Invariance and restriction toward a limited set of self-antigens characterize neonatal IgM antibody repertoires and prevail in autoreactive repertoires of healthy adults

Stereotyped patterns of somatic hypermutation in subsets of patients with chronic lymphocytic leukemia: implications for the role of antigen selection in leukemogenesis

Somatic hypermutation (SHM) features in a series of 1967 immunoglobulin heavy chain gene (IGH) rearrangements obtained from patients with chronic lymphocytic leukemia (CLL) were examined and compared with IGH sequences from non-CLL B cells available in public databases. SHM analysis was performed for all 1290 CLL sequences in this cohort with less than 100% identity to germ line. At the cohort level, SHM patterns were typical of a canonical SHM process. However, important differences emerged from the analysis of certain subgroups of CLL sequences defined by: (1) IGHV gene usage, (2) presence of stereotyped heavy chain complementarity-determining region 3 (HCDR3) sequences, and (3) mutational load. Recurrent, “stereotyped” amino acid changes occurred across the entire IGHV region in CLL subsets carrying stereotyped HCDR3 sequences, especially those expressing the IGHV3-21 and IGHV4-34 genes. These mutations are underrepresented among non-CLL sequences and thus can be considered as CLL-biased. Furthermore, it was shown that even a low level of mutations may be functionally relevant, given that stereotyped amino acid changes can be found in subsets of minimally mutated cases. The precise targeting and distinctive features of somatic hypermutation (SHM) in selected subgroups of CLL patients provide further evidence for selection by specific antigenic element(s).

The innate immune response of finfish--a review of current knowledge

The decline in the fisheries of traditional marine species has been an incentive for the diversification of today's aquaculture sector into the intensive rearing of many finfish species. The increasing interest in commercial farming of different finfish species is expected to result in similar environmental and husbandry-related problems as have been experienced in the development of the salmonid farming industry. An understanding of the biology of the fish species being cultured, in particular the immune response is important for improved husbandry and health management of the species. The innate immune system of fish has generated increasing interest in recent years and is now thought to be of key importance in primary defence and in driving adaptive immunity. This review focuses on key components (cellular and humoral) of the innate immune responses of different fish species of commercial importance.

Real and artificial immune systems: computing the state of the body

Here I present the idea that the immune system uses a computational strategy to carry out its many functions in protecting and maintaining the body. Along the way, I define the concepts of computation, Turing machines and system states. I attempt to show that reframing our view of the immune system in computational terms is worth our while.

Newborn humans manifest autoantibodies to defined self molecules detected by antigen microarray informatics

Autoimmune diseases are often marked by autoantibodies binding to self antigens. However, many healthy persons also manifest autoantibodies that bind to self antigens, known as natural autoantibodies. In order to characterize natural autoantibodies present at birth, we used an antigen microarray (antigen chip) to analyze informatically (with clustering algorithms and correlation mapping) the natural IgM, IgA, and IgG autoantibody repertoires present in 10 pairs of sera from healthy mothers and the cords of their newborn babies. These autoantibodies were found to bind to 305 different, mostly self, molecules. We report that in utero, humans develop IgM and IgA autoantibodies to relatively uniform sets of self molecules. The global patterns of maternal IgM autoantibodies significantly diverged from those at birth, although certain reactivities remained common to both maternal and cord samples. Because maternal IgG antibodies (unlike IgM and IgA) cross the placenta, maternal and cord IgG autoantibodies showed essentially identical reactivities. We found that some self antigens that bind cord autoantibodies were among the target self antigens associated with autoimmune diseases later in life. Thus, the obviously benign autoimmunity prevalent at birth may provide the basis for the emergence of some autoimmune diseases relatively prevalent later in life.

Dynamic stability in random and scale-free B-lymphocyte networks

One of the most intriguing features of the immune system is regulation: a limited response when perturbed repeatedly. We propose a minimal network model for immune regulation in a lymphocyte network containing two types of elements: B lymphocytes and ligands that bind to their receptors. Effective interactions between B cells, mediated by other components of the immune system can be excitatory or inhibitory. In our model, B cell clones and ligand species are represented by nodes, and interactions by links. We expect that, as in many complex systems, the connectivity distribution is broad, motivating study of the model on a scale-free network; for comparison we study the same dynamics on a random graph. We characterize the dynamics of the model and its response to perturbations. Our model reproduces several key features of immune system dynamics: regulation (saturation of response), and more rapid response upon repeated perturbation with the same agents. Our results suggest that a scale-free network of interactions contributes to the regulation and dynamics of the immune system.

Anti-endothelial cell antibodies from patients with limited cutaneous systemic sclerosis bind to centromeric protein B (CENP-B)

By using a quantitative immunoblotting technique on protein extracts of human macrovascular and microvascular endothelial cells, we have analyzed the self-reactive repertoires of IgG from 20 patients with limited cutaneous SSc, 40 patients with diffuse SSc and 60 age- and sex-matched healthy controls. Serum IgG from 15/20 patients with limited cutaneous SSc and anti-centromere antibodies bound to at least one of the two 75- and 85-kDa protein bands in the different endothelial cell extracts, whereas IgG from healthy controls or patients with diffuse SSc did not. N-terminal sequencing of the 75- and 85-kDa bands identified CENP-B as the sole antigen in both bands. Moreover, IgG from all of the SSc patients who recognized the 75- and/or 85-kDa bands bound to a full-length recombinant CENP-B protein as assessed by ELISA, whereas IgG from other SSc patients did not. The main target of anti-endothelial cell antibodies in patients with limited cutaneous SSc is the nuclear and ubiquitous protein CENP-B.

A high-affinity natural autoantibody from human cord blood defines a physiologically relevant epitope on the FcepsilonRIalpha

Natural Abs represent the indigenous immune repertoire and are thus present at birth and persist throughout life. Previously, human autoantibodies to the alpha domain of the high-affinity IgE receptor (FcepsilonRIalpha) have been isolated from Ab libraries derived from normal donors and patients with chronic urticaria. To investigate whether these anti-FcepsilonRIalpha Abs are present in the germline repertoire, we constructed a phage Fab display library from human cord blood, which represents the naive immune repertoire before exposure to exogenous Ags. All isolated clones specific to the FcepsilonRIalpha had the same sequence. This single IgM Ab, named CBMalpha8, was strictly in germline configuration and had high affinity and functional in vitro anaphylactogenic activity. Inhibition experiments indicated an overlapping epitope on the FcepsilonRIalpha recognized by both CBMalpha8 and the previously isolated anti-FcepsilonRIalpha Abs from autoimmune and healthy donors. This common epitope on FcepsilonRIalpha coincides with the binding site for IgE. Affinity measurements demonstrated the presence of Abs showing CBMalpha8-like specificity, but with a significantly lower affinity in i.v. Ig, a therapeutic multidonor IgG preparation. We propose a hypothesis of escape mutants, whereby the resulting lower affinity IgG anti-FcepsilonRIalpha Abs are rendered less likely to compete with IgE for binding to FcepsilonRIalpha.

Evidence that human autoimmune thrombocytopenia mediated by both immunoglobulin isotypes IgM and IgG is an independent disease entity

Autoimmune thrombocytopenic purpura (AITP) is a bleeding disorder caused by clonally restricted self-reactive antibodies with specificity for platelet glycoproteins. Anti-platelet autoantibodies in AITP mainly belong to the IgG class. The occurrence of anti-platelet autoantibodies of the IgM isotype has been reported, and AITP is partially mediated by antibodies of both isotypes, IgM and IgG. Using a technique of quantitative immunoblotting of immunoglobulins on self-tissues, followed by multiparametric statistical analysis of the data, we here demonstrate that patients with IgM- and IgG-mediated AITP are readily discriminated from patients with IgM-mediated AITP as well as from patients with IgG-mediated AITP at the basis of self-reactive antibody repertoires of isotypes IgM and IgG toward non-platelet antigens of human origin. Our data suggest that, in view of the important physiological functions of self-reactive antibody repertoires, human AITP mediated by both immunoglobulin isotypes IgG and IgM may be an independent disease entity. The role of autoantibody isotype for the pathophysiology of AITP might currently be underestimated, and diagnostic and therapeutic procedures in AITP might profit from considering autoantibody isotype more carefully.

Thymic commitment of regulatory T cells is a pathway of TCR-dependent selection that isolates repertoires undergoing positive or negative selection

The seminal work of Le Douarin and colleagues (Ohki et al. 1987; Ohki et al. 1988; Salaun et al. 1990; Coutinho et al. 1993) first demonstrated that peripheral tissue-specific tolerance is centrally established in the thymus, by epithelial stromal cells (TEC). Subsequent experiments have shown that TEC-tolerance is dominant and mediated by CD4 regulatory T cells (Treg) that are generated intrathymically by recognition of antigens expressed on TECs (Modigliani et al. 1995; Modigliani et al. 1996a). From these and other observations, in 1996 Modigliani and colleagues derived a general model for the establishment and maintenance of natural tolerance (MM96) (Modigliani et al. 1996b), with two central propositions: (1) T cell receptor (TCR)-dependent sorting of emergent repertoires generates TEC-specific Treg displaying the highest TCR self-affinities below deletion thresholds, thus isolating repertoires undergoing positive and negative selection; (2) Treg are intrathymically committed (and activated) for a unique differentiative pathway with regulatory effector functions. The model explained the embryonic/perinatal time window of natural tolerance acquisition, by developmental programs determining (1) TCR multireactivity, (2) the cellular composition in the thymic stroma (relative abundance of epithelial vs hemopoietic cells), and (3) the dynamics of peripheral lymphocyte pools, built by accumulation of recent thymic emigrants (RTE) that remain recruitable to regulatory functions. We discuss here the MM96 in the light of recent results demonstrating the promiscuous expression of tissue-specific antigens by medullary TECs (Derbinski et al. 2001; Anderson et al. 2002; Gotter et al. 2004) and indicating that Treg represent a unique differentiative pathway (Fontenot et al. 2003; Hori et al. 2003; Khattri et al. 2003), which is adopted by CD4 T cells with high avidity for TEC-antigens (Bensinger et al. 2001; Jordan et al. 2001; Apostolou et al. 2002). In the likelihood that autoimmune diseases (AID) result from Treg deficits, some of which might have a thymic origin, we also speculate on therapeutic strategies aiming at selectively stimulating their de novo production or peripheral function, within recent findings on Treg responses to inflammation (Caramalho et al. 2003; Lopes-Carvalho et al., submitted, Caramalho et al., submitted). In short, the MM96 argued that natural tolerance is dominant, established and maintained by the activity of Treg, which are selected upon high-affinity recognition of self-ligands on TECs, and committed intrathymically to a unique differentiative pathway geared to anti-inflammatory and antiproliferative effector functions. By postulating the intrathymic deletion of self-reactivities on hemopoietic stromal cells (THC), together with the inability of peripheral resident lymphocytes to engage in the regulatory pathway, the MM96 simultaneously explained the maintenance of responsiveness to non-self in a context of suppression mediating dominant self-tolerance. The major difficulty of the MM96 is related to the apparent tissue specificity of Treg repertoires generated intrathymically. This difficulty has now been principally solved by the work of Hanahan, Kyewski and others (Jolicoeur et al. 1994; Derbinski et al. 2001; Anderson et al. 2002; Gotter et al. 2004), demonstrating the selective expression of a variety of tissue-specific antigens by TECs, in topological patterns that are compatible with the MM96, but difficult to conciliate with recessive tolerance models (Kappler et al. 1987; Kisielow et al. 1988). While the developmentally regulated multireactivity of TCR repertoires (Gavin and Bevan 1995), as well as the peripheral recruitment of Treg among RTE (Modigliani et al. 1996a) might add to this process, it would seem that the establishment of tissue-specific tolerance essentially stems from the "promiscuous expression of tissue antigens" by TEC. The findings of AID resulting from natural mutations (reviewed in Pitkanen and Peterson 2003) or the targeted inactivation (Anderson et al. 2002; Ramsey et al. 2002) of the AIRE transcription factor that regulates promiscuous gene expression on TECs support this conclusion. The observations on the correlation of natural or forced expression of the Foxp3 transcription factor in CD4 T cells with Treg phenotype and function (Fontenot et al. 2003; Hori et al. 2003; Khattri et al. 2003) provided support for the MM96 contention that Treg represent a unique differentiative pathway that is naturally established inside the thymus. Furthermore, Caton and colleagues (Jordan et al. 2001), as well as several other groups (Bensinger et al. 2001; Apostolou et al. 2002), have provided direct evidence for our postulate that Treg are selected among differentiating CD4 T cells with high affinity for ligands expressed on TECs (Modigliani et al. 1996b). Finally, the demonstration by Caramalho et al. that Treg express innate immunity receptors (Caramalho et al. 2003) and respond to pro-inflammatory signals and products of inflammation (Caramalho et al., submitted) brought about a new understanding on the peripheral regulation of Treg function. Together with the observation that Treg also respond to ongoing activities of "naïve/effector" T cells--possibly through the IL-2 produced in these conditions--these findings explain the participation of Treg in all immune responses (Onizuka et al. 1999; Shimizu et al. 1999; Annacker et al. 2001; Curotto de Lafaille et al. 2001; Almeida et al. 2002; Shevach 2002; Bach and Francois Bach 2003; Wood and Sakaguchi 2003; Mittrucker and Kaufmann 2004; Sakaguchi 2004), beyond their fundamental role in ensuring self-tolerance (e.g., Modigliani et al. 1996a; Shevach 2000; Hori et al. 2003; Sakaguchi 2004; Thompson and Powrie 2004). Thus, anti-inflammatory and anti-proliferative Treg are amplified by signals that promote or mediate inflammation and proliferation, accounting for the quality control of responses (Coutinho et al. 2001). In turn, such natural regulation of Treg by immune responses to non-self may well explain the alarming epidemiology of allergic and AID in wealthy societies (Wills-Karp et al. 2001; Bach 2002; Yazdanbakhsh et al. 2002), where a variety of childhood infections have become rare or absent. Thus, it is plausible that Treg were evolutionarily set by a given density of infectious agents in the environment. With hindsight, it is not too surprising that natural Treg performance falls once hygiene, vaccination, and antibiotics suddenly (i.e., 100 years) plunged infectious density to below some critical physiological threshold. As the immune system is not adapted to modern clean conditions of postnatal development, clinical immunologists must now deal with frequent Treg deficiencies (allergies and AID) for which they have no curative or rational treatments. It is essential, therefore, that basic immunologists concentrate on strategies to selectively stimulate the production, survival, and activity of this set of lymphocytes that is instrumental in preventing immune pathology. We have argued that the culprit of this inability of basic research to solve major clinical problems has been the self-righteousness of recessive tolerance champions, from Ehrlich to some of our contemporaries. It is ironical, however, that none of us--including the heretic opponents of horror autotoxicus--had understood that self-tolerance, or its robustness at least, is in part determined by the frequency and intensity of the responses to non-self. In the evolution of ideas on immunological tolerance, the time might be ripe for some kinds of synthesis. First, conventional theory reduced self-tolerance to negative selection and microbial defense to positive selection, while the MM96 solution was the precise opposite: positive selection of autoreactivities for self-tolerance (Treg) and negative selection (of Treg) for ridding responses. In contrast, it would now appear that positive and negative selection of autoreactive T cells are both necessary to establish either self-tolerance or competence to eliminate microbes, two processes that actually reinforce each other in the maintenance of self-integrity. Second, V-region recognition has generally been held responsible for specific discrimination between what should be either tolerated or eliminated from the organism. In contrast again, it would now seem that both processes of self-tolerance and microbial defense (self/non-self discrimination) also operate on the basis of evolutionarily ancient, germ-line-encoded innate, nonspecific receptors (Medzhitov and Janeway 2000) capable of a coarse level of self/non-self discrimination (Coutinho 1975). It could thus be interesting to revisit notions of cooperativity between V-regions and such mitogen receptors, both in single cell functions (Coutinho et al. 1974) and in the system's evolution (Coutinho 1975, 1980) as well. After all, major transitions in evolution were cooperative (Maynard-Smith and Szathmary 1995).

Anti-endothelial cell antibodies in idiopathic and systemic sclerosis associated pulmonary arterial hypertension

BACKGROUND

It has previously been shown that IgG antibodies from patients with limited cutaneous systemic sclerosis (SSc) bind to specific microvascular endothelial cell antigens. Since patients with limited cutaneous SSc are prone to develop pulmonary arterial hypertension (PAH), and since endothelial cell activation is involved in the pathogenesis of idiopathic PAH (IPAH), a study was undertaken to examine the presence of anti-endothelial cell antibodies in patients with idiopathic or SSc associated PAH.

METHODS

PAH was confirmed by right heart catheterisation (mean pulmonary artery pressure at rest >25 mm Hg). Serum IgG and IgM reactivities were analysed by immunoblotting on human macrovascular and microvascular lung and dermal endothelial cells from patients with IPAH (n = 35), patients with PAH associated with SSc (n = 10), patients with diffuse (n = 10) or limited cutaneous (n = 10) SSc without PAH, and 65 age and sex matched healthy individuals.

RESULTS

IgG antibodies from patients with IPAH bound to a 36 kDa band in macrovascular endothelial cell extracts with a higher intensity than IgG from other patient groups and controls. IgG antibodies from patients with IPAH bound more strongly to a 58 kDa band in microvascular dermal endothelial cells and to a 53 kDa band in microvascular lung endothelial cells than IgG antibodies from other patients and controls. IgG antibodies from patients with limited cutaneous SSc with or without PAH, but not from other groups or from healthy controls, bound to two major bands (75 kDa and 85 kDa) in microvascular endothelial cells.

CONCLUSION

IgG antibodies from patients with idiopathic or SSc associated PAH express distinct reactivity profiles with macrovascular and microvascular endothelial cell antigens.

Heritable factors shape natural human IgM reactivity to Ro60/SS-A and may predispose for SLE-associated IgG anti-Ro and anti-La autoantibody production

Systemic lupus erythematosus (SLE) is characterized by various IgG autoreactivities, among which anti-Ro/SS-A is particularly pathology-associated and early detectable. SLE also shows significant familial aggregation, but genetic factors are not well understood and remain controversial for disease-associated IgG. Here we report that IgM anti-Ro showed a uniquely high degree of heritability in a study of SLE-affected families. Unlike IgM anti-La or anti-dsDNA, IgM anti-Ro was also significantly correlated to IgG anti-Ro among SLE patients, as well as to IgG anti-La and anti-dsDNA. We conclude that largely genetically determined, thus natural IgM anti-Ro-bearing precursor B-cells, may be an important factor for class switching and determinant spreading in early phases of SLE pathogenesis. Furthermore, we found unexpected sex differences in isotype/specificity correlations among SLE-unaffected relatives and control subjects, which could help understand the strong gender bias associated with SLE. We propose that the study of such correlation structures may reveal characteristic spreading pathways relevant for human SLE.

Alterations of self-reactive antibody repertoires in HIV disease: An insight into the role of T cells in the selection of autoreactive B cells

Infection with human immunodeficiency virus (HIV) is characterized by a progressive depletion of CD4(+) T cells that parallels a dysfunction of the B cell compartment and a disturbed recognition of self-antigens. The relationship between T lymphocyte homeostasis and abnormalities in the selection of self-reactive B cells is not clear as yet. We have therefore compared repertoires of natural antibodies of healthy donors and of patients at various stages of HIV infection. The reactivity of IgM and IgG antibodies in plasma of healthy blood donors and of HIV-positive patients with high and low CD4(+) T cell counts was assessed by semi-quantitative immunoblotting using self-antigens extracted from normal human tissues. Repertoires of reactivites were compared between groups of individuals by means of multiparametric statistical analysis. We observed that repertoires of self-reactive IgM and IgG from HIV-seropositive patients exhibited significantly altered patterns of reactivity, as compared to those of healthy controls. Further, self-reactive repertoires of IgM and IgG of patients with high CD4(+) T cell counts differed significantly from those of patients with low CD4(+) T cell counts. A longitudinal analysis of self-reactive antibody repertoires of progressor and non-progressor patients suggested an influence of CD4(+) T cell counts on immunoglobulin reactivity toward self-antigens. These observations support the hypothesis that altered T cell/B cell interactions due to altered CD4(+) T cell help severely impact on the selection of self-reactive antibody repertoires and may contribute to the onset of pathological autoimmunity in HIV disease.

Evolution of self-reactive IgG antibody repertoires in patients with relapsing-remitting multiple sclerosis

We have previously demonstrated a distortion of self-reactive IgG antibody repertoires in patients with multiple sclerosis (MS) compared to controls, by immunoblotting assays, using human brain homogenates. The analysis of the immune profiles against human brain antigens allowed us to distinguish MS patients, and to associate a particular pattern of reactivity for each clinical form of MS. The aim of the present study was to evaluate the evolution of such patterns in patients with relapsing-remitting MS (RRMS). In a first step, we confirmed, by western blotting using human brains as source of antigens, the existence of specific repertoires of IgG reactivity in whole serum collected from healthy subjects (n = 32) and from untreated patients with RRMS (n = 56). In a second step, the evaluation of patterns was performed at baseline and 1 year later in untreated RRMS patients (n = 15), and in RRMS patients treated with IFN-beta (n = 41). In both groups, little change in IgG reactivity in whole serum was found. However, a higher degree of stability was noted in treated versus untreated patients (P < 0.01). Our results have showed a specific and relatively stable pattern of reactivity for each RRMS individual tested against brain antigens even after a 1-year treatment prevailing in treated patients suggesting that IFN-beta could stabilize IgG antibody repertoires.

MAINTENANCE OF SERUM ANTIBODY LEVELS

In vertebrates, serum antibodies are an essential component of innate and adaptive immunity and immunological memory. They also can contribute significantly to immunopathology. Their composition is the result of tightly regulated differentiation of B lymphocytes into antibody-secreting plasma blasts and plasma cells. The survival of antibody-secreting cells determines their contribution to the immune response in which they were generated and to long-lasting immunity, as provided by stable serum antibody levels. Short-lived plasma blasts and/or plasma cells secrete antibodies for a reactive immune response. Short-lived plasma blasts can become long-lived plasma cells, probably by competition with preexisting plasma cells for occupation of a limited number of survival niches in the body, in a process not yet fully understood. Limitation of the number of long-lived plasma cells allows the immune system to maintain a stable humoral immunological memory over long periods, to react to new pathogenic challenges, and to adapt the humoral memory in response to these antigens.

Serum IgM, IgG and IgA block by F(ab')-dependent mechanism the binding of natural IgG autoantibodies from therapeutic immunoglobulin preparations to self-antigens

Natural polyreactive IgG autoantibodies are present in the plasma of healthy individuals and as a result in pooled therapeutic intravenous immunoglobulin (i.v.Ig) preparations. The spectrum of self-antigens to which these autoantibodies bind, their fate after intravenous infusion and their biological activity are not well understood. The identity of serum proteins that mask binding of natural autoantibodies to self-proteins is a matter of controversy. The spectrum of native serum proteins bound by i.v.Ig was analyzed by two-dimensional electrophoresis. The reactivity of i.v.Ig was directed mainly to circulating immunoglobulins. The binding of the IgG autoantibodies from i.v.Ig to native human liver antigens was blocked not only by a F(ab')2-dependent mechanism by circulating IgM and IgG (as has been previously suggested), but also by serum IgA. This control of anti-self reactivity may be inefficient in some autoimmune diseases.

Increased polyclonal immunoglobulin reactivity toward human and bacterial proteins is associated with clinical protection in human Plasmodium infection

Background

Polyclonal B-cell activation is well known to occur in Plasmodium infections, but its role in pathogenesis or protection remains unclear. However, protective properties of natural antibodies have previously been demonstrated in other contexts.

Methods

Sera from asymptomatic and symptomatic Plasmodium-infected subjects locally detected in a survey study in the Brazilian Amazon, and from unexposed and exposed but presently uninfected control subjects, were assayed by a standardized quantitative immunoblot method allowing simultaneous detection of IgG or IgM reactivity to a large number of parasite-unrelated proteins.

Results

In subjects free of coinfection with hepatitis B virus, IgG reactivity to human brain antigens and Escherichia coli proteins was strikingly enhanced in asymptomatic Plasmodium-infected individuals when compared to such with clinical malaria symptoms, or to uninfected control subjects. This difference was most characteristic for limited exposure times (less than ten years locally, or 20 years in endemic areas). It was more significant than a similar trend found for IgG to Plasmodium falciparum antigens, and unrelated to parasitaemia levels. Asymptomatic subjects with comparatively short exposure characteristically showed relatively elevated IgG versus IgM reactivity. Polyclonal IgG reactivity appears triggered by previous P. falciparum but not Plasmodium vivax malaria.

Conclusion

The observed difference in polyclonal antibody production seems related to intrinsic activation states of infected individuals, rather than to parasite-antigen specific immune responses. However, it appears influenced by preceding stimuli. This supports the idea that acquired clinical immunity may not exclusively depend on antigen-specific responses, but also on the individual polyclonal reaction.

Inherent specificities in natural antibodies: a key to immune defense against pathogen invasion

Natural antibodies are produced at tightly regulated levels in the complete absence of external antigenic stimulation. They provide immediate, early and broad protection against pathogens, making them a crucial non-redundant component of the humoral immune system. These antibodies are produced mainly, if not exclusively, by a subset of long-lived, self-replenishing B cells termed B-1 cells. We argue here that the unique developmental pattern of these B-1 cells, which rests on positive selection by self antigens, ensures production of natural antibodies expressing evolutionarily important specificities that are required for the initial defense against invading pathogens. Positive selection for reactivity with self antigens could also result in the production of detrimental anti-self antibodies. However, B-1 cells have evolved a unique response pattern that minimizes the risk of autoimmunity. Although these cells respond rapidly and strongly to host-derived innate signals, such as cytokines, and to pathogen-encoded signals, such as lipopolysaccharide and phosphorylcholine, they respond very poorly to receptor-mediated activation. In addition, they rarely enter germinal centers and undergo affinity maturation. Thus, their potential for producing high-affinity antibodies with harmful anti-self specificity is highly restricted. The positive selection of B-1 cells occurs during the neonatal period, during which the long-lived self-renewing B-1 population is constituted. Many of these cells (B-1a) express CD5, although a smaller subset (B-1b) does not express this surface marker. Importantly, B-1a cells should not be confused with short-lived anergic B-2 cells, which originate in the bone marrow in adults and initiate CD5 expression and programmed cell death following self-antigen recognition. In summary, we argue here that the mechanisms that enable natural antibody production by B-1 cells reflect the humoral immune system, which has evolved in layers whose distinct developmental mechanisms generate complementary repertoires that collectively operate to maximize flexibility in responses to invading pathogens. B-2 cells, present in what may be the most highly evolved layer(s), express a repertoire that is explicitly selected against self recognition and directed towards the generation of high-affinity antibody response to external antigenic stimuli. B-1 cells, whose repertoire is selected by recognition of self antigen, belong to what may be earlier layer(s) and inherently maintain production of evolutionarily important antibody specificities that respond to pathogen-related, rather then antigen-specific signals.

The natural autoantibody repertoire and autoimmune disease

The incidence of autoimmune diseases has shown a significant increase in developed countries during the last 40 years. The cause of this increase is still unknown, and reliable methods for the detection of individuals at risk of developing autoimmune disease are not available yet. To explore new methods for the diagnosis and monitoring of autoimmune disease, we have studied the repertoire of natural autoantibodies (NA) and its relationship with autoimmune disease using large arrays of defined antigens. NA are found in healthy humans and mice, apparently in the absence of immunization with their target antigens. We used knock-out mice to demonstrate that the repertoire of NA is influenced by factors not directly related to antigenic stimulation such as endogenous levels of histamine. By studying strains of mice known to differ in their susceptibility to autoimmune disease, we could conclude that the repertoire of NA reflects the susceptibility to develop autoimmune disease. The study of the human repertoire of NA required the development of bio-informatic tools to overcome the variation introduced by individual differences in the genetic background and immune history. We found that human NA are organized in clusters that can differentiate healthy subjects from patients with type 1 diabetes mellitus, type 2 diabetes mellitus or Behçet's disease patients. The development of new tools to undertake large-scale NA analysis could also enhance our understanding of the immune system, and leave us in a better position to face the up-coming epidemics of autoimmune disorders.

Autoantibody repertoires to brain tissue in autism nuclear families

The hypothesis of an immune dysfunction in autism spectrum disorders has previously been put forward without, however, compelling evidence of a direct relation to its etiology or pathogenesis. To further understand if autoimmunity could play a significant role in autism, we analyzed autoantibody repertoires to brain tissue extract in the plasma of 171 autism children, their parents, and 54 controls, by quantitative immunoblotting. Multiparametric analysis revealed significant differences between patients and controls, and showed that one single reactivity in Section 32 of the blot had the most power to discriminate between these samples. Family correlation coefficients and heritability estimates did not provide any evidence that this reactivity was genetically determined. While the molecular weight of the target protein suggested that it might be an isoform of Myelin Basic Protein (MBP), inhibition assays with human MBP argued against this hypothesis. The study evidences the widespread occurrence of autoreactivities to brain tissue in autism patients, which may represent the immune system's neuroprotective response to a previous brain injury occurred during neurodevelopment. The molecular identification of the target protein in Section 32 will contribute to the understanding of the role of immune responses against brain antigens in autistic patients.

Immunological aspects of heat-shock proteins-the optimum stress of life

This review summarizes the complex role of heat-shock proteins (Hsp) in immune reactions, especially the cellular effects of heat-shock proteins during the recognition processes by innate immunity. The role of heat-shock proteins in the pathogenesis of two multifactorial diseases, i.e. inflammatory bowel disease (IBD) and atherosclerosis is highlighted. A new hypothesis on "immunodeficiency burden" is presented. According to this hypothesis, susceptibility to any multifactorial disease in any given subject and in the presence of specific environmental factors is the aggregate effect of polymorphisms resulting in the failure of protective immunity with consequent disease.

IgG reactivity with a 100-kDa tissue and endothelial cell antigen identified as topoisomerase 1 distinguishes between limited and diffuse systemic sclerosis patients

We have analyzed antibody (Ab) reactivities of patients with limited systemic sclerosis (SSc) and anti-centromere Ab, patients with diffuse SSc and anti-topoisomerase 1 (anti-topo 1) Ab, patients with diffuse SSc without anti-topo 1 or anti-centromere Ab and age- and gender-matched healthy controls with normal human tissue and endothelial cell (EC) antigens. IgG reactivities with tissue antigens differed significantly between patients with anti-topo 1 Ab and patients with anti-centromere Ab. One 100-kDa band identified as topoisomerase 1 in macrovascular and microvascular EC extracts was recognized by IgG from patients with anti-topo 1 Ab and 50% of patients without specific Ab. IgG from patients with limited SSc and anti-centromere Ab, but not those of other patients or controls specifically recognized a 80-kDa band only in microvascular EC. Our results indicate that Ab from patients with limited or diffuse SSc with or without anti-topo 1 Ab exhibit specific and mutually exclusive reactivity patterns.

Changes in pools of autoantibodies and anti-bacterial antibodies in patients suffering from recurrent infections of the urinary tract and undergoing bacterial immunization treatment

Antibodies (Abs) (IgM, IgA, IgG and IgG subclasses) specific for several uropathogenic strains (Escherichia coli, Pseudomonas sp. and Klebsiella sp.) as well as anti-phospholipids, anti-beta2-glycoprotein I and anti-laminin antibodies were analyzed in the sera of 20 patients with long-lasting uncomplicated recurrent infections of the lower urinary tract who underwent immunization treatment with a mixture of heat-inactivated bacteria. Immunization had a dual effect: a marked prolongation of the infection-free period in more than half of tested patients (which could be related to the profiles of anti-bacterial antibodies), and the induction of a significant decrease in autoreactivity. The results obtained showed that prolonged infections resulted in a significant rise in IgG specific for phospholipids, beta2-glycoprotein I and mouse laminin. However, irrespective of the effect on urinary tract infection per se, immunization induced a noticeable decrease in reactivity toward those antigens (Ag). The most abundant autoantibodies prior to immunization treatment were of IgG2 subclass. A statistically significant decrease in phospholipid specific antibodies belonging to this subclass, and in the concentration of Y7 cross-reactive idiotope, registered only in the responder group; this indicates the significance of natural antibody pool involvement in a proper anti-bacterial immune response.

Knock-out of the histidine decarboxylase gene modifies the repertoire of natural autoantibodies

Natural antibodies (NA) are antibodies produced in the absence of known immunization with specific antigens. NA are found in the blood of healthy humans and mice. Histamine influences many aspects of the immune response, including antibody production. However, the role of histamine in the generation of NA has not yet been studied. In this work, we used an ELISA assay to characterize the self-antigen binding repertoires of NA in wild type (WT) mice and in histidine decarboxylase knock-out (HDC-KO) mice, unable to synthesize histamine. We now report that HDC-KO and WT mice differed in the patterns of autoreactivity of their IgM and IgG NA. The NA in HDC-KO sera manifested a larger repertoire of IgM autoantibodies than did the WT sera. The self-antigens bound by IgM from HDC-KO mice included structural proteins, enzymes associated with cellular metabolism, double-stranded and single-stranded DNA, and tissue-specific antigens like insulin. There were relatively fewer differences in the NA repertoire of IgG autoantibodies of the mice: notably, the HDC-KO sera reacted with glutamic acid decarboxylase (GAD), an antigen associated with autoimmune diabetes. These results demonstrate that endogenous histamine can influence the self-reactivity of the NA repertoire.

Distortion of the Self-Reactive IgG Antibody Repertoire in Multiple Sclerosis as a New Diagnostic Tool

To date, none of the myelin-associated Ag targets definitively discriminates between the immune response observed in multiple sclerosis (MS) patients and healthy subjects. However, it has been shown recently that analysis of global immune Ab profiles such as natural autoantibody reactivities can help to distinguish between normal individuals and patients suffering from various immune diseases. The aim of our study was to compare the global IgG immune response against brain self-Ags in sera from 82 MS patients and 27 healthy subjects. The analysis of the immune profiles was performed by Western blotting, and data were subjected to linear discriminant analysis. Particular patterns of IgG reactivity were found in healthy subjects, Sjögren patients, and MS patients. Moreover, this approach separated the three clinical forms of MS with a high concordance rate with the clinical data (kappa value, 77.8%). Our study suggests, for the first time, that serum IgG Ab repertoires are able to distinguish MS patients. In addition, our data suggest that patterns of IgG reactivity could model the pathological processes underlying the various forms of MS. Further characterization of such discriminant Ags could provide useful information regarding their potent role in pathogenesis or regulatory processes in MS.

IgM and IgG autoantibodies from microscopic polyangiitis patients but not those with other small- and medium-sized vessel vasculitides recognize multiple endothelial cell antigens

Using a quantitative immunoblotting technique on extracts of macrovascular and microvascular endothelial cells (EC), we analyzed serum IgM and IgG reactivities of patients with active disease fulfilling the ACR and Chapel Hill criteria for the diagnosis of polyarteritis nodosa (PAN) (n = 8), PAN related to hepatitis B virus (HBV) infection (HBV-PAN) (n = 5), Wegener's granulomatosis (n = 6), microscopic polyangiitis (MPA) (n = 18), Churg-Strauss syndrome (n = 8), and patients with chronic HBV infection without PAN (n = 5) and age- and gender-matched healthy individuals (n = 45). MPA patients' IgM bound to 200-, 105-, 80-, 65-, 45-, 35-, and 33-kDa major bands, whereas IgM from controls and other patients bound predominantly to the 65-kDa band in EC extracts. MPA patients' IgG reacted mainly with 105-, 70-, 55-, and 38-kDa protein bands, whereas IgG from controls and other patients did not. Our results provide evidence that IgM and to a lesser degree IgG from MPA patients specifically recognize multiple EC antigens.

Autoreactive antibody repertoire is perturbed in atherosclerotic patients

In patients with clinical symptoms of coronary atherosclerosis, T cells are activated and directed to autologous proteins contained in the active plaques, suggesting that autoimmune responses may play a role in atherosclerosis progression. Organ-specific autoimmune diseases are sometimes accompanied by broad alterations of serum autoreactive antibody repertoires. We thus investigated antibody repertoires at a global level, using a technique of immunoblotting that allows for the quantitative screening of antibody reactivities in complex antibody mixtures toward a large panel of antigens derived from homologous tissue extracts, followed by multiparametric statistical analysis of the data. We analyzed the autoreactive IgG repertoire in 20 patients with documented coronary atherosclerosis and in 20 matched healthy controls. Total proteins from atherosclerotic carotid specimens and normal arterial tissues (target organs) and from kidney, liver, and stomach (non-target control organs) were used as panels of antigens. Patients had a significantly perturbed antibody repertoire and an enhanced autoreactivity of IgG to target and non-target organs, as compared with controls. Reactivity of purified IgG to plaque and normal artery proteins was greater in patients, but reactivity of IgG in the whole serum toward normal arterial tissue was lower than in controls; this suggests that, in patients, autoreactivity toward normal arteries is regulated by serum factors. Our data indicate that atherosclerotic patients develop a perturbed humoral immune response directed toward arterial proteins, which impacts on the overall autoreactive repertoire. These findings further substantiate that autoimmune processes take place in atherosclerosis and most likely influence disease progression.

Titration of serum anti-ganglioside antibodies in patients with chronic medular injury previous to treatment with GM1 ganglioside

Anti-ganglioside serum titers were evaluated by ELISA in 150 patients with complete spinal cord lesion for 6 to 12 months (IgG monosialo GM1, IgM monosialo GM1, IgG asialo GM1, IgM asialo GM1, IgG disialo GD1b e IgM disialo GD1b) prior to treatment with GM1 100 mg/day i.m. Only 4 patients showed positive titers for anti-asialo-GM1 (IgM) antibodies . All patients were clinically examined during and after treatment. No important side effects were observed with GM1 therapy. These results suggest that GM1-ganglioside administration in patients with chronic spinal cord injury is safe.

Molecular aspects of allergy

Atopic diseases such as asthma, rhinitis, eczema and food allergies have increased in most industrialised countries of the world during the last 20 years. The reasons for this increase are not known and different hypotheses have been assessed including increased exposure to sensitising allergens or decreased stimulation of the immune system during critical periods of development. In allergic diseases there is a polarisation of the Th2 response and an increase in the production of type 2 cytokines which are involved in the production of immunoglobulin E and the development of mast cells, basophils and eosinophils leading to inflammation and disease. The effector phase of atopy is initiated by interaction with Fc epsilon RI expressed on effector cells such as mast cells and basophils but also found on an ever increasing list of cells. Binding of a polyvalent allergen to the variable part of IgE leads to a cross-link of the receptor that triggers the cell to release histamine and pharmacological mediators of the symptomatic allergic response. Cross-linking of Fc epsilon RI by autoantibodies against the alpha-chain of the Fc epsilon RI, causing subsequent histamine release is thought to be involved in the pathogenesis of other diseases such as chronic idiopathic urticaria (CIU). To date, most therapeutic strategies are aimed at inhibiting and controlling components of the inflammatory response. Recently, new treatment strategies have emerged that focus on the development of preventive and even curative treatments. The most promising therapeutic approaches are aimed at inhibiting the IgE-Fc epsilon RI interaction with the use of non-anaphylactogenic anti-IgE or anti-Fc epsilon RIalpha autoantibodies. Clinical trials in humans using an humanised anti-IgE antibody showed that this antibody was well tolerated and reduced both symptoms and use of medication in asthma and allergic rhinitis. Thus interruption of the atopic cascade at the level of the IgE-Fc epsilon RI interaction with the use of non-anaphylactogenic antibodies is effective and represents an attractive therapy for the treatment of atopic disease.

B cell positive selection by soluble self-antigen

It is well established that autoreactive B cells undergo negative selection. This stands in paradox with the high frequency of so-called natural autoreactive B cells producing low affinity polyreactive autoantibodies with recurrent specificities, suggesting that these B cells are selected on the basis of their autoreactivity. We previously described two transgenic mouse lines (with and without IgD) producing a human natural autoantibody (nAAb) that binds ssDNA and human Fcgamma. In the absence of human IgG, nAAb-transgenic B cells develop normally. By crossing these mice with animals expressing knockin chimeric IgG with the human Fcgamma, we now show that the constitutive expression of chimeric IgG promotes the increase of nAAb-expressing B cells. This positive selection is critically dependent on the presence of IgD, occurs in the spleen, and concerns all mature B cell subsets, with a relative preferential enrichment of marginal zone B cells. These data support the view that soluble self-Ags can result in positive clonal selection.

Red blood cell transfusions are associated with alterations in self-reactive antibody repertoires of plasma IgM and IgG, independent of the presence of a specific immune response toward RBC antigens

Immunization to allogeneic RBC antigens occurs in transfused patients, and may be associated with the development of RBC-destructive antibodies directed against autologous RBC. The present study investigates the effect of transfusion of allogeneic RBC on self-reactive antibody repertoires, independent of the presence of a specific immune response directed toward RBC antigens. Antibody repertoires of IgM and IgG in plasma of hematological patients prior to starting a transfusion regime and of hematological patients receiving regular transfusions of leukocyte-depleted RBC were analyzed using quantitative immunoblotting on a panel of antigens derived from tissue and cell extracts, followed by multiparametric statistical treatment of the data. Multiparametric statistical analysis discriminated between self-reactive antibody repertoires of patients prior to starting a transfusion regime and those receiving regular RBC transfusions (IgM, 0.0001 < P < 0.0244/IgG, 0.0002 < P < 0.0088, depending on the tissue extract), whereas antibody repertoires of plasma IgM and IgG toward bacterial antigens were similar between groups of patients (P > 0.05). We conclude that the challenge of the immune system with allogeneic RBC antigens influences self-reactive antibody repertoires of plasma IgM and IgG, independent of the presence of a specific immune response toward RBC antigens.

Regeneration of natural antibody repertoire after massive ablation of lymphoid system: robust selection mechanisms preserve antigen binding specificities

Natural Abs (NAbs) are Igs present in the serum and body fluids of healthy vertebrate animals, without any previous intentional immunization. NAbs often exhibit autoreactivity but also play an essential role in immunity, being a first line of defense against infectious microorganisms. We have previously analyzed the natural serum IgM Ab repertoire of normal mice, characterizing their reactivity with hundreds/thousands of self Ags; a significant similarity among different individuals was observed, and it was found that many reactivities of NAbs stably kept during adulthood were established early in life, implicating that period as a critical time window in the physiology of NAb repertoire selection. In the work reported here, experiments were conducted to address the role of normal lymphocyte ontogeny to the formation and stability of adult NAb repertoire. The massive destruction of the lymphoid system was promoted in adult mice with gamma-irradiation, and regeneration of hemopoietic tissues was granted by bone marrow or fetal liver inoculum. NAb repertoire regeneration was followed for 60 days after gamma-irradiation in bone marrow or fetal liver chimeric animals. The analysis of serum IgM reactivity with hundreds/thousands of self Ags showed that the NAb repertoire regenerated most of its original format after massive destruction of lymphoid compartments, characterizing autoreactive repertoire selection as a robust biological process. The data also show that regeneration of the NAb repertoire occurred similarly in fetal liver and bone marrow chimeras, although the latter animals poorly reconstituted their CD5(+) B1 cell compartment, suggesting that B1 cells are not essential for natural Ab regeneration.

Long-term kinetics of adult human antibody repertoires

In healthy humans, antibody repertoires change during ontogeny and senescence. The dynamics of antibody repertoires among adults over a longer period of time in one and the same individual has, however, not been extensively studied. In this study we analysed peripheral blood samples from five healthy adults, taken over a period of 10 weeks and once 9 years later. A competitive, quantitative polymerase chain reaction (PCR) was developed to investigate short and long-term variations in VH gene family repertoires. Serum antibody levels to common self and non-self antigens were determined in samples taken at the same time-points as the cell samples to analyse possible correlations between molecular and serological expression profiles. We found a high degree of stability in the VH gene family repertoire over time as well as between individuals with a Caucasian background. A specific change in the usage of primarily the VH3 and VH5 gene families was observed in one individual at one time-point. The deviating pattern resembled the VH gene family utilization pattern observed in naturally activated B lymphocytes. The fluctuations in VH3 and VH5 gene family expression correlated with the presence of rheumatoid factor in serum. We discuss the possible influence of polyclonal, transient stimulation of B cells on VH gene repertoires, as measured in circulating B cells.

Autoantibodies to heat shock protein 90 in the human natural antibody repertoire

The present study demonstrates the presence of natural autoantibodies of the IgG isotype directed against heat shock protein 90 (HSP90). The binding properties of affinity-purified anti-HSP antibodies were compared with those of natural antibodies specific for other self antigens, including anti-thyroglobulin and anti-myoglobin autoantibodies, by using semiquantitative immunoblotting, with solubilized proteins from normal liver tissue as antigens, and cross-blot analysis using purified self proteins. Affinity-purified anti-HSP90 antibodies were polyreactive and the non-HSP90-specific fraction of normal IgG was depleted in its natural autoantibody content. We further observed that self antigens including HSP, myosin, tubulin and aldolase with highly conserved structures show similar patterns of binding with natural antibodies, and form a well-defined cluster as demonstrated by cluster analysis of immunoreactivity data, whereas the less-conserved self and non-self antigens remained unclustered. The results favor the hypothesis that HSP90 belongs to a subset of highly conserved and immunodominant self antigens that are the primary target for natural autoantibodies in normal human IgG.

Idiopathic membranous glomerulonephritis is associated with altered patterns of self-reactive IgM and IgG antibody repertoires

Idiopathic membranous glomerulonephritis (MGN) is an immune complex nephropathy characterized by the subepithelial deposition of immunoglobulin (Ig)G. The pathogenesis of the disease remains largely unknown, but recent evidence suggests that human MGN may involve an autoimmune component. In the present study, we have analyzed the IgM and IgG antibody repertoires of patients with MGN towards self- and nonself-antigens using a technique of quantitative immunoblotting on a panel of whole human tissue or solubilized bacterial cell extracts as sources of antigens. Data were compared by means of multiparametric statistical analysis. We demonstrate that the antibody repertoires of self-reactive IgM and IgG in plasma of patients with MGN exhibit significantly altered patterns of reactivity, as compared with those of healthy controls. In contrast, multiparametric statistical analysis does not discriminate the reactivity patterns of IgM and IgG in plasma of patients and healthy controls towards nonself antigens. These observations indicate that a failure in the regulation of physiological self-reactivity is associated with immune complex nephropathy in MGN.

Autoantibody patterns in diabetes-prone NOD mice and in standard C57BL/6 mice

Autoantibodies are commonly found in healthy individuals and strains of mice that are not prone to autoimmunity. The present study was undertaken to identify self antigens recognized by serum autoantibodies from unimmunized mice of two strains: NOD mice prone to spontaneously develop autoimmune diabetes and C57BL/6 mice known to be relatively resistant to autoimmune disease. IgM and IgG autoantibodies detected in the sera of NOD and C57BL/6 mice manifested different patterns of reactivity. The IgM autoantibodies from C57BL/6 serum reacted with more self antigens and showed higher OD values than the IgM autoantibodies from NOD mice. In contrast, the IgG autoantibodies from NOD serum reacted with more antigens and displayed higher OD readings than did IgG autoantibodies from C57BL/6 mice. Among the antigens recognized by the autoantibodies, particularly of the IgG class, were self antigens known to induce experimental autoimmune diseases in NOD and C57BL/6 mice. In addition, IgG autoantibodies from NOD mice reacted with self antigens reported to mark the spontaneous autoimmune diabetes that characterizes this strain of mice. These results suggest that naturally occurring IgG autoantibodies reflect susceptibility to induction of specific autoimmune diseases. In addition, the results suggest that IgM autoantibodies may by associated with mechanisms that might prevent autoimmune disease.

Striatal antibodies in children with Tourette's syndrome: multivariate discriminant analysis of IgG repertoires

Antineuronal antibodies have been postulated to be the underlying pathophysiology in TS and other neuropsychiatric disorders. Serum antibodies from 20 children with TS, and 21 control subjects against human striatum, globus pallidus, muscle, and HTB-10 cells were assayed by Western blot techniques. A MANOVA differentiated between TS and control blots, and a discriminant analysis demonstrated which variables contributed most to differences between groups. Prominent differences between TS and control blots were identified using striatal epitopes in contrast to similar patterns shown between groups for globus pallidus, muscle and HTB-10 tissue, supporting striatal autoimmune involvement in TS pathophysiology.

Different dysregulations of the natural antibody repertoire in treated and untreated HIV-1 patients

To investigate a possible dysregulation of the autoantibody network in AIDS patients, the relative activity of representative natural antibodies was measured in serum IgG and IgM. These immunoglobulins were purified from two cohorts of 20 HIV-infected patients undergoing, or not, a triple combination therapy. A cohort of 20 normal patients was used as a control. Marked alterations of the natural antibody repertoire were observed, varying according to the isotype and specificity of the antibody studied. For the classical self-protein antigens, human actin and myosin, the changes observed in the untreated cohort were absent in the treated cohort. In contrast, no changes, or even increased changes of the activity of antibodies to special antigens, DNA and TNP, occurred in the treated cohort. The differences were highly significant, indicating that this repertoire is regulated and not randomly modified by the disease. These results suggest the presence of different factors of dysregulation of the B cell repertoire of natural antibodies associated with the disease as well as with the treatment. These major dysregulations may favor the autoimmune phenomena observed during HIV infection.

Broad alterations of self-reactive antibody-repertoires of plasma IgM and IgG in B-cell chronic lymphocytic leukemia (B-CLL) and B-CLL related target-restricted autoimmunity

B-cell chronic lymphocytic leukemia (B-CLL) is characterized by a malignant CD5+ B-cell clone. The leukemic clone commonly expresses IgM antibodies exhibiting reactivity toward a wide range of self-antigens. However, B-CLL associated autoimmunity is typically restricted to self-antigens expressed by blood cells, and mediated by IgG autoantibodies of polyclonal origin. In the present study, we addressed the question whether self-reactive antibody repertoires of plasma IgM and IgG are disturbed by monoclonal immunoglobulins of B-CLL patients, and whether antibody repertoires of patients exhibiting B-CLL associated target-restricted autoimmune disease (AID) differ from those of B-CLL patients without AID. We investigated antibody repertoires at a global level, using a technique of quantitative immunoblotting that allows for the quantitative screening of antibody reactivities in complex antibody mixtures toward a large panel of antigens derived from homologous tissue extracts, followed by multiparametric statistical analysis of the data. We demonstrate that self-reactive antibody repertoires of plasma IgM and IgG are broadly altered in patients with B-CLL, that alterations in self-reactive antibody repertoires are not restricted to B-CLL patients exhibiting AID, and that target-restricted autoimmunity in B-CLL patients is associated with altered antibody repertoires not restricted to the target organ. We conclude that monoclonal alterations of immunoglobulin production in B-CLL are associated with broad defects of self-reactive antibody repertoires. Our observations suggest that the application of therapeutic IVIg preparations might influence B-CLL by restoring normal self-reactive antibody repertoires in plasma.

Effect of human immunoglobulins on the immunogenicity of porcine bioprostheses

BACKGROUND

Glutaraldehyde fixation (GT) is known to reduce immunologic reactions and tissue degeneration after implantation in humans. Sterilization after glutaraldehyde fixation (G-ST) improves the safety and reduces the tendency of GT valves to calcify. Intravenous immunoglobulins (IVIg) have been shown to reduce xenogeneic response against porcine tissue. We have investigated the effect of these fixation procedures combined with and without IVIg on the antigenicity of bioprostheses.

METHODS

Lewis adult rats were implanted subcutaneously with a fresh, GT, or G-ST porcine heart valve pre- or posttreated with different amounts of IVIg. We followed by enzyme-linked immunosorbent assay and IgM and IgG titers against protein extracts from the porcine heart valves after implantation. Cellular reactivity was assessed in xenogeneic lymphoendothelial coculture experiments. Calcification content was also examined.

RESULTS

Glutaraldehyde fixation partially decreased the humoral response against proteins of the implant but elicited a cellular xenogeneic response. Sterilization reduced these reactivities, but retained antigenicity. Intravenous immunoglobulin postincubated with GT valves before implantation reduced the antigenicity of the tissue to the same extent as G-ST valves, but had no effect on valvular tissue calcification.

CONCLUSIONS

Our studies demonstrate that IVIg or the sterilization procedure (ST) reduced the cellular response against glutaraldehyde-fixed valves (GT), whereas reduced calcification was observed only with ST.

Altered antibody repertoires of plasma IgM and IgG toward nonself antigens in patients with warm autoimmune hemolytic anemia

Warm autoimmune hemolytic anemia (WAIHA) is characterized by an accelerated extravascular clearance of red blood cells (RBC) mediated by RBC-bound IgG autoantibodies. We have recently demonstrated significantly altered self-reactive antibody (Ab) repertoires of plasma IgM in WAIHA patients. The natural IgM Ab repertoire in plasma is critical in modulating both autoimmune and alloimmune responses. In the present study, we investigated IgM and IgG Ab repertoires of WAIHA patients toward nonself antigens (Ag) using a quantitative immunoblotting technique, followed by multiparametric statistical analysis of the data. We demonstrate significantly altered Ab repertoires of IgM and IgG toward nonself Ag in WAIHA patients. The reactivity of plasma IgM of WAIHA patients was reduced compared to that of healthy individuals, independent of administering an immunosuppressive therapy. We observed that an increase in reactivity of plasma IgM during clinical remission of the disease was associated with the development of allo-Ab toward RBC-antigens during RBC transfusions. Taken together, the data indicate altered Ab repertoires of plasma IgM and IgG toward nonself Ag in WAIHA patients. A broadly reduced reactivity of plasma IgM toward nonself Ag might influence the adaptive immune response in WAIHA patients.

Comparative study on antibodies to human and bacterial 60 kDa heat shock proteins in a large cohort of patients with coronary heart disease and healthy subjects

BACKGROUND

Recent observations indicate an association between antibodies against mycobacterial heat shock protein (hsp65) and coronary heart disease (CHD). Previously, we reported on marked differences in antigen specificity and complement activating ability of anti-hsp65 antibodies and auto-antibodies against human heat shock protein, hsp60. Here, we investigated whether there are differences between antih-sp65 and anti-hsp60 antibodies in their association with CHD.

DESIGN

We measured by ELISA the levels of antibodies to hsp65, hsp60 and E. coli-derived GroEL in three groups: Group I, 357 patients with severe CHD who underwent by-pass surgery; Group II, 67 patients with negative coronary angiography; Group III, 321 healthy blood donors. Antibodies against Helicobacter pylori were also measured by commercial ELISA.

RESULTS

As calculated by multiple regression analysis, the levels of anti-hsp60 auto-antibodies were significantly higher in Group I compared to Group II (P = 0.007) or Group III (P < 0.0001). By contrast, although concentrations of anti-hsp65 and anti-GroEL antibodies in Group I were higher than in Group III, no significant differences between Group I and Group II were found. Antibodies to the two bacterial hsp strongly correlated to each other, but either did not correlate or weakly correlated to hsp60. In Group I, serum concentrations of anti-H.pylori antibodies significantly correlated with those of anti-hsp65 and anti-GroEL antibodies but they did not correlate with the anti-hsp60 antibodies.

CONCLUSIONS

As to their clinical relevance, a remarkable difference become evident between antibodies to human hsp60 and antibodies against bacterial hsp in the extent of association with CHD. On the basis of these findings and some pertinent literature data, an alternative explanation for the association between high level of anti-hsp antibodies and atherosclerotic vascular diseases is raised.

Induction of natural autoantibody activity following treatment of human immunoglobulin with dissociating agents

Treatment of normal polyclonal human IgG and of F(ab')2 fragments of IgG with 6.0 M urea, 1.3 M sodium thiocyanate or with acidic buffers (pH 2.0), resulted in a dramatic and selective enhancement of the preexisting antibody reactivity with self antigens. Enhanced antibody activity revealed by the dissociating agents was inhibited by the addition of an excess of the relevant soluble antigen. Human monoclonal IgG, including four different IgG1m(1) V(H)3+ and V(K)3+ paraproteins differing only in their CDRs, exhibited different changes in reactivity following urea treatment indicating major involvement of CDR sequences. The calculated dissociation constant of the binding reaction of normal IgG to the self antigen actin was 10(-6) M, whether IgG had been treated or not, indicating that the treatment increased the proportion of available self-reactive molecules instead of increasing the affinity of the preexisting natural autoantibodies. Enhanced autoreactivity was not due to aggregation of Ig, unmasking of the antibody site by removal of low MW antigens, nor to the denaturation of natural Id-anti-Id complexes. Taken together, these results suggest that treatment of Ig with dissociating agent results in the exposure of basic polyreactive antibody structures. The enhancement of reactivity may be of relevance in physiology of mucosal immunity and in therapeutic immunomodulation.

Altered self-reactive antibody repertoires are a general feature of patients with myelodysplastic syndrome

Myelodysplastic syndrome (MDS) is characterized by an acquired clonal disorder of haematopoietic progenitor cells that results in inhibition of normal haematopoiesis and contributes to the development of haematological malignancies. Autoimmune syndromes may occur in MDS, but they are not a major clinical feature of the disease. In the present study, we have analysed the global antibody repertoires of IgM and IgG in plasma of 10 patients with MDS toward self- and non-self-antigens by quantitative immunoblotting. Myelodysplastic syndrome patients included in this study did not exhibit autoimmune symptoms nor secondary haematological neoplastic disease. Data were compared by means of multiparametric statistical analysis. We demonstrate that the antibody repertoires of self-reactive IgM and IgG of patients with MDS exhibit significantly altered patterns of reactivity, as compared to those of healthy individuals. In contrast, reactivity patterns of IgM in plasma of patients and of healthy controls toward non-self-antigens were similar, whereas reactivity patterns of IgG of patients and healthy subjects toward non-self-antigens were discriminated by multiparametric statistical analysis. These observations indicate that a broad disturbance of self-recognition mechanisms is a general feature of patients with MDS. A failure in the regulation of self-reactivity may contribute to the pathogenesis of MDS.

Significant association between the skewed natural antibody repertoire of Xid mice and resistance to Trypanosoma cruzi infection

The Xid mutation predominantly affects the development of B cells and consequently the levels and composition of natural antibodies in sera. In contrast to the congenic and susceptible BALB/c strain, immunodeficient BALB.Xid mice display a resistant phenotype both to acute Trypanosoma cruzi infection and to the development of severe cardiopathy. Because natural antibodies are known to be basically self-antigen driven, IgM and IgG natural antibody repertoires (NAR) were compared before and during infection in these two strains. The analysis revealed fundamental alterations of IgM and IgG NAR in pre- and post-infected Xid mice. In particular, relatively increased natural (pre-existing) autoreactive IgG, dominated by the unique recognition of a single band in autologous heart extracts, was typical for uninfected Xid mice. This natural autoreactive IgG directed to heart antigens disappeared early after infection not only in Xid, but also in individual BALB/c mice that survived the acute infection. Conversely, the subgroup of BALB/c mice that died early after infection presented the most pronounced instances of the rapid, relative increase of IgM reactivities to self and non-self proteins. These results suggest that self-reactive NAR may play a role in an immunoregulatory mechanism relevant for the determination of susceptibility/resistance to infections. This may act either by influencing specific responses, or by modulating the self-aggressive components responsible for pathology.

Reconstitution of self-reactive antibody repertoires of autologous plasma IgM in patients with non-Hodgkin's lymphoma following myeloablative therapy

In healthy individuals, natural self-reactive antibody repertoires are restricted to a limited subset of autoantigens that is selected early in development and that remains invariant between individuals through aging. In the present study, we addressed the question of whether self-reactive antibody repertoires of plasma IgM change during high-dose chemotherapy (HDCT) with autologous blood stem cell support and whether antibody repertoires generated during immune reconstitution are similar to those present under physiological conditions. We followed the development of antibody repertoires in patients undergoing HDCT for the treatment of B-cell non-Hodgkin's lymphoma (NHL). Antibody repertoires were investigated by quantitative immunoblotting on whole tissue extracts as sources of self-antigens and by multiparametric statistical analysis of the data. We demonstrate that self-reactive antibody repertoires of plasma IgM of NHL patients prior to HDCT differ from those of healthy individuals, that they change during recovery of immune functions, and that antibody repertoires similar to those of healthy individuals are generated during immune reconstitution. We conclude that the mechanisms responsible for the selection of self-reactive repertoires of autologous plasma IgM during immune reconstitution after HDCT may follow those present under physiological conditions and that immune reconstitution may include a shift from altered toward normal patterns of self-reactivity.

Polyreactivity of disease-associated anti-RBC IgG autoantibodies of patients with warm autoimmune haemolytic anaemia and natural anti-RBC IgG autoantibodies of healthy individuals

Anti-red blood cell (RBC) immunoglobulin G (IgG) autoantibodies are present in patients with warm autoimmune haemolytic anaemia (WAIHA), and, as natural autoantibodies, in healthy individuals. This study investigated whether the feature of polyreactivity discriminates disease-associated from natural anti-RBC IgG autoantibodies. The patterns of reactivity of purified anti-RBC IgG eluted from the RBC of WAIHA patients and from the RBC of healthy individuals were analysed using quantitative immunoblotting on a panel of whole human tissue or bacterial cell extracts as antigen sources. In parallel, the reactivity patterns of IgG purified from plasma were analysed. Anti-RBC IgG of WAIHA patients and of healthy individuals recognized a wide range of self- and nonself-antigens. The reactivity patterns of anti-RBC IgG were homogeneous among patients and controls, did not differ between patients and controls, and were similar to those of IgG purified from plasma in the case of both patients and healthy individuals. The data demonstrate that the anti-RBC IgG autoantibodies of WAIHA patients share extensive similarity with those of healthy individuals. Polyreactivity is a common feature of both disease-associated and natural anti-RBC IgG autoantibodies.

Analysis of human self-reactive antibody repertoires by quantitative immunoblotting

We review the use of a quantitative immunoblotting technique to characterize human self-reactive antibody repertoires in health and disease. The interactions of plasma IgM and IgG with tissue extracts as sources of self-antigens were analyzed by quantitative immunoblotting. Data were compared by means of multiparametric statistical analysis. The data summarized here demonstrate that natural self-reactive antibody repertoires of healthy individuals are restricted to a limited subset of immunodominant autoantigens that is selected early in development, and remains conserved between individuals through ageing. The selection of human natural self-reactive IgG antibody repertoires requires normal T-/B-cell interactions. The immunoblotting assay has the potential to distinguish between autoimmune diseases with organ-related oligoclonal expansion of self-reactive clones and those characterized by broad alterations of immunoregulation. However, organ-specific autoimmune diseases may be characterized by altered patterns of antibody repertoires unrelated to the target organ. The assay also revealed an unexpected defect in the regulatory function of self-reactive IgM on the expression of self-reactive IgG repertoires in several systemic and organ-specific autoimmune diseases. The results are discussed in the light of our current understanding of the processes of selection of self-reactive B-cells and the pathophysiology of autoimmunity.