Spontaneous IgM autoantibody production in vitro by B lymphocytes of normal human neonates

Advances in Pretransplant Donor-Specific Antibody Testing in Solid Organ Transplantation: From Bench to Bedside

Immunological risk stratification has a central role in determining both the feasibility of solid organ transplantation and the type (and amount) of induction and maintenance immunosuppressive therapy. Currently there is poor consensus on how to exactly estimate the global immunological risk, and most transplant centers adopt complicated internal guidelines for risk stratification. Here we systematically review published evidences that should drive appropriateness in risk stratification, focusing on donor-specific antibodies against HLA and other antigens.

Natural IgM anti-leucocyte autoantibodies (IgM-ALA) regulate inflammation induced by innate and adaptive immune mechanisms

Little is known about the function of natural IgM autoantibodies, especially that of IgM anti-leukocyte autoantibodies (IgM-ALA). Natural IgM-ALA are present at birth and characteristically increase during inflammatory and infective conditions. Our prior clinical observations and those of other investigators showing fewer rejections in renal and cardiac allografts transplanted into recipients with high levels of IgM-ALA led us to investigate whether IgM-ALA regulate the inflammatory response. In this review, we show that IgM, in physiologic doses, inhibit pro-inflammatory cell function in-vitro. We also show in an IgM knockout murine model, with intact B cells and regulatory T cells, that there is more severe inflammation and loss of function in the absence of IgM after renal ischemia reperfusion injury and cardiac allograft rejection. Replenishing IgM in IgM knockout mice or increasing the levels of IgM-ALA in wild-type B6 mice significantly attenuated the inflammation in both of these inflammatory models that involve IFN-γ and IL-17. The protective effect on renal ischemia reperfusion injury Is mediated by IgM ALA as protection was lost when using IgM pre-adsorbed with leukocytes to remove IgM-ALA. We provide data to show that the anti-inflammatory effect of IgM is mediated, in part, by inhibiting TLR-4-induced NF-κB translocation into the nucleus and inhibiting differentiation of activated T cells into Th-1 and Th-17 cells. In additional studies, we also show that intra-peritoneal administration of IgM prevents NOD mice from developing autoimmune insulitis which also involves Th-1 and Th-17 cells. These observations highlight the importance of IgM-ALA in regulating excess inflammation mediated by both innate and adaptive immune mechanisms and where the inflammatory response involves Th-17 cells that are not effectively regulated by T regs, B regs, and IL-10. IgM-ALA may in part regulate inflammation by altering dendritic cell function, as dendritic cells pre-treated in-vitro with polyclonal IgM protected mice from renal IRI. The latter findings may have relevance for cell-based therapy.

Human casein alpha s1 (CSN1S1) skews in vitro differentiation of monocytes towards macrophages

Background

The milk-derived protein human Casein alpha s1 (CSN1S1) has recently been detected in blood cells and was shown to possess proinflammatory properties. In the present study, we investigated the effect of CSN1S1 on the differentiation of monocytes.

Methods

Primary human monocytes were stimulated with recombinant CSN1S1 and compared to cells stimulated with GM-CSF/IL-4 or M-CSF/IFNγ. Morphological changes were assessed by microscopy and quantification of surface markers of differentiation by FACS analysis. Phagocytic activity of CSN1S1 stimulated cells was measured by quantification of zymosan labeled particle uptake. The role of mitogen activated protein kinases for CSN1S1-induced differentiation of monocytes and proinflammatory cytokine expression was assessed by supplementation of specific inhibitors.

Results

CSN1S1 at a concentration of 10 μg/ml resulted in morphological changes (irregular shape, pseudopodia) and aggregation of cells, comparable to changes observed in M-CSF/IFNγ differentiated macrophages. Surface marker expression was altered after 24 h with an upregulation of CD14 (mean 2.5 fold) and CD64 (1.9 fold) in CSN1S1 stimulated cells. CSN1S1 treated cells showed a characteristic surface marker pattern for macrophages after 120 h of incubation (CD14^high, CD64^high, CD83^low, CD1a^low) comparable to changes observed in M-CSF/IFNγ treated monocytes. Furthermore, phagocytic activity was increased 1.4 and 1.9 fold following stimulation with 10 μg/ml CSN1S1 after 24 and 48 h, respectively. Early GM-CSF, but not GM-CSF/IL-4 induced differentiation of monocytes towards dendritic cells (DC) was inhibited by addition of CSN1S1. Finally, CSN1S1 induced upregulation of CD14 was impeded by inhibition of ERK1/2, while inhibition of the mitogen activated protein kinases JNK and p38 did not influence cellular differentiation. However, JNK and p38 inhibitors impeded CSN1S1 induced secretion of the proinflammatory cytokines IL-1b or IL-6.

Conclusions

CSN1S1 skews in vitro differentiation of monocytes towards a macrophage-like phenotype. Data is accumulating that functions of CSN1S1 are beyond nutritional properties and include immunomodulatory effects.

Autoantibodies to αS1-casein are induced by breast-feeding

Background

The generation of antibodies is impaired in newborns due to an immature immune system and reduced exposure to pathogens due to maternally derived antibodies and placental functions. During nursing, the immune system of newborns is challenged with multiple milk-derived proteins. Amongst them, caseins are the main constituent. In particular, human αS1-casein (CSN1S1) was recently shown to possess immunomodulatory properties. We were thus interested to determine if auto-antibodies to CSN1S1 are induced by breast-feeding and may be sustained into adulthood.

Methods

62 sera of healthy adult individuals who were (n = 37) or were not (n = 25) breast-fed against human CSN1S1 were investigated by a new SD (surface display)-ELISA. For cross-checking, these sera were tested for anti Epstein-Barr virus (EBV) antibodies by a commercial ELISA.

Results

IgG-antibodies were predominantly detected in individuals who had been nursed. At a cut-off value of 0.4, the SD-ELISA identified individuals with a history of having been breast-fed with a sensitivity of 80% and a specificity of 92%. Under these conditions, 35 out of 37 sera from healthy donors, who where breast-fed, reacted positively but only 5 sera of the 25 donors who were not breast-fed. The duration of breast-feeding was of no consequence to the antibody reaction as some healthy donors were only short term breast-fed (5 days minimum until 6 weeks maximum), but exhibited significant serum reaction against human CSN1S1 nonetheless.

Conclusion

We postulate that human CSN1S1 is an autoantigen. The antigenicity is orally determined, caused by breast-feeding, and sustained into adulthood.

Nature and nurture of catalytic antibodies

Immunoglobulins (antibodies) frequently express constitutive functions. Two such functions are nucleophilic catalysis and the reversible binding to B-cell superantigens. Constitutive or "naturally-occurring" antibodies are produced spontaneously from germline genetic information. The antibody structural elements mediating the constitutive functions have originated over millions of years of phylogenic evolution, contrasting with antigen-driven, somatic sequence diversification of the complementarity determining regions (CDR) that underlies the better-known high affinity antigen binding function of antibodies. Often, the framework regions (FRs) play a dominant role in antibody constitutive functions. Catalytic antibody subsets with promiscuous, autoantigen-directed and microbe-directed specificities have been identified. Mucosal antibodies may be specialized to express high-level catalytic activity against microbes transmitted by the mucosal route, exemplified by constitutive production of IgA class antibodies in mucosal secretions that catalyze the cleavage of HIV gp120. Catalytic specificity can be gained by constitutive noncovalent superantigen binding at the FRs and by adaptive development of noncovalent classical antigen or superantigen binding, respectively, at the CDRs and FRs. Growing evidence suggests important functional roles for catalytic antibodies in homeostasis, autoimmune disease and protection against infection. Adaptive antibody responses to microbial superantigens are proscribed underphysiological circumstances. Covalent electrophilic immunogen binding to constitutively expressed nucleophilic sites in B-cell receptors bypasses the restriction on adaptive antibody production, and simultaneous occupancy of the CDR binding site by a stimulatory antigenic epitope can also overcome the downregulatory effect of superantigen binding at the FRs. These concepts may be useful for developing novel vaccines that capitalize and improve on constitutive antibody functions for protection against microbes.

Natural immunoglobulins (contribution to a debate on biomedical education)

Immunology has contributed to biomedical education in many important ways since the creation of scientific medicine in the last quarter of the 19th century. Today, immunology is a major area of biomedical research. Nevertheless, there are many basic problems unresolved in immunological activities and phenomena. Solving these problems is probably necessary to devise predictable and safe ways to produce new vaccines, treat allergy and autoimmune diseases and perform safe transplants. This challenge involves not only technical developments but also changes in attitude, of which the most fundamental is to abandon the traditional stimulus-response perspective in favor of more "systemic" views. Describing immunological activities as the operation of a complex multi connected network, raises biological and epistemological issues not usually dealt with in biomedical education. Here we point to one example of systemic approaches. A new form of immunoblot (Panama blot), by which the reaction of natural immunoglobulins with complex protein mixtures may be analyzed by a special software and multivariate statistics, has been recently used to characterize human autoimmune diseases. Our preliminary data show that Panama blots can also be used to characterize global (systemic) immunological changes in chronic human parasitic diseases, such as malaria and schistosomiasis mansoni, that correlate with the clinical status.

Natural autoreactive B cells in transgenic mice reproduce an apparent paradox to the clonal tolerance theory

Naturally occurring autoreactive B cells are thought to be physically eliminated or rendered functionally silent through different mechanisms of tolerance. However, multireactive low affinity natural autoantibody-producing B cells seem to escape these mechanisms in normal adults and could constitute the B cell pool from which pathological autoantibodies can emerge. To analyze this apparent paradox to the clonal tolerance theory, we have made two transgenic mouse lines (mu(k), mudelta(k)) producing a natural low affinity multireactive human autoantibody. These models enable us to test both the central tolerance mechanisms (reactivity with single-stranded DNA) and the peripheral tolerance mechanisms after Ag administration. Not only are the multireactive B cells not deleted in the bone marrow, they circulate and remain in the periphery even after the prolonged administration of Ag, the presence of membrane IgD increasing the number of mature autoreactive B cells. Self-reactive B cells are shown to be autoantigen ignorant both in vivo and in vitro, but they are not anergic because they can be easily activated through both B cell receptor-dependent and -independent pathways. Thus, these mouse lines reproduce an apparent paradox to the clonal tolerance theory meriting further investigation of the biological significance of this phenomenon.

Autoreactivity of Human VH Domains from cDNA Libraries: Analysis with a Bacterial Expression System

Previous studies showed that VH domains of several anti-DNA Abs can bind DNA in the absence of VL. In the current work, we tested the VH autoreactive potential more generally, examining VH domains that did not come from known autoantibodies. Using a bacterial expression system, we produced 11 fusion proteins, each containing a VH domain and a B domain of staphylococcal protein A. The VH domains were coded in cDNA libraries from circulating B cells of healthy young adult humans. Thus, binding properties of the Ig molecules from which they came were unknown. The B cells had not been stimulated in vitro. Seven cDNA clones combined the frequently expressed VH3-23 gene segment with varied DH and JH segments. The other clones contained unmutated VH3-7, VH3-9, VH3-53, and VH4-39 segments. We compared these bacterial expression products with single-chain Fv, VH and VL domains of IgM mAb 18/2, a VH3-23-encoded, DNA-binding autoantibody. Submicromolar concentrations of 5 of the 11 VH domains bound to ssDNA. Those and one more also bound to immobilized poly(dT), and two bound to circular plasmid dsDNA. Soluble poly(dT) was the most potent inhibitor in competitive ELISA. Seven of the VH domains also bound to immobilized nuclear ribonucleoprotein, four to histone and none to thyroglobulin. Two interacted with the matrix of a Sephacryl S-100 column. The polyreactive autoantigen-binding properties of these VH domains raise the question of whether these properties may play a role in the formation of the VH repertoire of circulating B cells.

IgM class autoantibodies in human cord serum

It has previously been shown that human neonatal B lymphocytes in vitro can synthesize autoantibodies which typically are of IgM class, polyreactive and of low affinity and thought to represent natural autoantibodies. We screened 1034 cord serum specimens to find sera with elevated IgM levels; 98 such sera were further examined by an enzyme-linked immunosorbent assay (ELISA) to determine whether antibodies against a panel of autoantigens could be found. We detected low levels of IgM class antibodies against cardiolipin, pyruvate dehydrogenase, single-stranded DNA, thyroglobulin and Fc fragments of IgG as rheumatoid factors. The IgM concentration correlated with autoantibody levels. The specificity of the autoantibody assays was confirmed by inhibition tests. We conclude that several types of autoantibodies can be found in some sera of newborns and that increased IgM concentration of some neonates may reflect a polyclonal antibody response.

Tumour cell binding by a human monoclonal IgM antibody from the spleen of a non-tumour-associated patient is due to somatic mutations in the VH gene

Recently we described the occurrence of B cells producing polyspecific natural IgM with anti-tumour specificity in the spleen of non-tumour-bearing individuals as well as in fetal organisms. Immunoprecipitation and 2-D electrophoresis showed the binding of such antibodies to a 55-kD (pI 6.0) membrane surface glycoprotein. In vitro cultivation of human cancer cell lines in the presence of the purified IgM antibodies resulted in growth inhibition and complement-mediated cell lysis. Furthermore, the antibodies were shown to be able to induce MHC class I molecule expression on tumour cells. Because of this, a role for naturally occurring antibodies with anti-tumour specificity in preventing neoplasias had been suggested. We have constructed and expressed in Escherichia coli single-chain fragments (scFv: VH-linker-VL) derived from a polyspecific human monoclonal IgM autoantibody produced by a human x mouse heterohybridoma which was obtained from the spleen of an autoimmune patient. The mutated complementarity determining region (CDR) gene segments were replaced by the equivalent germ-line sequences and the CDR3 region was swapped for that from another polyspecific human natural antibody with no binding to tumours. Using these four scFv constructs for binding analyses and in vitro cultivation experiments we found: (i) scFv containing the mutated VH region of the original antibody were able to bind to tumour cells, to induce MHC class I molecule expression, and to inhibit tumour growth in a way similar to what had been described for the complete antibody; (ii) replacement of the mutated by the germ-line VH gene independently of the CDR3 to which it had been recombined, resulted in failure to bind to tumour cells. Nevertheless, other antigens (ssDNA, tetanus toxin) were still recognized, although with lower affinity. We discuss the significance of the replacement mutations in the VH gene CDRs, selected probably by B cell contact to an (auto)antigen, for generating a tumour binding capacity, not encoded by the germ-line gene.

Involution of the thymus revisited: immunological trade-offs as an adaptation to aging

An attempt was made, in previous theories, to find a unifying explanation for two phenomena of thymic involution: stress-induced reversible involution and age-related irreversible involution. It was postulated that in both cases involution is beneficial to the organism, as it serves to reduce the dangers of autoimmune reactions. The modified theory proposed here: (a) relates to the suggestions of I.R. Cohen and D.B. Young (Immunol. Today, 12 (1991) 105-109) and to those of S. Avrameas Immunol. Today, 12 (1991) 154-158) as to the usefulness of autoantibodies to the organism; (b) emphasizes the fact that self components undergo continuous changes throughout the life cycle of the organism, which in turn necessitates continuous adaptations to prevent autoimmune damage; (c) stresses the relevance of these adaptations to the process of natural selection; (d) brings experimental evidence to the effect that thymic involution will reduce the danger of autoimmune damage; and (e) suggests that the adaptations required to prevent autoimmune reactions with aging entail immunological compromises or trade-offs. These measures may by themselves cause autoimmune diseases, result in reduced resistance to neoplasia and to infectious diseases, particularly viral ones, and in accelerated aging.

Common idiotypes expressed on human, monoclonal, abnormal immunoglobulins and cryoglobulins with polyreactive autoantibody activities

Several human monoclonal immunoglobulins with the same autoantibody activity have been shown to have cross-reactive idiotypes (CRI). In this study, using polyclonal anti-idiotypic antibodies, we found that 28% of human monoclonal immunoglobulins with polyreactive autoantibody activity from myeloma, Waldenström's macroglobulinaemia and cryoglobulinaemia patients shared common idiotype(s). Furthermore, the latter were expressed on human and murine natural MoAbs (respectively in 12% and 22% of the clones tested) and on human IgG preparations used for therapeutic intravenous injections (IVIg) and which contain natural antibodies. These findings suggest that monoclonal immunoglobulins could arise from the proliferation of a clone that normally produces a natural antibody. The existence of common idiotype(s) between monoclonal immunoglobulins and IVIg could be relevant to the improvement noted after treatment with IVIg in patients suffering from peripheral neuropathies associated with monoclonal gammopathy.