumigatus without ABPA (-Af-ABPA) also had significantly increased subclass antibody levels (Af-IgG1 9 versus 3, Af-IgG2 28 versus 5, Af-IgG4 16 versus 4; p < 0.001) compared with healthy controls. Low, although detectable, levels of antibodies were demonstrated in healthy controls. ABPA seemed to occur independently of Pseudomonas aeruginosa infection. Using diagnostic cut off levels for ABPA, sensitivity and specificity were calculated. The highest specificity was found for IgG4 (88%); sensitivity was between 65% and 73%. The positive predictive values (PPV) were moderate, whereas the negative predictive values (NPV) were high (96% in all subclasses except IgG3 with 94%). PPV increased to 50% if IgG1 as well as IgG2 and IgG4 were included. CONCLUSIONS: In a large number of unselected patients with cystic fibrosis significantly increased levels of Af-specific antibodies belonging to total IgG and all four subclasses were found in all groups of patients compared with healthy controls. In patients persistently colonised with A fumigatus these levels were significantly higher than in non-colonised patients, and the significantly highest levels (with the exception of IgG3) were found in patients with ABPA. Using a sensitive ELISA technique, measurements of IgG and IgG subclass antibodies to A fumigatus might be of importance in the management of ABPA, especially as a screening test to exclude the presence of ABPA; other tests are needed to confirm the diagnosis.     

Human leukocyte antigen class I epitopes: update to 103 total epitopes, including the C locus

BACKGROUND: Epitopes of human leukocyte antigen (HLA) are the sites to which the antibodies bind. We identify here 103 HLA class I epitopes shared by groups of class I antigens. In particular, our emphasis was on identifying epitopes exclusive to the C-locus antigens or interlocus epitopes among A, B, and C antigens. The use of monoclonal antibodies or alloantibodies eluted from HLA recombinant single antigen cell lines tested with a panel of single antigen beads have proved very useful in the identification of the epitopes. METHODS: Alloantibodies absorbed onto then eluted from HLA single antigen cell lines and monoclonal antibodies were tested with a panel of 95 A-, B-, and C- single antigen beads and the HLA specificities determined. Each epitope was defined by amino acids shared exclusively by the positive antigens for each antibody. RESULTS: In addition to the 58 A and B class I epitopes identified in an earlier study, we add 45 more new A, B, C epitopes including, for the first time, epitopes found on C locus antigens. CONCLUSION: Beads bearing single antigens tested with monoclonal or eluted alloantibodies proved very powerful in identifying epitopes shared among HLA antigens. These epitopes are the targets of the antibodies. Antibody specificities to non-donor-specific antigens, often found in sera of transplant patients, can now be understood as reactions to epitopes shared with the donor specific antigens. The importance of identifying these epitopes is that they may be the "transplantation antigens" responsible for antibody-mediated transplant rejection.     

Human NK cell and ADCC reactivity against xenogeneic porcine target cells including fetal porcine islet cells

ABSTRACT: In vitro studies of human NK cell-mediated cytotoxicity and ADCC against porcine target cells were performed. Stimulation of human PBMC responder cells with either allogeneic or xenogeneic porcine cells led to a marked increase in NK cell reactivity. Maximum reactivity was reached following 3–6 days of in vitro culture. The sensitivity of target cells ranked as follows: K562 > porcine PHA-induced lymphoblasts > resting porcine PBMC. Limiting dilution analysis showed that allo- and xeno-stimulation in vitro led to differentiation of similar frequencies of effector NK cells. Split culture experiments showed that single NK effector cells were cytotoxic against both K562 and porcine lymphoblasts, demonstrating that individual NK cells lack species specificity. NK effector cell generation stimulated by xenogeneic cells was cyclosporin A (CsA) sensitive and dependent on the presence of autologous responder T lymphocytes, a dependence that was completely reconstituted by the sole addition of human IL-2. Xenostimulation of enriched CD3+ cells also led to a preferential appearance of CD 16+ or CD56+ lymphoblasts.
Natural xenoreactive human anti-porcine antibodies are mainly of IgM and IgG2 subclasses, but antibodies in xenoimmunised patients reactive against porcine lymphocytes and fetal porcine islet cells were also of IgG1 and IgG3 subclasses. The same subclass distribution was found among antibodies specific for galα1,3 gal epitopes as shown by tests performed with α1,3 galactosyltransferase-transfected Raji cells (human Burkitt lymphoma cells). Natural antibodies did not mediate ADCC, whereas galα1,3 gal-specific antibodies in sera from xenoimmunised patients did. Fetal porcine islet cells were sensitive to human NK cell-mediated cytotoxicity and to ADCC mediated by xenoimmune sera.