Impact of cytomegalovirus infection on B cell differentiation and cytokine production in multiple sclerosis

Background

Human cytomegalovirus (HCMV) infection has been recently associated with a low risk of multiple sclerosis (MS), yet the basis behind this observation remains uncertain. In this study, we aimed to determine in MS patients whether HCMV induces modifications in the peripheral B cell compartment.

Methods

HCMV serostatus was determined in 73 MS patients (55 relapsing-remitting MS (RRMS); 18 progressive MS (PMS)) and 30 healthy controls, assessing their B cell immunophenotype and cytokine production (GM-CSF, IL-6, IL-10, and TNFα) by flow cytometry.

Results

HCMV seropositivity in untreated MS patients (n = 45) was associated with reduced switched memory B cells, contrasting with an opposite effect in PMS. Expansions of transitional B cells were observed in HCMV(+) IFNβ-treated RRMS patients but not in HCMV(−) cases (p < 0.01), suggesting that HCMV may influence the distribution of B cell subsets modulating the effects of IFNβ. Considering the B cell functional profile, HCMV(−) PMS displayed an increased secretion of proinflammatory cytokines (IL-6, TNFα) as compared to HCMV(+) PMS and RRMS cases (p < 0.001).

Conclusions

Our study reveals an influence of HCMV infection on the phenotype and function of B cells, promoting early differentiation stages in RRMS and reducing the proinflammatory cytokine profile in advanced MS forms, which might be related with the putative protective role of this virus in MS.

Impact of persistent and cleared preformed HLA DSA on kidney transplant outcomes

Preformed HLA donor-specific antibodies (DSA) only detected with Luminex have been associated with increased risk of antibody-mediated rejection (ABMR) and graft failure after kidney transplantation (KT). Their evolution after KT may modify this risk. We analyzed postransplant evolution of preformed DSA identified retrospectively and their impact on outcomes of 370 KT performed 2006-2014. Antibodies were monitored prospectively at 1-3-5 years after KT and if any dysfunction. Early acute ABMR was more frequent among patients with preformed DSA class-I or I + II than isolated class-II (29.4% vs 4.5%, p = 0.02). One year post-KT, 20 of 34 patients with functioning KT had persistent DSA. Preformed DSA class-II persisted more frequently than class-I/I + II (66.7% vs 33.3%; p = 0.031). The only risk factor independently associated with persistence was pretransplant MFI. Patients with de novo DSA had the highest risk of ABMR (HR 22.2 [CI 6.1-81.2]). Although recipients with persisting preformed DSA had significantly increased ABMR risk (HR 14.7 [CI 6.5-33.0]), those with cleared preformed DSA also had a higher risk than those without DSA (HR 7.01 [CI 2.2-21.8]). Preformed DSA are a very important risk factor for ABMR and graft loss. Patients who clear preformed DSA still show an increased risk of ABMR and graft loss after KT.

Increased levels of citrullinated antithrombin in plasma of patients with rheumatoid arthritis and colorectal adenocarcinoma determined by a newly developed ELISA using a specific monoclonal antibody

Citrullination is a post-translational modification that plays essential roles in both physiological processes and disease. Recent studies have found increased levels of citrullinated antithrombin in patients with rheumatoid arthritis and in different malignant tumours. Antithrombin, the main haemostatic serpin, loses its anticoagulant function via citrullination, which might contribute to the pathogenesis or thrombotic side effects of these disorders. We have developed a specific monoclonal antibody against citrullinated antithrombin. We determined the levels of citrullinated antithrombin and anti-FXa activity in plasma from 66 donors, 17 patients with rheumatoid arthritis and 77 patients with colorectal adenocarcinoma (42 suffering from venous thrombosis). Healthy subjects had negligible amounts of citrullinated antithrombin in plasma (7.9 ± 22.1 ng/ml), while it significantly increased in patients with rheumatoid arthritis or adenocarcinoma (159.7 ± 237.6 ng/ml and 36.8 ± 66.1 ng/ml), levels that, however, did not modify the plasma anticoagulant activity. Moreover, we did not find association between citrullinated antithrombin and the thrombotic risk in patients with adenocarcinoma. In conclusion, we have developed an antibody specific for citrullinated antithrombin that allows its quantification in biological samples, offering a new tool for the analysis of citrullination in different diseases. We confirm increased levels of citrullinated antithrombin in plasma of patients with rheumatoid arthritis and adenocarcinoma. This modification, probably local, could have pathological consequences in both disorders, but only affects a minor fraction of plasma antithrombin, resulting in no significant reduction of global anticoagulant activity. This result explains the absence of association of this marker with an increased risk of thrombosis in patients with colorectal adenocarcinoma.

PARP-2 sustains erythropoiesis in mice by limiting replicative stress in erythroid progenitors

Erythropoiesis is a tightly regulated process in which multipotential hematopoietic stem cells produce mature red blood cells. Here we show that deletion of poly(ADP-ribose) polymerase-2 (PARP-2) in mice leads to chronic anemia at steady state, despite increased erythropoietin plasma levels, a phenomenon not observed in mice lacking PARP-1. Loss of PARP-2 causes shortened lifespan of erythrocytes and impaired differentiation of erythroid progenitors. In erythroblasts, PARP-2 deficiency triggers replicative stress, as indicated by the presence of micronuclei, the accumulation of γ-H2AX (phospho-histone H2AX) in S-phase cells and constitutive CHK1 and replication protein A phosphorylation. Transcriptome analyses revealed the activation of the p53-dependent DNA-damage response pathways in PARP-2-deficient cells, culminating in the upregulation of cell-cycle and cell death regulators, concomitant with G2/M arrest and apoptosis. Strikingly, while loss of the proapoptotic p53 target gene Puma restored hematocrit levels in the PARP-2-deficient mice, loss of the cell-cycle regulator and CDK inhibitor p21 leads to perinatal death by exacerbating impaired fetal liver erythropoiesis in PARP-2-deficient embryos. Although the anemia displayed by PARP-2-deficient mice is compatible with life, mice die rapidly when exposed to stress-induced enhanced hemolysis. Our results pinpoint an essential role for PARP-2 in erythropoiesis by limiting replicative stress that becomes essential in the absence of p21 and in the context of enhanced hemolysis, highlighting the potential effect that might arise from the design and use of PARP inhibitors that specifically inactivate PARP proteins.

Parp-1 genetic ablation in Ela-myc mice unveils novel roles for Parp-1 in pancreatic cancer

Pancreatic cancer has a dismal prognosis and is currently the fourth leading cause of cancer-related death in developed countries. The inhibition of poly(ADP-ribose) polymerase-1 (Parp-1), the major protein responsible for poly(ADP-ribosy)lation in response to DNA damage, has emerged as a promising treatment for several tumour types. Here we aimed to elucidate the involvement of Parp-1 in pancreatic tumour progression. We assessed Parp-1 protein expression in normal, preneoplastic and pancreatic tumour samples from humans and from K-Ras- and c-myc-driven mouse models of pancreatic cancer. Parp-1 was highly expressed in acinar cells in normal and cancer tissues. In contrast, ductal cells expressed very low or undetectable levels of this protein, both in a normal and in a tumour context. The Parp-1 expression pattern was similar in human and mouse samples, thereby validating the use of animal models for further studies. To determine the in vivo effects of Parp-1 depletion on pancreatic cancer progression, Ela-myc-driven pancreatic tumour development was analysed in a Parp-1 knock-out background. Loss of Parp-1 resulted in increased tumour necrosis and decreased proliferation, apoptosis and angiogenesis. Interestingly, Ela-myc:Parp-1(-/-) mice displayed fewer ductal tumours than their Ela-myc:Parp-1(+/+) counterparts, suggesting that Parp-1 participates in promoting acinar-to-ductal metaplasia, a key event in pancreatic cancer initiation. Moreover, impaired macrophage recruitment can be responsible for the ADM blockade found in the Ela-myc:Parp-1(-/-) mice. Finally, molecular analysis revealed that Parp-1 modulates ADM downstream of the Stat3-MMP7 axis and is also involved in transcriptional up-regulation of the MDM2, VEGFR1 and MMP28 cancer-related genes. In conclusion, the expression pattern of Parp-1 in normal and cancer tissue and the in vivo functional effects of Parp-1 depletion point to a novel role for this protein in pancreatic carcinogenesis and shed light into the clinical use of Parp-1 inhibitors.

Therapeutic treatment with poly(ADP-ribose) polymerase inhibitors attenuates the severity of acute pancreatitis and associated liver and lung injury

BACKGROUND AND PURPOSE

The mortality associated with acute pancreatitis (AP) is largely attributable to abnormalities that occur in distant organs and supportive care remains the only treatment for patients with these complications. Recently, prophylactic pharmacological blockade of poly(ADP-ribose) polymerase (PARP) enzymes has been shown to attenuate the severity of the disease. However, the clinical relevance of PARP inhibitors administered after the onset of AP remains uncertain. The aim of the present study was to investigate the therapeutic effects of PARP inhibitors in established AP.

EXPERIMENTAL APPROACH

Mice were fed a choline/methionine-deficient/ethionine-supplemented (CMDE) diet to induce AP. PARP inhibitors were given at 36 h after the onset of CMDE diet. Severity of pancreatitis was assessed by measurements of serum amylase, lipase, IL-1beta and IL-6, and histological grading. Serum hepatic enzymes, myeloperoxidase (MPO) activity and morphological changes were measured as indicators of hepatic insult. Lung injury was evaluated by MPO activity and morphological changes. Survival rates of mice were monitored for 7 days.

KEY RESULTS

CMDE diet administration resulted in a significant increase in serum amylase, lipase, IL-1beta, IL-6, alanine aminotransferase and aspartate aminotranferase levels, indicating AP and associated liver injury. Analysis of the histopathological changes in pancreas, liver and lung revealed extensive tissue damage. Treatment of mice with PARP-inhibitors after the onset of AP was associated with a reduction in the severity of AP and, accordingly, with a reduced mortality rate.

CONCLUSIONS AND IMPLICATIONS

Our results support the therapeutic application of PARP inhibitors in the treatment of established AP.

In vivo effects of hyperthermia on the functional and conformational characteristics of antithrombin

BACKGROUND

High temperatures produce in vitro transitions of antithrombin to its inactive latent and polymeric forms. Accordingly, high body temperatures might contribute in vivo to conformational changes in antithrombin associated with increased thrombotic risk.

METHODS

We assessed the in vivo effects of different hyperthermic stimuli on antithrombin. We studied two mouse models of hyperthermia. (i) Febrile syndrome induced by turpentine. (ii) Heat stroke generated by exposure to 42 degrees C. Body temperatures were measured. Antigen, anti-factor Xa activity and conformational features of plasma antithrombin were studied. Furthermore, structural and ultrastructural features from livers were analyzed. Intracellular retention of serpins (antithrombin and alpha1-antitrypsin) was studied by western-blotting, immunohistochemistry, and immunogold-labeling-electron microscopy.

RESULTS

Hyperthermic stimuli caused a moderate deficiency of circulating antithrombin and a slight increase in its latent form. Moreover, hyperthermia caused intracellular retention of antithrombin into aggregates within the lumen of the endoplasmic reticulum of hepatocytes. This effect was similar for alpha1-antitrypsin.

CONCLUSION

Hyperthermia causes minor conformational changes on circulating antithrombin in vivo, although it has severe consequences for intracellular antithrombin and other hepatic serpins, inducing the intracellular retention of the nascent protein. These effects may contribute to the moderate plasma deficiency of antithrombin and the increased thrombotic risk detected in hyperthermic conditions.

Prevention of hyperacute rejection in a model of orthotopic liver xenotransplantation from pig to baboon using polytransgenic pig livers (CD55, CD59, and H-transferase)

INTRODUCTION

The search for alternative sources for transplant organs leads us to the search for animals as an inexhaustible source of organs. The objective of this study was to analyze whether livers from polytransgenic pigs expressing the human complement regulatory proteins CD55 (hDAF), CD59, and alfa alpha1,2-fucosyltransferase (H-transferase), protected against hyperacute rejection after orthotopic liver xenotransplantation to a baboon and also to study pig liver function in a nonhuman primate.

MATERIALS AND METHODS

Nine liver transplants from pig to baboon were divided into two groups: a control group (n = 4) of genetically unmodified pigs and an experimental group (n = 5) of pigs transgenic for CD55, CD59, and H-transferase as donors. All the donating piglets obtained through hysterectomy were maintained in specific pathogen-free conditions. The selection of transgenic pig donors followed demonstration of transgene expression using monoclonal antibodies (antiCD55, antiCD59) and immunohistological studies on liver biopsies.

RESULTS

All animals in the control group developed hyperacute rejection with survival rates less than 16 hours without function of transplanted livers. In the experimental group none of the animals suffered hyperacute rejection. Survival in this group was between 13 and 24 hours. The livers were functional, producing bile and maintaining above 35% prothrombin activity. Only in one case was there primary dysfunction of the xenograft.

CONCLUSION

Polytransgenic livers for complement regulatory proteins prevent hyperacute rejection when xenotransplanted into a baboon.

Biochemical characterization of recombinant and circulating human Spalpha

Human Spalpha is a soluble protein expressed by macrophages present in lymphoid tissues (spleen, lymph node, thymus, and bone marrow), for which little functional and structural information is available. It belongs to the group B of the scavenger receptor cysteine-rich superfamily (SRCR-SF) that includes the lymphocyte surface receptors CD5 and CD6 among others. Spalpha is able to bind to different cells of the immune system (monocytes and lymphocytes), which suggests that it may play an important role in the regulation of this system. To study Spalpha, an episomal mammalian expression system (pCEP-Pu/HEK 293-EBNA) was used to produce a recombinant form (rSpalpha) that was utilized for biochemical studies and for the generation of specific hybridomas. Four monoclonal antibodies were selected for their reactivity against rSpalpha by Western blot, immunoprecipitation, and enzyme-linked immunosorbent assays. The monoclonal antibodies recognized three different epitopes on Spalpha. The monoclonal antibodies revealed the existence of two Spalpha isoforms of 38 and 40 kDa, resulting from different sialic acid content. They also showed that Spalpha is a relatively abundant serum protein (60 micro g/ml) that mostly circulates in association with other serum proteins. Accordingly, rSpalpha allowed affinity chromatography isolation of polyclonal and monoclonal immunoglobulin M (IgM). These data indicate that Spalpha is a circulating protein that may play a role in the homeostasis of IgM antibodies.

Human anti-porcine gammadelta T-cell xenoreactivity is inhibited by human FasL expression on porcine endothelial cells

BACKGROUND

The role of gammadelta T cells during an immune response is still elusive and has been proposed to play a first line of defense along with other cells of the innate immune system, such as macrophages and natural killer cells, before alphabeta T-cell activation occurs. Innate cellular immune response plays a major role in xenograft rejection. We investigated the response of human gammadelta T cells to unmodified and human FasL (hFasL)-expressing xenogenic porcine endothelial cells.

METHODS

A 51Cr release assay was used to study the xenoreactivity of human gammadelta T-cell clones against porcine endothelial cells. Stable transfectants of porcine endothelial cells expressing hFasL were established and analyzed for their effectiveness in controlling this response.

RESULTS

Of the gammadelta T-cell clones tested, 38.9% were cytotoxic for porcine endothelial target cells. This cytotoxic response of human gammadelta T-cell clones was significantly inhibited by a monoclonal antibody against human CD3. Incubation of gammadelta T-cell clones with concanamycin A, an inhibitor of the perforin/granzyme B pathway, caused inhibition of lysis of porcine endothelial cells. Inhibition was not observed upon incubation with either anti-FasL or anti-tumor necrosis factor-alpha monoclonal antibodies. Expression of hFasL on porcine endothelial cells significantly reduced lysis by human gammadelta T cells.

CONCLUSION

These results imply that human gammadelta T cells may represent an important obstacle to xenotransplantation. Specific strategies targeted at this subset of T cells could be important in controlling innate cellular response to xenografts and facilitate graft survival.

Genomic instability in a PARP-1(-/-) cell line expressing PARP-1 DNA-binding domain

Poly(ADP-ribose) polymerase-1 (PARP-1) is a nuclear DNA binding protein that participates in processes involving nicking and resealing DNA strands. A genomically unstable subpopulation of PARP-1(-/-) cells has recently been described, which disappears after stable transfection of the cells with complete PARP-1 cDNA. Here we investigate the role played by PARP-1 in the maintenance of genomic stability, independently of its enzymatic activity. We used a PARP-1-deficient cell line to express a DNA construct encoding the PARP-1 DNA-binding domain (DBD) fragment and one encoding the mutant DBDbd-, defective in binding to DNA strand breaks. We found that, in the absence of DNA damage, expression of DBD or DBDbd- mutant induces increased genomic instability in the PARP-1(-/-) cells. These results suggest that the DBD fragment of PARP-1, apart from its classical role of nick detection and DNA binding, is likely to participate in molecular complexes with proteins involved in genomic integrity.

Inhibition of apoptosis of a PARP(-)/(-)cell line transfected with PARP DNA-binding domain mutants

We have investigated the possibility of the involvement of PARP in apoptosis, independently of its enzymatic activity. We thus transfected PARP(-)/(-)A11 cells with a DNA construct encoding the PARP DNA-binding domain (DBD) fragment or mutants DBDbd(-), defective in DNA binding to DNA strand breaks, and DBDcl(-), resistant to caspase-3 cleavage. We found that in the absence of PARP, while expression of DBD has only a marginal effect, expression of the mutants strongly inhibits the apoptosis induced by staurosporine, as measured by the binding of annexin V. Moreover, the mutants, but not DBD, inhibit the cleavage of DNA PKcs, suggesting inhibition of activation of caspase-3. In addition, the mutant transfectants are fractionally less susceptible to low doses of an alkylating agent than the DBD transfectant or the original A11 line. The results suggest that the DBD fragment of PARP, apart from its classical role of nick detection and DNA binding, participates in complexes involved in upstream events leading to activation of the caspase cascade.

Monitoring and interpreting the intrinsic features of somatic hypermutation

We have used both normal and transgenic mice to analyse the recruitment and targeting of somatic hypermutation to the immunoglobulin loci. We compare methods for analysing hypermutation and discuss how large databases of mutations can be assembled by PCR amplification of the rearranged V-gene flanks from the germinal centre B cells of normal mice as well as by transgene-specific amplification from transgenic B cells. Such studies confirm that hypermutation is preferentially targeted to the immunoglobulin V gene with the bcl6 gene, for example, escaping this intense mutational targeting in germinal centre B cells. We review our data concerning the nature of the hypermutation domain and the targeting of hotspots within that domain. We consider how enhancer-mediated recruitment of hypermutation to the immunoglobulin loci operates in a clonally maintained fashion and illustrate how both the degree of expression and demethylation of the transgene broadly correlate with its mutability.

The 5' hypermutation boundary of kappa chains is independent of local and neighbouring sequences and related to the distance from the initiation of transcription

The hypermutation of antibody genes targets 1-2 kb of DNA which includes the rearranged V(D)J gene segments. The precise nature, location and limits of the targeted region are of considerable interest in terms of the mechanism of hypermutation. We have analyzed the frequency and distribution of mutations in the 5' region of immunoglobulins using several modified kappa transgenes. We found that the position of the boundary, relative to the transcription initiation site, is not affected by the sequence of the V segment or by substituting the kappa chain promoter for a beta-globin promoter. Furthermore, the deletion of the leader intron (containing the hypermutation boundary) does not affect hypermutation per se, but shifts the boundary from the leader intron to the V region such that the distance between the boundary and the site of initiation of transcription remains constant. These results show that the position of the hypermutation boundary (about 185 bases downstream of the site of initiation of transcription) is not defined by the nucleotide sequence but rather by the distance to a fixed upstream position. Although mutations are also observed in the region upstream of the boundary, the frequency at which they occur is one order of magnitude lower relative to the frequency observed in the V segment. Nonetheless this upstream mutation rate remains more than two orders of magnitude higher than that of somatic genes. We discuss possible mechanisms explaining the nature and position of the boundary in the context of an error-prone DNA repair model.

Cells strongly expressing Ig(kappa) transgenes show clonal recruitment of hypermutation: a role for both MAR and the enhancers

The V regions of immunoglobulin kappa transgenes are targets for hypermutation in germinal centre B cells. We show by use of modified transgenes that the recruitment of hypermutation is substantially impaired by deletion of the nuclear matrix attachment region (MAR) which flanks the intron-enhancer (Ei). Decreased mutation is also obtained if Ei, the core region of the kappa3'-enhancer (E3') or the E3'-flank are removed individually. A broad correlation between expression and mutation is indicated not only by the fact that the deletions affecting mutation also give reduced transgene expression, but especially by the finding that, within a single mouse, transgene mutation was considerably reduced in germinal centre B cells that poorly expressed the transgene as compared with strongly expressing cells. We also observed that the diminished mutation in transgenes carrying regulatory element deletions was manifested by an increased proportion of B cells in which the transgene had not been targeted at all for mutation rather than in the extent of mutation accumulation once targeted. Since mutations appear to be incorporated stepwise, the results point to a connection between transcription initiation and the clonal recruitment of hypermutation, with hypermutation being more fastidious than transcription in requiring the presence of a full complement of regulatory elements.

Nonsense mutations inhibit RNA splicing in a cell-free system: recognition of mutant codon is independent of protein synthesis

Mutations resulting in premature termination codons reduce the corresponding mRNA levels. We describe a cell-free system in which depletion of the mutant immunoglobulin kappa mRNA pool correlates with inefficient splicing and not with RNA decay. Splicing deficiency does not depend on the sequence surrounding the in-frame nonsense codon and can be partially corrected by mutating the methionine initiation codon. Despite the apparent link between translation and low mutant mRNA levels, inefficient splicing is not dependent on protein synthesis. Abnormal splicing of mutant immunoglobulin RNA is observed with B-cell but not with HeLa or T-cell extracts. A nonsense mutant beta-globin RNA is normally spliced by B-cell extract. We propose that the phenomenon exhibits tissue and gene specificity.

Association of the shared epitope with radiological severity of rheumatoid arthritis

OBJECTIVE

To investigate the association between radiological severity of rheumatoid arthritis (RA) and the presence of the shared epitope.

METHODS

Ninety unrelated adult Spanish patients with RA with a disease duration of at least 3 years, selected according to the American College of Rheumatology criteria, were radiologically assessed (shoulders, elbows, wrists, hands, hips, knees, and feet) and classified as having severe or nonsevere RA. DNA oligotyping was used to determine DR specificities and to detect DR4 and DR1 alleles.

RESULTS

Forty-one patients (45.5%) had severe RA. Sixty-six patients (73.3%) carried the shared epitope and 18 (20%) had double expression of the shared epitope. Thirty-seven (90%) of the 41 patients with severe RA expressed the shared epitope. Logistic regression analysis showed that both single and double expression of the shared epitope were strongly related to the radiological severity of RA (odds ratio = 6.3 and 9.4, respectively).

CONCLUSION

Our results show that radiological severity of RA is highly associated to the shared epitope.

Targeting of non-Ig sequences in place of the V segment by somatic hypermutation

Affinity maturation of antibodies is characterized by localized hypermutation of the DNA around the V segment. Here we show, using mice containing single or multiple transgene constructs, that an immunoglobulin V kappa segment can be replaced by human beta-globin or prokaryotic neo or gpt genes without affecting the rate of hypermutation; the V gene itself is not necessary for recruiting hypermutation. The ability to target hypermutation to heterologous genes in vivo could find more general applications in biology.

Frequency of HLA-DPB1 alleles in a Spanish population: their contribution to rheumatoid arthritis susceptibility

HLA-DPB1 allele frequencies in 181 unrelated control individuals and 70 rheumatoid factor-positive RA patients from Seville (Spain) were determined using oligonucleotide typing methods. All frequencies shown concern the percentage of individuals positive for a certain allele. HLA-DPB1*0401 was the most common DPB1 allele in the healthy individuals, possessed by 65.7% of them. In addition to HLA-DPB1*0401, only the following alleles were found in normal subjects at frequencies greater than 10%: DPB1*0101 (15.5%), DPB1*0201 (12.2%), DPB1*0301 (16.6), and DPB1*0402 (29.3%). When HLA-DPB1 allelic frequencies were compared between seropositive RA patients and controls, a negative association for DPB1*0301 and DPB1*0401 was found in RA patients, although it failed to reach statistical significance after correction for the number of comparisons made. The other DPB1 alleles exhibited almost identical frequencies in both groups. However, when only DR4+ patients and controls were considered, the decrease in the frequency of the DPB1*0301 and DPB1*0401 alleles lacked statistical significance. On the other hand, when DR4- RA patients and controls were compared, the frequency of DPB1*0301 was found decreased significantly again, even more than in the whole group of patients.

Distribution of HLA-A*28 alleles in a Spanish population

DNA oligotyping was used to determine HLA-A28 subtypes in 25 unrelated Caucasian individuals living in or around Seville, Spain. Results showed that HLA-A*6802 was the most frequent allele, found in 14 individuals (53.8%), followed by HLA-68.3, which was present in eight subjects (30.8%), and both combined represented 84.6% of A28+ individuals in the area. The HLA-A*6801 allele was found in three individuals (11.5%), whereas HLA-A*6901 was present in one subject only (3.8%). Results indicate that the distribution of HLA-A28 alleles can vary among different Caucasoid populations. In this way, the high frequency obtained for A*6802 supports previous studies suggesting that the HLA-A*6802 allele was prevalent in people of the Mediterranean basin, in contrast to A*6801, prevalent in northern European populations.

Application of cellular ELISA (CELISA) to the detection of human monoclonal autoantibodies

This work describes the application of cellular enzyme-linked immunosorbent assay (CELISA) for the detection of both polyreactive and monospecific human monoclonal antibodies against autoantigens. The CELISA is ideally suited for the screening of a large number of hybridoma culture supernatants, being, in this way, superior to other methods commonly used for the detection of autoantibody activity, such as indirect immunofluorescence on tissue sections and slide cell preparations, in terms of speed and sensitivity. This assay demonstrated higher sensitivity than ELISA using autoantigenic extracts from rabbit thymus, human spleen, nucleoprotamine, and salmon sperm nuclei, and enzyme immunoassays using ssDNA, dsDNA, and affinity purified autoantigens as substrate. The CELISA has been also successfully applied to the detection of autolymphocytotoxic antibody activity in heterohybridoma supernatants.

A human monoclonal antibody reacting against HLA-DQ1-, DQ4-, and a subset of DQ7-bearing cells

Human mAb 2A2 recognizes an epitope present in the HLA-DQ1 + 4 specifications and also on several DQ7-positive cells. We have investigated the extra reactions of this monoclonal reagent on a wider panel of DQ1-, DQ4-negative/DQ7-positive B-cell lines. The results obtained support the existence of two subtypes of the HLA-DQ7 specificity on the basis of their reactivity with human mAb 2A2; the DQ7/2A2-positive variant has been found in 12 of 29 BCLs positive for the DR11 antigen, and in four of eight BCLs bearing DR4-DQ7 haplotypes. It has also been detected in the DR12-positive cells assayed and in several unusual DR/DQ7 combinations not commonly found in Caucasoid populations, including the DR13-DwHAG and DR14-Dw16 haplotypes. Results from competition binding assays between 2A2 and well-characterized murine anti-DQ polymorphic mAbs suggest that the epitope recognized by human mAb 2A2 on DQ1- or DQ4-bearing haplotypes is located on the DQ beta chains of such specificities, being amino acid residues 54-55, the potential binding site of antibody 2A2, whereas the binding site on DQ7 antigens cannot be explained on the basis of known amino acid sequences.

Application of the MAILA technique to the study of human anti-HLA monoclonal antibody specificity

The monoclonal antibody-specific immobilization of lymphocyte antigens (MAILA) assay was developed to detect antibodies present in human alloantisera against antigens of different major histocompatibility complex loci, particularly of class II specificity. The MAILA assay has been used in our laboratory to the determination of the type of HLA molecule recognized by human monoclonal antibodies 91C2 (anti-A2 + 28), 34F11 (anti-DQ1), and 2A2 (anti-DQ1 + 4 + short DQ7), using well characterized monomorphic as well as polymorphic murine monoclonals for the specific immobilization of HLA molecules. Results obtained show that the MAILA assay is also a valuable tool for the determination of specific human MHC locus products recognized by human monoclonal antibodies.