Complement-immunoglobulin interactions

A crucial role for Jagunal homolog 1 in humoral immunity and antibody glycosylation in mice and humans

Jagunal homolog 1 (JAGN1) has been identified as a critical regulator of neutrophil biology in mutant mice and rare-disease patients carrying JAGN1 mutations. Here, we report that Jagn1 deficiency results in alterations in the endoplasmic reticulum (ER) of antibody-producing cells as well as decreased antibody production and secretion. Consequently, mice lacking Jagn1 in B cells exhibit reduced serum immunoglobulin (Ig) levels at steady state and fail to mount an efficient humoral immune response upon immunization with specific antigens or when challenged with viral infections. We also demonstrate that Jagn1 deficiency in B cells results in aberrant IgG N-glycosylation leading to enhanced Fc receptor binding. Jagn1 deficiency in particular affects fucosylation of IgG subtypes in mice as well as rare-disease patients with loss-of-function mutations in JAGN1. Moreover, we show that ER stress affects antibody glycosylation. Our data uncover a novel and key role for JAGN1 and ER stress in antibody glycosylation and humoral immunity in mice and humans.

Long-term renal survival of γ3-heavy chain deposition disease: a case report

Background

Monoclonal immunoglobulin deposition disease (MIDD) is characterized by the non-amyloid deposition of monoclonal immunoglobulin fragments in the basement membranes. Heavy chain deposition disease (HCDD) is a type of MIDD. HCDD is an extremely rare disease, and only three cases have been reported in Japan up to the present. The prognosis of HCDD is very poor, and optimal treatment has not been established. Only a few cases of HCDD with favorable long-term renal prognosis have been reported to date.

Case presentation

The authors describe a 61-year-old woman who presented with massive proteinuria, progressive kidney impairment, and hypocomplementemia. Kidney biopsy was performed for a precise diagnosis. On light microscopy, glomerules were lobulated and presented with nodular sclerosing glomerulopathy with membranoproliferative glomerulonephritis-like features. Immunofluorescence studies were positive for IgG, C3, and C1q within the mesangial nodules and in a linear distribution along the capillary walls without associated deposition of light chains. Staining for IgG showed the presence of linear deposits along tubular basement membranes. The analysis of the IgG subclass stain demonstrated intense positivity for IgG3 only. Electron microscopy revealed non-organized electron-dense deposits in the expanded mesangial area and inner aspect of the glomerular basement membranes. In accordance with the histological findings, we diagnosed γ3-HCDD. There was no evidence of plasma cell dyscrasia as a result of bone marrow aspiration. Serum and urine monoclonal proteins were not detected by immunoelectrophoresis and immunofixation electrophoresis. The serum free light chain ratio was within normal range. At first, prednisolone was administrated at a dose of 40 mg/day. However, a therapeutic effect was not observed. Urinary protein was not decreased and renal function further deteriorated. Therefore, melphalan plus prednisolone (MP) therapy was initiated. After 4 courses of MP therapy, the clinical parameters, including proteinuria, serum creatinine, albumin, and complement level (C3 and C4) were ameliorated. To date, the patient has been followed for 28 months, and long-term renal survival has been observed.

Conclusions

In this case, hematologic disease such as multiple myeloma was not detected; however, MP therapy was effective. Recently, the novel concept of monoclonal gammopathy of renal significance (MGRS) has been reported. MIDD, which includes HCDD, is one category of MGRS. In MGRS, aggressive chemotherapy may induce favorable renal outcomes.

Dextrose-mediated aggregation of therapeutic monoclonal antibodies in human plasma: Implication of isoelectric precipitation of complement proteins

Many therapeutic monoclonal antibodies (mAbs) are clinically administered through intravenous infusion after mixing with a diluent, e.g., saline, 5% dextrose. Such a clinical setting increases the likelihood of interactions among mAb molecules, diluent, and plasma components, which may adversely affect product safety and efficacy. Avastin® (bevacizumab) and Herceptin® (trastuzumab), but not Remicade® (infliximab), were shown to undergo rapid aggregation upon dilution into 5% dextrose when mixed with human plasma in vitro; however, the biochemical pathways leading to the aggregation were not clearly defined. Here, we show that dextrose-mediated aggregation of Avastin or Herceptin in plasma involves isoelectric precipitation of complement proteins. Using mass spectrometry, we found that dextrose-induced insoluble aggregates were composed of mAb itself and multiple abundant plasma proteins, namely complement proteins C3, C4, factor H, fibronectin, and apolipoprotein. These plasma proteins, which are characterized by an isoelectronic point of 5.5–6.7, lost solubility at the resulting pH in the mixture with formulated Avastin (pH 6.2) and Herceptin (pH 6.0). Notably, switching formulation buffers for Avastin (pH 6.2) and Remicade (pH 7.2) reversed their aggregation profiles. Avastin formed little, if any, insoluble aggregates in dextrose-plasma upon raising the buffer pH to 7.2 or above. Furthermore, dextrose induced pH-dependent precipitation of plasma proteins, with massive insoluble aggregates being detected at pH 6.5–6.8. These data show that isoelectric precipitation of complement proteins is a prerequisite of dextrose-induced aggregation of mAb in human plasma. This finding highlights the importance of assessing the compatibility of a therapeutic mAb with diluent and human plasma during product development.

Genetic Association of the Porcine C9 Complement Component with Hemolytic Complement Activity

The complement system is a part of the natural immune regulation mechanism against invading pathogens. Complement activation from three different pathways (classical, lectin, and alternative) leads to the formation of C5-convertase, an enzyme for cleavage of C5 into C5a and C5b, followed by C6, C7, C8, and C9 in membrane attack complex. The C9 is the last complement component of the terminal lytic pathway, which plays an important role in lysis of the target cells depending on its self-polymerization to form transmembrane channels. To address the association of C9 with traits related to disease resistance, the complete porcine C9 cDNA was comparatively sequenced to detect single nucleotide polymorphisms (SNPs) in pigs of the breeds Hampshire (HS), Duroc (DU), Berlin miniature pig (BMP), German Landrace (LR), Pietrain (PIE), and Muong Khuong (Vietnamese potbelly pig). Genotyping was performed in 417 F2 animals of a resource population (DUMI: DU×BMP) that were vaccinated with Mycoplasma hyopneumoniae, Aujeszky diseases virus and porcine respiratory and reproductive syndrome virus at 6, 14 and 16 weeks of age, respectively. Two SNPs were detected within the third exon. One of them has an amino acid substitution. The European porcine breeds (LR and PIE) show higher allele frequency of these SNPs than Vietnamese porcine breed (MK). Association of the substitution SNP with hemolytic complement activity indicated statistically significant differences between genotypes in the classical pathway but not in the alternative pathway. The interactions between eight time points of measurement of complement activity before and after vaccinations and genotypes were significantly different. The difference in hemolytic complement activity in the both pathways depends on genotype, kind of vaccine, age and the interaction to the other complement components. These results promote the porcine C9 (pC9) as a candidate gene to improve general animal health in the future.

Recurrent proliferative glomerulonephritis with monoclonal IgG deposits of IgG2λ subtype in a transplanted kidney: a case report

Proliferative glomerulonephritis with monoclonal immunoglobulin G (IgG) deposits (PGNMID) is a recently described disease entity. In the kidney transplantation literature, only 6 recurrent and 2 de novo PGNMID cases, including 7 of the IgG3 subclass (6 with κ light chain and 1 with λ light chain) and 1 of the IgG1 subclass (λ light chain), have been described to date. We describe a 52-year-old man with end-stage renal disease whose primary glomerular disease had been suggested to be membranoproliferative glomerulonephritis. The patient underwent living related donor kidney transplantation and presented with proteinuria, hematuria, and decreased kidney function at 4 months posttransplantation. Biopsy of the transplanted kidney showed diffuse endocapillary proliferative glomerulonephritis. Immunofluorescence microscopy showed prominent granular glomerular staining for IgG, C3, and λ light chain, with IgM, IgA, and κ light chain undetectable. Immunofluorescence staining for IgG subclass showed signal for IgG2 only. Retrospective analysis of the native kidney biopsy specimen also showed the same monoclonal glomerular staining for the IgG2λ subtype. These findings led us to the diagnosis of PGNMID of the IgG2λ subtype as both the primary glomerular disease and recurrent disease in the transplanted kidney. Recurrence was treated with high-dose prednisolone, which decreased proteinuria, hematuria, and serum creatinine level. The case demonstrates that PGNMID of the IgG2λ subtype also can recur in the transplanted kidney.

IgM and its receptors: structural and functional aspects

This review combines the data obtained before the beginning of the 1990s with results published during the last two decades. The predominant form of the IgM molecule is a closed ring composed of five 7S subunits and a J chain. The new model of spatial structure of the pentamer postulates nonplanar mushroom-shaped form of the molecule with the plane formed by a radially-directed Fab regions and central protruding portion consisting of Cµ4 domains. Up to the year 2000 the only known Fc-receptor for IgM was pIgR. Interaction of IgM with pIgR results in secretory IgM formation, whose functions are poorly studied. The receptor designated as Fcα/µR is able to bind IgM and IgA. It is expressed on lymphocytes, follicular dendritic cells, and macrophages. A receptor binding IgM only named FcµR has also been described. It is expressed on T- and B-lymphocytes. The discovery of new Fc-receptors for IgM requires revision of notions that interactions between humoral reactions involving IgM and the cells of the immune system are mediated exclusively by complement receptors. In the whole organism, apart from IgM induced by immunization, natural antibodies (NA) are present and comprise in adults a considerable part of the circulating IgM. NA are polyreactive, germ-line-encoded, and emerge during embryogenesis without apparent antigenic stimuli. They demonstrate a broad spectrum of antibacterial activity and serve as first line of defense against microbial and viral infections. NA may be regarded as a transitional molecular form from invariable receptors of innate immunity to highly diverse receptors of adaptive immunity. By means of interaction with autoantigens, NA participate in maintenance of immunological tolerance and in clearance of dying cells. At the same time, NA may act as a pathogenic factor in atherosclerotic lesion formation and in development of tissue damage due to ischemia/reperfusion.

A case of γ1-heavy chain deposition disease successfully treated with melphalan and prednisolone therapy

Heavy chain deposition disease (HCDD) is characterized by glomerular and tubular deposition of non-amyloidotic monoclonal heavy chains without associated light chains. We describe a case of gamma1-HCDD who presented with nephrotic syndrome, microhematuria, and hypocomplementemia. Renal biopsy showed lobular and nodular glomerulosclerosis along with IgG and C3 deposition. Electron microscopy revealed electron-dense deposits on the glomerular and tubular basement membranes and mesangium. Congo red staining was negative. Staining was positive for IgG1 on glomerular and tubular basement membranes but negative for IgG2-4, kappa and lambda light chains. Staining for the constant heavy chain domains showed the deletion of the first constant heavy chain domain. Thus, we diagnosed gamma1-HCDD. She was considered to be early-stage HCDD because proteinuria and hematuria were not observed before the nephrotic syndrome onset. Melphalan and prednisolone (MP) therapy reduced proteinuria as well as improved renal function and complement levels. Although renal prognosis of HCDD is poor, aggressive chemotherapy with MP may be effective in early-stage HCDD patients.

Heavily isotype-dependent protective activities of human antibodies against vaccinia virus extracellular virion antigen B5

Antibodies against the extracellular virion (EV or EEV) form of vaccinia virus are an important component of protective immunity in animal models and likely contribute to the protection of immunized humans against poxviruses. Using fully human monoclonal antibodies (MAbs), we now have shown that the protective attributes of the human anti-B5 antibody response to the smallpox vaccine (vaccinia virus) are heavily dependent on effector functions. By switching Fc domains of a single MAb, we have definitively shown that neutralization in vitro--and protection in vivo in a mouse model--by the human anti-B5 immunoglobulin G MAbs is isotype dependent, thereby demonstrating that efficient protection by these antibodies is not simply dependent on binding an appropriate vaccinia virion antigen with high affinity but in fact requires antibody effector function. The complement components C3 and C1q, but not C5, were required for neutralization. We also have demonstrated that human MAbs against B5 can potently direct complement-dependent cytotoxicity of vaccinia virus-infected cells. Each of these results was then extended to the polyclonal human antibody response to the smallpox vaccine. A model is proposed to explain the mechanism of EV neutralization. Altogether these findings enhance our understanding of the central protective activities of smallpox vaccine-elicited antibodies in immunized humans.

Monoclonal immunoglobulin deposition disease associated with membranous features

BACKGROUND

Very few cases of non-organized and non-Randall-type monoclonal immunoglobulin deposition disease (MIDD) associated with membranous features have been reported. Information on clinicopathological features and prognosis in this entity is limited.

METHODS

We reviewed 5443 renal biopsies processed at our department, and identified three patients with MIDD associated with membranous features. We evaluated clinicopathological features and outcomes in these patients.

RESULTS

All patients had proteinuria, and one patient developed nephrotic syndrome. Renal insufficiency was not observed. Cryoglobulin or monoclonal protein in serum and urine was not detected. A renal biopsy showed thickening of the glomerular capillary walls and spike formation. Tubulointerstitial and vascular alterations were mild or absent. Immunofluorescence studies revealed granular IgG3-kappa deposits in two patients and IgG1-kappa deposits in one patient, along the glomerular capillary walls. Immunofluorescence studies using antibodies specific for gamma-heavy chain Fab containing C(H)1 domain, C(H)2 domain and C(H)3 domain did not show any apparent deletion. On confocal microscopy, glomerular colocalization of light and heavy chains was observed. Electron microscopy showed predominant subepithelial granular deposits without distinct ultrastructural organization. All patients were treated with steroids, and good effects were observed. A follow-up renal biopsy performed in one patient showed histological improvements. No patient developed myeloma or other haematological malignancy during the course of follow-up (mean 44 months).

CONCLUSIONS

MIDD associated with membranous features is an extremely rare but distinctive entity. Our study suggests glomerular deposition of a nondeleted whole immunoglobulin molecule. Patients with this entity appear to respond well to steroid therapy.

Immunology

The concept of forbidden foods that should not be eaten goes back to the Garden of Eden and apart from its religious meanings it may also have foreshadowed the concept of foods that can provoke adverse reactions. Thus we could say that allergic diseases have plagued mankind since the beginning of life on earth. The prophet Job was affected by a condition that following the rare symptoms described by the Holy Bible might be identified as a severe form of atopic dermatitis (AD). The earliest record of an apparently allergic reaction is 2621 B.C., when death from stinging insects was first described by hieroglyphics carved into the walls of the tomb of Pharaoh Menes depicting his death following the sting of a wasp. In 79 A.D., the death of the Roman admiral Pliny the Elder was ascribed to the SO₂-rich gases emanating from the eruption of Mount Vesuvius. Hippocrates (460–377 B.C.) was probably the first to describe how cow’s milk (CM) could cause gastric upset and hives, proposing dietetic measures including both treatment and prevention for CM allergy.

Dysfunction of innate immunity and associated pathology in neonates

The neutrophils and complement system are the critical elements of innate immunity mainly due to participation in the first line of defense against microorganisms by means of phagocytosis, lysis of bacteria and activation of naive B-lymphocytes. In this report we provide an overview of the up to date information regarding the neutrophil and complement system's functional ability in newborn infants in association with the maternal conditions that exist during the intrauterine stage, gestational age and post-neonatal pathology. The neonates' capacity to control the neutrophil and complement protein activation process has also been discussed because of the evidence that uncontrolled activation of these immune elements provides a significant contribution to the tissue damage and subsequent pathology. The authors are confident that despite the many unanswered questions this review updates their knowledge and points the need for further research to clarify the role of the age-associated dysfunction of neutrophils and complement system in the infection and inflammation related pathology of newborn infants.

Construction and analysis of variants of a polyvalent Lyme disease vaccine: approaches for improving the immune response to chimeric vaccinogens

There is currently no Lyme disease vaccine commercially available for use in humans. Outer surface protein C (OspC) of the Borrelia has been widely investigated as a potential vaccinogen. At least 38 OspC types have been defined. While the antibody response to OspC is protective, the range of protection is narrow due to the localization of protective epitopes within OspC type-specific domains. To develop a broadly protective vaccine, we previously constructed a tetravalent chimeric vaccinogen containing epitopes from OspC types A, B, K, and D. While this construct elicited bactericidal antibody against strains bearing each of the four OspC types, its solubility was low, and decreasing IgG titer to epitopes near the C-terminus of the construct was observed. In this report, construct solubility and immunogenicity were increased by dialysis against an Arg/Glu buffer. We also demonstrate the immunogenicity of the construct in alum. To further optimize epitope-specific immune responses, several constructs were generated with differing epitope organization or with putative C-terminal protective motifs. Analyses of murine antibody titers and isotype profiles induced by these constructs revealed that while the C-terminal tags did not enhance antibody titer, specific epitope reorganization and reiteration did. These analyses provide important information that can be exploited in the development of chimeric vaccinogens in general.

Hybridoma passage in vitro may result in reduced ability of antimannan antibody to protect against disseminated candidiasis

We previously reported the enhanced resistance of monoclonal antibodies B6.1 (an immunoglobulin M [IgM]) and C3.1 (an IgG3) against experimental candidiasis. Both MAbs recognize the same fungal epitope. We have since found that a highly passaged B6.1 hybridoma (hp-B6.1) resulted in antibody that has little protective potential. The potential clinical applicability of the antibody and our interest in understanding antibody protection against candidiasis led us to investigate an explanation for this phenomenon. Antibody genetic structure of hp-B6.1, the original hybridoma clone (ori-B6.1) stored frozen since 1995, a subclone of hp-B6.1 that produces protective antibody, the IgG3-producing hybridoma, and a nonprotective IgG1-producing hybridoma were compared. Variable region gene sequences of heavy (V(H)) and light chains showed genetic instability of V(H) chains with only the hp-B6.1; the V(H) sequences from ori-B6.1 and the subclone were, however, identical. Activation-induced cytidine deaminase levels were greatest in the B6.1 hybridomas, which may explain the instability. The constant region CH3 domain remained unchanged, implying normal N-glycation and complement-fixing potential, and antibody binding affinities appeared unchanged. Complement fixation assays surprisingly showed that ori-B6.1 antibody fixes C3 more rapidly than does hp-B6.1 antibody. The V(H) region primary structure may affect complement activation, which could explain our result. Indeed, antibody from the hp-B6.1 subclone fixed complement like antibody from ori-B6.1. These results show that the greatest protection occurs when antimannan antibodies possess the dual abilities of recognizing the appropriate carbohydrate epitope and rapidly fixing complement; loss of the latter property results in the loss of protective potential by the antibody.

Importance of carbohydrate in the interaction of Tamm‐Horsfall protein with complement 1q and inhibition of classical complement activation

Tamm-Horsfall protein (THP) binds strongly to complement 1q (C1q), a key component of the classical complement pathway. The goals of this study were to determine whether THP altered the activation of the classical complement pathway and whether the carbohydrate portion of THP was involved in this glycoprotein's binding to C1q and alteration of complement activation. The ability of THP to prevent complement activation in diluted serum or plasma incubated at 37 degrees C was assessed using both a haemolytic assay with antibody-sensitized sheep RBC and a C4d ELISA. Both these methods showed that THP inhibited activation of the classical complement pathway in a dose-dependent manner. Glycosidases were used to remove most of the carbohydrate from THP. This partially deglycosylated THP bound human IgG with a higher affinity (KD1 = 1.4 nmol/L; KD2 = 0.31 micromol/L) than did intact THP (KD1 = 33.4 nmol/L; KD2 = 31.0 micromol/L). An ELISA showed that removal of carbohydrate from THP reduced, but did not eliminate, the ability of this protein to inhibit binding of C1q to intact THP. Haemolysis assays using antibody-sensitized sheep RBC showed that removal of THP carbohydrate eliminated the ability of THP to protect against complement activation. In conclusion, THP inhibited the activation of the classical complement pathway that occurred in diluted serum or plasma. The carbohydrate moieties of THP appeared to be important in this inhibitory activity.

Gene expression profiling of the effects of intravenous immunoglobulin in human whole blood

Intravenous immunoglobulin (IVIG) is involved in many complex mechanisms that act in synergy including expression and function of Fc receptors, complement activation, the cytokine network, interaction with the anti-idiotypic network and modulation of B and T cell activation. To gain insight into the early effects of IVIG on this broad range of activities at the gene level we performed DNA microarray analysis. Human whole blood was incubated in vitro for 4 h followed by extraction of RNA which was hybridized to a chip containing 8793 genes. About 75 upregulated genes and 21 downregulated genes were identified using a cut off for the false discovery rate of 5%. These genes are associated with a wide range of cellular immune functions in line with the broad mechanism of action of IVIG. A striking upregulation of a series of genes coding for chemokines was measured. This finding was confirmed at the protein level as pharmacologically relevant concentrations of CXCL9 and CXCL10 were measured in serum. Interestingly, IVIG shows a partial overlap of its gene expression program with lipopolysaccharide. Our data suggests multiple hypotheses regarding the pharmacology of IVIG that must be validated by complementary studies.

The merits of in vitro versus in vivo modeling in investigation of the immune system

Immunity is vital for determining self and for the recognition and swift eradication of foreign antigens without harming the host. Innate immunity developed in metazoan, multi-cellular organisms under overwhelming selection pressure of invasive microbes and, although imperfect, has performed admirably to enable the evolution of higher eukaryotes. Adaptive immunity developed within an existing innate immune system to more effectively eradicate foreign antigens, whether from pathogens, malignant cells, or microbial toxins, such that repeated stimulations with foreign antigens are more efficiently excluded. Investigation of the immune system requires both in vivo and in vitro experimentation, not only because of the inherent complexity of immunity and the required pertinence of using higher mammals to not falsely disrupt the immune system, but also to use isolates of the specific cellular and humoral components to determine function, signal transduction, and a possible role of these constituents without the complexity and redundancy of immunity in intact animals. The hypotheses of well-designed in vitro experiments must also be tested in intact in vivo models to determine relevance and to discard artifactual findings secondary to the in vitro environment. The following review outlines the basic constituents and functions of both adaptive and innate immunity to demonstrate the importance of both in vivo and in vitro investigation of immunity in our attempt to define host defense and to decrease morbidity and mortality in humans.

The mannose-binding lectin: a prototypic pattern recognition molecule

The innate immune system is comprised of a sophisticated network of recognition and effector molecules that act together to protect the host in the first minutes or hours of exposure to an infectious challenge. The mannose-binding lectin (MBL) is an evolutionary conserved circulating host defense protein that acts as a broad-spectrum recognition molecule against a wide variety of infectious agents. Target binding triggers the MBL pathway of complement activation. MBL can be considered conceptually as an 'ante-antibody' because it has a role in mammals during the lag period that is required to develop an antibody response against infectious agents. Additionally, there are MBL-like homologues in animals that lack adaptive immunity that activate a primitive complement system, and under these circumstances these MBL-like molecules play an analogous role to antibodies in higher animals. These molecules might be considered to be functional antecedents of antibodies. Recent work also indicates that MBL recognizes altered self-antigens, and as such MBL has a role that extends beyond a traditional role in first line host defense as it appears to play a role as a modulator of inflammation.

Genetic selection for high and low immune response in pigs: Effects on immunoglobulin isotype expression

Immunoglobulin (Ig) function varies by isotype and antibody activity is best mediated by isotypes most able to control the inciting infection. In pigs, a high ratio of IgG1:IgG2 is associated with resistance to disease caused by the extra-cellular bacterium Actinobacillus pleuropneumoniae. This ratio is controlled by type 1/type 2 cytokines in vitro, reflecting cell- (CMI) or antibody-mediated immune (AMI) responses, respectively. Animals were used which had been previously selectively bred for high (HIR) or low (LIR) combined AMI and CMI and had been immunized with hen eggwhite lysozyme (HEWL) in Quil A (days 0 and 14) while Bacillus Calmette Guérin was given on day 9. To test the hypothesis that lines do not differ in IgG isotype expression as antibody to HEWL, the ratio of anti-HEWL associated with IgG1 and IgG2 was determined at days 0, 9, 14 and 21. The ratio of IgG1:IgG2-associated antibody was always <1.0 indicating a type 1 response and differed significantly over time in HIR and LIR animals. After primary and secondary immunizations, the HIR animals' IgG1:IgG2-associated antibody ratio increased and approached 1 while for LIR animals the ratio decreased. Thus anti-HEWL antibody in HIR, but not LIR, approached balance in type 2:type 1 expression. Individual variation in immune response was frequently significant within each immune response group. Thus, proportional production of anti-HEWL antibody associated with IgG isotypes varies by individual and differs over time as a function of genotype in pigs selectively bred for HIR or LIR.

Immunoglobulin γ3-heavy-chain deposition disease: report of a case and relationship with hypocomplementemia

The authors describe a 54-year-old woman presenting with proteinuria, hematuria, and hypocomplementemia whose renal biopsy results showed diffuse increase in mesangial matrix and nodular formations in several glomeruli with the deposition of immunoglobulin gamma3-heavy-chain and complement components C1q and C3 in the glomeruli and on the tubular basement membranes, without associated light-chain deposits. Staining for the constant domains of gamma-heavy-chain showed a deletion of the first constant domain (CH1). These findings were consistent with those of gamma-heavy-chain deposition disease (gamma-HCDD). The patient was treated monthly with melphalan and prednisolone although a bone marrow aspirate did not show findings suggestive of plasmacytoma. Six courses of melphalan and prednisolone therapy resulted in a marked reduction of urinary protein excretion and marked rise of complement levels. The current case is the fourth HCDD patient reported featuring gamma3-heavy-chain deposition who showed severe hypocomplementemia and responded to chemotherapy with improved renal parameters and complement levels. A review of previously reported cases of HCDD showed that some but not all HCDD cases were associated with hypocomplementemia. The authors also discuss here the relationship of HCDD to hypocomplementemia.

Porcine Ig isotypes: function and molecular characteristics

In pigs, protection against the toxigenic extra-cellular bacterium Actinobacillus pleuropneumoniae was correlated with an increased IgG(1):IgG(2) ratio of haemolytic toxin-specific antibodies. In all species so far studied, IgG isotype expression is controlled by Type 1 (IFN-gamma, IL-12) and Type 2 (IL-4, IL-10) cytokines which dictate immune response polarization to cell-mediated (CMI) or antibody-mediated immunity (AMI), respectively. Thus, immunoglobulin (Ig) isotypes reflect Type 1 or Type 2 immune responses. Immunoglobulin isotype production by porcine B-cells cultured in the presence of recombinant porcine (rp) cytokines varies by individual, however pigs tend to generate a high IgG(1):IgG(2) ratio in response to rp IL-10 and the inverse in response to rp IFN-gamma or rp IL-12. Differential Ig isotype production should favor an isotype with a functional advantage to control the inciting infection and disease. However, functions of porcine Ig isotypes have not been described. To compare function of porcine IgM, IgG(1) and IgG(2) of defined specificity for hen eggwhite lysozyme (HEWL), Ig isotypes were affinity purified from serum by HEWL specificity and by isotype-specific mouse monoclonal antibodies. Their ability to activate complement (C') and to opsonize was tested in vitro. Porcine IgG(2) had greater guinea pig C' activating ability than did IgG(1). Neither isotype opsonized HEWL-conjugated sheep erythrocytes in vitro. Amino acid sequence analysis of IgG isotypes revealed that all subclasses have putative C' binding sites but that IgG(2a), IgG(2b) and IgG(4) were more flexible in the middle hinge region than IgG(1) and IgG(3) and would likely activate C' more efficiently. Thus, porcine IgG isotypes associated with resistance and susceptibility to disease also differ in their actual and predicted biological functions.

Control of immunoglobulin isotype production by porcine B-cells cultured with cytokines

Cytokines regulate immunoglobulin (Ig) isotype production following the Th1/Th2 paradigm, derived from studies of inbred mice. In pigs, it is not known which, if any, Ig isotypes may reflect a Th1/Th2 response. To evaluate this, purified porcine CD21(+) B-cells were co-cultured with Staphylococcus aureus Cowan strain 1 or Escherichia coli lipopolysaccharide as B-cell mitogens together with recombinant human IL-2, and recombinant porcine (rp) interferon (IFN)-gamma, IL-12 or IL-10. While the mitogens increased B-cell proliferation, cytokines had no additional effect. A quantitative competitive enzyme-immuno assay was used to measure concentrations of porcine IgM, IgG(1) and IgG(2) in B-cell culture supernatants. In vitro, porcine B-cells produced IgG(2), 106 +/- 17.3 microg/ml; IgG(1) 107 +/- 38.3 microg/ml and IgM 25.6 +/- 8.45 microg/ml. In some individuals, Th1 cytokines such as rpIFN-gamma and IL-12, enhanced IgG(2) in the face of low concentrations of IgG(1). Furthermore, individual responses, in some cases, tended to be diametrically opposed, reminiscent of previously documented categorical immune responses in pigs such that some individuals produced high concentrations of IgG(1) in response to the various doses of rp cytokines, while others produced lower concentrations. Pigs may generate a high IgG(1):IgG(2) ratio in response to rpIL-10, and possibly to other Th2-associated cytokines. However, B-cell response to rp cytokines in vitro exhibits marked variation by pig, a feature that is likely a function of highly variable individual genotypes and their interaction with complex environments.

Large-scale comparison of experimental adjuvants with herpes simplex virus vaccine reveals a correlation of protection with IgG2a and IgG2b responses

The potential of a large number of commercial and experimental adjuvant preparations to enhance the immunogenicity of an HSV-1 glycoprotein subunit vaccine was investigated. Evaluation was based on toxicity, HSV-specific antibody production, and protection against lethal challenge. All adjuvants tested increased the titer of antigen specific Ig levels when compared to subunit vaccine alone. However, following challenge, a broad range of protective responses were noted. Statistically significant correlations were observed between IgG antibody levels post immunization and the observed protection and these were particularly associated with antibodies of the IgG2a and IgG2b subclasses. The results emphasize the requirement of adjuvants for vaccine formulation when using subunit preparations, and demonstrate that the magnitude and efficacy of the induced immune response varies greatly with the choice of adjuvant.

Il-4 therapy prevents the development of proteinuria in active Heymann nephritis by inhibition of Tc1 cells

The role of IL-4, a key Th2 cytokine, in promoting or inhibiting active Heymann nephritis (HN) was examined. HN is induced by immunization with Fx1A in CFA, and proteinuria in HN is associated with subepithelial IgG and C3 deposition and infiltration of CD8(+) T-cytotoxic 1 (Tc1) cells and macrophages into glomeruli, as well as induction of Abs to Crry. Treatment with rIL-4 from the time of Fx1A/CFA immunization stimulated an earlier IgG1 response to Fx1A, induced anti-Crry Abs, and up-regulated IL-4 mRNA in lymphoid tissue, but did not alter proteinuria. Treatment with MRCOx-81, an IL-4-blocking mAb, resulted in greater proteinuria, which suggests endogenous IL-4 regulated the autoimmune response. Delay of rIL-4 treatment until 4 wk post-Fx1A/CFA immunization and just before the onset of proteinuria prevented the development of proteinuria and reduced Tc1 cell infiltrate in glomeruli. Delayed treatment with IL-4 had no effect on titer or isotype of Abs to Fx1A or on Ig, C3, and C9 accumulation in glomeruli. Treatment with rIL-13, a cytokine that alters macrophage function such as rIL-4, but has no direct effect on T or B cell function, reduced glomerular macrophage infiltrate, but did not prevent proteinuria or CD8+ T cell infiltrate. Anti-Crry Abs were paradoxically only induced with rIL-4 therapy, not in HN controls with proteinuria. It was concluded that the rIL-4 effect was probably by inhibition of Tc1 cells, which normally mediate the glomerular injury that results in proteinuria.

Differential inhibitory effects of intravenous immunoglobulin preparations on HLA-alloantibodies in vitro

BACKGROUND

Treatment of allosensitized patients with intravenously administered pooled immunoglobulin preparations (IVIG) may lead to a long-lasting reduction of anti-HLA alloantibody titers. An inhibitory response of IVIG preparations on lymphocytotoxicity is suggested to depend on IgG and to predict a successful reduction of anti-HLA alloantibodies upon the administration of high-dose IVIG in vivo.

METHODS

In this study, we evaluated different IVIG preparations for their in vitro inhibitory capacity on lymphocytotoxicity and binding of anti-HLA alloantibodies to purified HLA antigens. For that purpose sera from 24 highly sensitized patients awaiting kidney transplantation and serological HLA testing reagents were used. Panel-reactive antibody (PRA) determinations using standard complement-dependent cytotoxicity testing and anti-HLA alloantibody determination by ELISA were carried out in the presence and absence of 50% (v/v) IVIG.

RESULTS

The addition of IgG-containing IVIG preparations gave only a moderate inhibitory response judging from the average decrease of PRA levels (absolute DeltaPRA range: -2% to 16%), whereas the largest inhibition of lymphocytotoxicity was seen after the addition of IgM/IgA-containing IVIG preparations (absolute DeltaPRA range: 19% to 44%). For both IgG and IgM/IgA-containing IVIG preparations, the reduction of lymphocytotoxicity occurred in a dose-dependent fashion without a preference for particular anti-HLA class I antibody specificities. Significantly lower inhibitory effects on anti-HLA antibody reactivity were observed when the effects of IVIG preparations were monitored by ELISA (absolute DeltaPRA range: 7% to 22%).

CONCLUSIONS

Our data suggest that the immunomodulatory capacity is largely caused by the IgM/IgA fraction of IVIG when analyzed by lymphocytotoxicity. The different effect on ELISA versus complement-dependent cytotoxicity testing suggests that interactions of IVIG with complement rather than anti-idiotypic antibodies may contribute to the inhibitory effects of IVIG in vitro.

Intravenous immunoglobulin prevents experimental autoimmune myositis in SJL mice by reducing anti-myosin antibody and by blocking complement deposition

High-dose intravenous immunoglobulin (IVIG) therapy has been effective in many autoimmune and systemic inflammatory diseases including polymyositis (PM) and dermatomyositis (DM). In the present study we evaluated the efficacy of IVIG using experimental models of PM and DM. An experimental autoimmune myositis (EAM) model was produced in SJL/J mice by an immunization with rabbit myosin B (MB) fraction. In this model, the plasma level of anti-MB antibody was elevated, and mouse IgG and complement C3 were deposited in the muscle fibres. Administration of IVIG dose-dependently reduced the incidences of necrotic and inflammatory changes in the skeletal muscle. IVIG treatment also decreased the elevation of anti-MB antibody level, as well as the deposition of IgG and C3. We next evaluated the effect of IVIG in adoptive EAM mice made by an intravenous injection of lymph node cells previously stimulated with MB. Adoptive EAM mice showed similar lesions in skeletal muscle as EAM mice and IVIG inhibited the lesion development. In vitro experiments demonstrated that IVIG inhibited complement-mediated lysis of human erythrocytes sensitized with anti-human erythrocyte antibodies. The binding of C1q, C4 and C3 to the same cells was also inhibited by IVIG. Taken together these findings suggest that IVIG prevents the development of myositis in EAM and adoptive EAM models by several mechanisms, such as reducing anti-myosin antibody and by blocking complement activation. Our present findings might account for the clinical efficacy of IVIG in PM and DM patients.

Ellipsometric in vitro studies on the activation of complement by human immunoglobulins M and G after adsorption to methylated silicon

Human serum immunoglobulin M (IgM) or human immunoglobulin G (IgG) were adsorbed to dichlorodimethyl silane (DDS) treated silicon. Subsequently, the model surfaces were incubated in normal-, complement factor 1q (C1q)-complement factor B or complement factor 2 (C2)-depleted human sera at 37 degrees C for up to 1.5 h. The serum deposition and binding of selected polyclonal complement antibodies into this layer were then quantified by null ellipsometry. Both types of precoated surfaces bound large amounts of anti-complement factor 3c (anti-C3c), anti-properdin and anti-C3d, after incubation in normal serum. In contrast to IgG coated surfaces, IgM coated surfaces bound no anti-C1q after the serum incubations and no anti-C3c deposition lag time was observed after incubations in EGTA serum. Upon immersions of IgM coated surfaces in the different sera, a rapid complement activation via a C1q factor B, and Ca(2+)-independent, but C2 dependent pathway, was indicated. When IgM was instead immobilized to APTES/glutaraldehyde surfaces, anti-C3c deposition was lower after incubations in EGTA than normal serum. The results suggest that, under the present experimental conditions, human IgM and IgG activate the complement system differently.

Phenotypic and functional properties of gamma delta T cells from patients with Guillain Barré syndrome

In this study we have examined the phenotypic and functional properties of circulating gamma delta T cells in patients with Guillain Barre syndrome (GBS), in normal healthy controls, and in patients with active multiple sclerosis (MS). Cells expressing the Vdelta2 T cell receptor showed elevated expression of the C-lectin receptor NKRP1A in both GBS and MS, suggestive of an activated state. However, in patients with GBS these cells failed to respond to pyrenil-pyrophosphate derivatives and Vdelta2 + T cell clones derived from these patients released lower levels of IFNgamma than Vdelta2 + clones derived from controls and MS patients. In contrast, in patients with GBS the Vdelta1 + subset was expanded, showed elevated expression of NKRPIA and Vdelta1 + clones derived from these patients secreted high levels of IL-4. Our findings of expanded NKRP-1A +, IL-4-producing Vdelta1 T cells in the GBS patients suggests the possibility that these cells are activated by the recognition of non-protein antigens in an MHC-unrestricted manner and contribute to the humoral response to glycolipids that is a hallmark of this disease.

Killing of Streptococcus pneumoniae by capsular polysaccharide-specific polymeric IgA, complement, and phagocytes

The role of IgA in the control of invasive mucosal pathogens such as Streptococcus pneumoniae is poorly understood. We demonstrate that human pneumococcal capsular polysaccharide-specific IgA initiated dose-dependent killing of S. pneumoniae with complement and phagocytes. The majority of specific IgA in serum was of the polymeric form (pIgA), and the efficiency of pIgA-initiated killing exceeded that of monomeric IgA-initiated killing. In the absence of complement, specific IgA induced minimal bacterial adherence, uptake, and killing. Killing of S. pneumoniae by resting phagocytes with immune IgA required complement, predominantly via the C2-independent alternative pathway, which requires factor B, but not calcium. Both S. pneumoniae-bound IgA and complement were involved, as demonstrated by a 50% decrease in killing with blocking of Fcalpha receptor (CD89) and CR1/CR3 (CD35/CD11b). However, IgA-mediated killing by phagocytes could be reproduced in the absence of opsonic complement by pre-activating phagocytes with the inflammatory products C5a and TNF-alpha. Thus, S. pneumoniae capsule-specific IgA may show distinct roles in effecting clearance of S. pneumoniae in the presence or absence of inflammation. These data suggest mechanisms whereby pIgA may serve to control pneumococcal infections locally and upon the pathogen's entry into the bloodstream.

The covalent interaction of C3 with IgG immune complexes

Antigens (Ags) are converted into immune complexes (antigen-antibody complexes, IC) as soon as they encounter their specific antibodies (Abs). In fluids containing complement, the process of IC formation and fixation of complement components occur simultaneously. Hence, the formation of Ag-Ab-complement complexes is the normal way of eliminating Ags from a host. C3b-C3b-IgG covalent complexes are immediately formed on interaction of serum C3 with IgG-IC. These C3b-C3b dimers constitute the core for the assembly of C3/C5-convertase on the IC, which are subsequently converted into iC3b-iC3b-IgG by the complement regulators. These complexes are detected on SDS-PAGE by two bands of molecular composition, C3alpha65-C3alpha43 (band A) and C3alpha65-heavy chain of the Ab (band B), which correspond to C3b-C3b and C3b-IgG covalent interaction respectively, and that identify opsonized IC (C3b-IC). C3b can attach to Fab and Fc regions of the Ab molecule with similar efficiency. The presence of multiple C3b binding regions on IgG is considered an advantageous characteristic that facilitates the elimination of Ags in the form of C3b(n)-IC. Ab molecules on the IC recognize the Ag, and also serve as a very good acceptor for C3b binding. In this way, Ags, even if they have no acceptor sites for C3b, can be efficiently processed and removed. When C3 is activated in serum by IC or other activators, secondary C3b-IgG covalent complexes are generated, with bystander monomeric circulating IgG, and thus constitute, physiological products of complement activation. These complexes gain importance when IgG concentration is extremely high as in cases of infusion of intravenous IgG (IVIG) in several pathologies. The covalent attachment of activated complement C3 (C3b, iC3b, C3 d,g) to Ags or IC links innate and adaptative immunity by targeting Ags to different cells of the immune system (follicular dendritic cells, phagocytes, B cells). Hence C3b marks Ags definitively, from the earliest contact with the innate immune system until their complete elimination from the host.

Characterization of human xenoreactive antibodies in liver failure patients exposed to pig hepatocytes after bioartificial liver treatment: an ex vivo model of pig to human xenotransplantation

BACKGROUND

There are limited experimental data on the nature of the humoral response elicited in humans against pig antigens. In this study, we have examined the xenoantibody (XAb) response in eight patients with acute liver failure exposed to pig hepatocytes after treatment with the bioartificial liver (BAL).

METHODS

Patients' plasma samples obtained before and after BAL treatment were tested for IgM and IgG XAbs, IgG subclasses, and XAb cytotoxicity, using enzyme-linked immunosorbent assay and flow-cytometric assays. The characterization of pig aortic endothelial cell (PAEC) surface xenoantigens was analyzed by immunoprecipitation.

RESULTS

We observed by day 10, a strong anti-pig IgG and IgM XAb response in patients undergoing two or more BAL treatments, with a significant increase in all the IgG subclasses; in contrast, XAb titers did not change if the patients received only one BAL treatment. The majority of the XAbs produced to porcine antigens were primarily specific for the alphaGal epitope. Both IgG and IgM XAbs were cytotoxic to PAECs, and the cytotoxic activity of IgG was associated with high levels of IgG1 and IgG3 subclasses, known to be efficient on complement activation. The characterization of porcine surface antigens demonstrated that IgM human XAbs, before and after BAL exposure, recognized xenoantigens on PAECs with similar molecular weights, suggesting that the same population of XAbs were present in the patients before and after exposure to pig antigens.

CONCLUSIONS

Repetitive exposure of humans to porcine antigens after BAL treatment, results in a strong IgG and IgM XAb responses that are primarily directed against the alphaGal epitope. These XAbs are cytotoxic to PAECs and the IgG toxicity correlates with high IgG1 and IgG3 levels. Our data also suggest that no new XAb specificity emerges after porcine exposure.

High-dose intravenous immunoglobulin treatment activates complement in vivo

Several complement modulating effects of high-dose intravenous immunoglobulins (IVIG) have been proposed from in vitro studies and experimental animal models. However, the in vivo effects of IVIG on plasma complement in humans are yet not known. We have investigated the in vivo effects of IVIG on complement in seven women with unexplained recurrent spontaneous abortion who were without evidence of autoimmune disease. Samples were obtained before and after the very first infusion of IVIG. There was a marked increase in immunoglobulin G (IgG) from (median and range) 12.4 (9.4-15.9) to 26.8 (22.4-30.0) g/l but no change in immunoglobulin A (IgA) or immunoglobulin M (IgM). A significantly increased complement activation was demonstrated using neoepitope-specific enzyme immunoassays to the activation products C3bc (median increased from 9.8 to 31.2 AU/ml), Bb (0.66-1.66 g/ml), C5a (10.5-12.7 ng/ml), and TCC (0.81-2.19 AU/ml) (P = 0.015 for all). There were no changes in antigenic concentrations of individual complement components or regulators (C1q, C4, C3, C1-inhibitor, C4b-binding protein) and no decrease in complement haemolytic activity (classical and alternative CH50), which were all within the normal range. The classical pathway activation products C1rs/C1-inhibitor complexes, C4bc and C4d were elevated in all patients before IVIG treatment and did not change significantly during treatment. In conclusion, IVIG induced a significant activation of complement in vivo.

Immune complex-like moieties in immunoglobulin for intravenous use (i.v.Ig) bind complement and enhance phagocytosis of human erythrocytes

Treatment with i.v.Ig can, on rare occasions, lead to detrimental effects such as enhanced erythrocyte sequestration and an increase in serum immune complexes with inflammatory sequellae such as exacerbation of glomerular nephritis. In this study, i.v.Ig (Sandoglobin) was examined for complement binding moieties which resemble immune complexes and can mediate the binding of IgG and C'3b to human erythrocytes via CR1 and enhance erythrocyte susceptibility to sequestration. Sephacryl S-200 HR separated i.v.Ig into two fractions: monomeric IgG (74%) and larger complexes of the molecular weight of an IgG dimer or greater (> or = 300 kD) (26%). In the presence of complement, the 'dimers' bound to human erythrocytes, rendering them susceptible to phagocytosis in vitro. Removal of erythrocyte-specific isoantibodies from the i.v.Ig had no effect on 'dimer' binding to the erythrocytes. Monomeric IgG contained virtually no complement-activating, erythrocyte-binding activity. Erythrocyte binding of complement-bearing IgG 'dimers' and subsequent phagocytosis resembles the binding of complement-bearing immune complexes to erythrocyte CR1. Exposure to Factor I leads to the release of complement-bearing IgG 'dimers' from erythrocyte CR1 and to the abrogation of erythrophagocytosis. Binding of complement-bearing IgG 'dimers' to the erythrocyte is blocked by To5, a CR1-specific monoclonal antibody.

Anti-FcepsilonRIalpha autoantibodies in autoimmune-mediated disorders. Identification of a structure-function relationship

Anti-FcepsilonRIalpha autoantibodies (autoAbs) occur and may be of pathogenetic relevance in a subset of chronic urticaria (CU) patients. To analyze the prevalence and magnitude of the humoral anti-FcepsilonRIalpha response in cohorts of CU patients compared with individuals suffering from classic skin- related (auto)immune diseases, we developed an ELISA system for the measurement of anti-FcepsilonRIalpha autoAbs in nonfractionated serum samples. Results obtained using this assay correlated well with those generated by Western blotting. We found IgG anti-FcepsilonRIalpha autoreactivity in 38% of CU patients but not in atopic dermatitis patients, psoriatics, or healthy individuals. We frequently detected anti-FcepsilonRIalpha autoAbs in pemphigus vulgaris (PV, 39%), dermatomyositis (DM, 36%), systemic lupus erythematosus (SLE, 20%), and bullous pemphigoid (BP, 13%). While the autoAb titers in DM, SLE, BP, and PV were similar to those encountered in CU patients, only anti-FcepsilonRIalpha+ CU serum specimens displayed pronounced histamine-releasing activity. The anti-FcepsilonRIalpha autoAbs in CU patients belong predominantly to the complement-fixing subtypes IgG1 and IgG3, whereas in DM, PV, and BP, they were found to be mainly of the IgG2 or IgG4 subtype. Complement-activating properties of anti-FcepsilonRIalpha autoAbs can indeed be of pathogenetic relevance, because C5a receptor blockade on basophils as well as decomplementation reduced drastically the histamine-releasing capacity of most anti-FcepsilonRIalpha-reactive CU sera. As a consequence, therapeutic efforts in CU should aim at altering not only the quantity but also the complement-activating properties of IgG anti-FcepsilonRIalpha autoAbs.

Pathogenesis of autoimmunity in alphabeta T cell-deficient lupus-prone mice

Murine lupus in MRL mice has been strongly attributed to alphabeta T cell-dependent mechanisms. Non-alphabeta T cell-dependent mechanisms, such as gammadelta T cells, have been shown to drive antibody and autoantibody production, but they have not been considered capable of inducing end-organ disease. Here, we have expanded upon the findings of such previous work by examining the mechanism and extent of end-organ disease attainable via gammadelta T cells and/or non-alphabeta T cell-dependent mechanisms, assessing two prototypical lupus lesions, renal and skin disease, in TCR alpha -/- MRL mice that possessed either functional or defective Fas antigen (Fas + or lpr). Observed to 1 year of age, TCR alpha -/- MRL mice developed disease characterized by increased mortality, overt renal disease and skin lesions. While delayed in onset and/or reduced in severity compared with TCR alpha +/+ MRL/lpr animals, renal and skin lesions in alphabeta T cell-deficient animals were clearly increased in severity compared with age-matched control non-autoimmune mice. In contrast to TCR alpha +/+ MRL mice, whose disease reflected pan-isotype immune complex deposition with significant complement fixation, renal disease in TCR alpha -/- MRL animals reflected predominantly IgG1 immune complex deposition, with poor complement fixation. Thus, this study demonstrates conclusively that non-alphabeta T cell-dependent mechanisms can induce renal and skin injury in murine lupus, but at least in the kidney, only via humoral autoimmunity of a relatively non-pathological isotype which results in the delayed onset of end-organ damage.

Modification of humoral responses by the combination of leflunomide and cyclosporine in Lewis rats transplanted with hamster hearts

BACKGROUND

Vigorous antibody-mediated responses prevent the successful engraftment of hamster hearts transplanted into Lewis rats. Early antibody responses mediating acute rejection of the xenograft are T cell-independent and resistant to the T-cell immunosuppressant, cyclosporine (CsA). Immunosuppression with the combination of leflunomide plus CsA completely prevents xenograft rejection, but when such immunosuppression is stopped the hamster heart is rejected by a process that we term late xenograft rejection. We report here on some of the immunological features of late xenograft rejection.

METHODS

Lewis rats transplanted with hamster hearts were treated with leflunomide (5 mg/kg/day by gavage) for 14-21 days and CsA (20 mg/kg/day by gavage) continuously from the day of transplant. Serum was harvested and the functional activities of the xenoreactive antibodies were quantitated by in vivo passive transfer of sera, flow cytometry, in vitro C3 deposition assays, and Western blotting.

RESULTS

CsA alone prevented late xenograft rejection and the accompanying production of xenoreactive antibodies. The xenoreactive antibodies accompanying acute or late xenograft rejection were predominantly IgM, but only serum from rats undergoing acute xenograft rejection was able to induce hyperacute rejection. The ability of serum to induce hyperacute rejection correlated with its ability to induce C3 deposition on hamster lymphocytes in vitro. The repertoire of hamster antigens recognized by IgM in the serum of rats undergoing late xenograft rejection is more restricted than that of IgM in the serum of rats undergoing acute xenograft rejection. We additionally demonstrate that long-term graft survival is not dependent on graft accommodation.

CONCLUSIONS

These studies demonstrate that a brief treatment with the combination of leflunomide and CsA profoundly modifies the humoral xenoreactivity in the recipient, converting it from a T-independent into a T cell-dependent response. Differences in functional activity of sera from acute or late xenograft rejection suggest that antigenic specificity defines the ability of IgM to induce complement activation and hyperacute rejection.

Mechanisms of acantholysis in pemphigus foliaceus

Pemphigus foliaceus (PF) is a dermatosis characterized by subcorneal vesicles and pathogenic IgG autoantibodies against desmoglein 1. PF IgG passively transferred into neonatal mice induces a blistering disease that duplicates the key findings of PF. In this study we have used this animal model to investigate the role of complement and IgG valence in triggering blister formation. In the passive transfer experiments, we found that PF IgG, as well as the F(ab')2 and Fab fragments, was capable of inducing the typical subcorneal blistering disease in both complement-deficient and complement-sufficient mice. Moreover, the disease activity in these mice correlated well with the dose of IgG or its proteolytic fragments injected in the animals. We conclude that neither complement activation nor IgG-mediated cell surface antigen crosslinking is required for the induction of acantholysis in the experimental PF model.

Beta-amyloid peptides initiate the complement cascade without producing a comparable effect on the terminal pathway in vitro

Activation of the classical complement cascade by beta-amyloid peptides has been hypothesized to underlie the neurodegeneration observed in Alzheimer's diseased brains. In this study, various lots of synthetic beta-amyloid peptides, A beta(1-40), A beta(1-42), and A beta(25-35), were tested for their ability to activate both early complement cascade events and formation of the membrane attack complex through terminal pathway activation. Unlike recent reports which did not assess activation of complement terminal pathway, we found that concentrations of beta-amyloid which activated early cascade events, to an extent comparable to aggregated IgG, failed to elicit formation of comparable levels of membrane attack complex.

New protein engineering approaches to multivalent and bispecific antibody fragments

Multivalency is one of the hallmarks of antibodies, by which enormous gains in functional affinity, and thereby improved performance in vivo and in a variety of in vitro assays are achieved. Improved in vivo targeting and more selective localization are another consequence of multivalency. We summarize recent progress in engineering multivalency from recombinant antibody fragments by using miniantibodies (scFv fragments linked with hinges and oligomerization domains), spontaneous scFv dimers with short linkers (diabodies), or chemically crosslinked antibody fragments. Directly related to this are efforts of bringing different binding sites together to create bispecific antibodies. For this purpose, chemically linked fragments, diabodies, scFv-scFv tandems and bispecific miniantibodies have been investigated. Progress in E. coli expression technology makes the amounts necessary for clinical studies now available for suitably engineered fragments. We foresee therapeutic advances from a modular, systematic approach to optimizing pharmacokinetics, stability and functional affinity, which should prove possible with the new recombinant molecular designs.

Roles of interferon-gamma and interleukin-4 in murine lupus

The systemic autoimmune syndrome of MRL/Mp-lpr/lpr (MRL/lpr) mice consists of severe pan-isotype hypergammaglobulinemia, autoantibody production, lymphadenopathy, and immune complex-associated end-organ disease. Its pathogenesis has been largely attributed to helper alphabeta T cells that may require critical cytokines to propagate pathogenic autoantibody production. To investigate the roles of prototypical Th1 and Th2 cytokines in the pathogenesis of murine lupus, IFN-gamma -/- and IL-4 -/- lupus-prone mice were generated by backcrossing cytokine knockout animals against MRL/lpr breeders. IFN-gamma -/- animals produced significantly reduced titers of IgG2a and IgG2b serum immunoglobulins as well as autoantibodies, but maintained comparable levels of IgG1 and IgE in comparison to cytokine-intact controls; in contrast, IL-4 -/- animals produced significantly less IgG1 and IgE serum immunoglobulins, but maintained comparable levels of IgG2a and IgG2b as well as autoantibodies in comparison to controls. Both IFN-gamma -/- and IL-4 -/- mice, however, developed significantly reduced lymphadenopathy and end-organ disease. These results suggest that IFN-gamma and IL-4 play opposing but dispensable roles in the development of lupus-associated hypergammaglobulinemia and autoantibody production; however, they both play prominent roles in the pathogenesis of murine lupus-associated tissue injury, as well as in lpr-induced lymphadenopathy.

Temporal studies on the deposition of complement on human colostrum IgA and serum IgG immobilized on methylated silicon

The temporal deposition of selected complement proteins from human serum onto immobilized human colostrum immunoglobulin (Ig)A and human IgG on hydrophobic silicon was studied by ellipsometry-antibody techniques after incubations at 37 degrees C for up to 1 h. In parallel experiments the serum soluble iC3b, C4d, and Bb were detected by enzyme-linked immunosorbent assay techniques. The IgA-coated surfaces showed activation via the alternative pathway, and displayed a lag phase in the deposition of increased amounts of serum proteins, and anti-C3c and antiproperdin. Anti-IgG, -C1q, -C4, -factor H and -factor B were not deposited at any time to IgA surfaces. Upon coating of the surface with IgG, the classical pathway was rapidly activated and bound, then anti-C3c, antiproperdin, and after short serum incubation times, also anti-C1q and anti-IgG. When factor B-depleted or heat-treated sera were used, the observation was that properdin deposited onto IgG-coated surfaces from both. Ellipsometry and antibody techniques offer a convenient and rapid way to indicate the activation of the complement system on solid surfaces and facilitates a time-resolved determination of the activation pathway(s).

Characterization of complement C3, C4, and factor B molecules in human bile

We performed molecular analysis of complement components (C3, C4, and factor B) in human bile by sodium dodecyl sulfate-polyarylamide gel electrophoresis (SDS-PAGE) and immunoblotting. Complement C3 was detected as a molecule composed of a 115-kDa alpha-chain linked to a 70-kDa beta-chain by disulfide bonds, and C3 levels ranged from 45 to 650 micrograms/ml (n = 15). C4 was detected as a triple chain (98-kDa alpha-chain, 73-kDa beta-chain, and 33-kDa gamma-chain) molecule linked by disulfide bonds, and C4 levels ranged from 2.5 to 60 micrograms/ml. Factor B, a component of the alternative pathway, was also detected, as an intact form. Factor B levels ranged from 0.3 to 8.0 micrograms/ml. The sizes and subunit structures of complement components in human bile were compatible with those reported in human serum. The results of a hemolytic assay indicated that complement molecules in human bile were functionally active. These molecules may participate in local immune and inflammatory responses in the biliary tract.