Poly(Glu60Ala30Tyr10) (GAT)-induced IgG monoclonal antibodies cross-react with various self and non-self antigens through the complementarity determining regions. Comparison with IgM monoclonal polyreactive natural antibodies

Antibodies against Trypanosoma cruzi alkaline antigens are elicited in sera from acute but not chronic human chagasic patients

The aim of this work was to study the antibody response of acute and chronic chagasic patients against a Trypanosoma cruzi alkaline fraction (FI) in comparison with the reactivity against a T. cruzi acidic antigen, the main cystein proteinase of the parasite named cruzipain, and "natural" antigens. FI-specific antibodies were detected only during the acute phase of the infection and IgM was the main isotype produced, whereas cruzipain-specific antibodies were detected during all phases of the infection. By means of immunoblot and sequencing analysis we identified a 47-kDa FI proteic band recognized by IgM from acute chagasic patients as the T. cruzi glutamate dehydrogenase (GluDH). Furthermore, the antibody response against isolated GluDH showed similar characteristics as the one against FI. We also observed a strict association between the reactivity of IgM against FI and GluDH and IgM natural antibodies. However, reactivity against these alkaline antigens was not modified after absorption of natural antibodies in sera from acute chagasic patients, indicating that these parasite antigens are not recognized by the polyspecific natural antibodies. The most important goal of this report is that for the first time the T. cruzi antigen isoelectric point has been associated with its ability to trigger immunological memory, raising a novel antigen property that should be considered in the selection of antigens used in Chagas' disease diagnostic test and in the design of a vaccine against T. cruzi infection.

The IgG2a/IgA produced by the murine T560 B lymphoma that arose during a graft-versus-host reaction is polyreactive and somatically mutated

In mice undergoing a graft-versus-host (GVH) reaction, donor T cells responding to the host's MHC antigens induce polyclonal activation of the host's B cells and secretion of their antibodies and autoantibodies. T560, a CD5- B lymphoma that arose in the gut-associated lymphoid tissue (GALT) of a (B10 x B10.H2aH4(b)pWts) F1 hybrid mouse that had been injected with parental B10.H2aH4b splenocytes, is of particular interest because it produces switched, heavily mutated, but, nevertheless, polyreactive immunoglobulin. T560 bears and contains IgG2a but switches to IgA spontaneously. The T560 Ig variable region is encoded by a V186.2-related VH gene, juxtaposed to DFL 16 and J(H)1, and by a Vkappa gene of the Vkappa 4/5 group juxtaposed to Jkappa1. Both VH and VK are heavily mutated. The IgA binds to polystyrene, to p-azophenyl-phosphorylcholine (PC)-conjugated keyhole limpet hemocyanin (KLH) (PC-KLH), to 2,4,6 trinitrophenylated (TNP)-KLH and to human TNF-beta but not to KLH, human TNF-alpha, or any of several other Ags tested. Hapten inhibition experiments indicate that the polystyrene, PC- and TNP-binding sites do not overlap. The switched isotypes and heavy load of somatic mutations found in the T560 IgG2a/IgA suggest that T cell-dependant somatic selection of the T560 precursor B cell may have been superimposed on polyclonal B cell activation originally associated with the GVH.

Specificity and function of "natural" antibodies in immunodeficient subjects: clues to B cell lineage and development

The origin of natural antibodies has long been a subject of controversy. Polyreactive natural antibodies recognize multiple ligands and are thought to arise from B1 B cells. Natural antibodies against carbohydrate antigens such as Gal alpha 1-3Gal or against blood groups A and B are thought to be "elicited" by gut bacteria, but their origin is uncertain. To explore the origin of naturally occurring anticarbohydrate antibodies, the specificity and function of the xenoreactive antibodies and isohemagglutinins were investigated in immunodeficient subjects. Subjects with defects in T cell-dependent antibody synthesis had normal levels of xenoreactive natural antibodies, most of which, like xenoreactive antibodies from normal individuals, were specific for Gal alpha 1-3Gal. On the other hand, some subjects with hyper-IgM syndrome who were able to synthesize abundant quantities of xenoreactive antibodies and polyreactive antibodies were devoid of anti-Gal alpha 1-3Gal antibodies. These results suggest that the lineages of B cells giving rise to anti-Gal alpha 1-3Gal antibodies and isohemagglutinins are distinct from B1 B cells or at least exist at a more "advanced" stage of development than those B1 B cells that give rise to polyreactive antibodies. The findings also suggest that B cells which synthesize anti-Gal alpha 1-3Gal antibodies and isohemagglutinins may be distinct from B2 B cells or exist at a more "primitive" stage of development than B2 B cells that synthesize elicited antibodies in normal individuals.

Effect of temperature on the reactivities of polyreactive and monospecific monoclonal IgG antibodies

In this study, the reactivities of two groups of murine monoclonal antibodies (mAbs) of the IgG isotype were compared by ELISA at various temperatures (Ts) (range: 4-56 degrees C). The first group was constituted of 4 polyreactive mAbs that reacted with various antigens (Ags), such as actin, myosin and tubulin. The second contained 3 commercially available monoreactive mAbs specific to actin, myosin or tubulin. The binding of the monospecific mAbs to their Ags was modified only slightly at the other Ts compared with binding at 37 degrees C. In contrast, the activities of the polyreactive IgGs were considerably modified depending upon the T during incubation on Ag. In a second series of experiments, the effects of the T of the washes and conjugate incubation on the mAb/Ag interaction were evaluated. In these experiments, all steps and incubations were carried out at 37 or 4 degrees C. The values were then compared to those obtained when the washes and conjugate incubation were performed at room temperature. These two protocols generated very little difference in terms of monospecific mAbs. For polyreactive IgG, the values were generally lower when the incubations were carried out at 4 degrees C. However, on the whole, the effect of the T of the washes and conjugate incubation was negligible when the mAb/Ag complex had already formed on the polystyrene plate. Furthermore, at 4 degrees C, 2 of the polyreactive mAbs behaved like monospecific antibodies, while the other 2 remained polyspecific. It can be concluded from these experiments that the reactivities of polyreactive mAbs are more T-sensitive than those of monoreactive mAbs. This seems to indicate that they may possess a more plastic structure and thus may more easily undergo deformation when subjected to non-physiological conditions. In addition, the fact that the polyreactive mAbs showed the same variations for the 3 Ag tested suggests that the same paratope could be involved in all reactions.

Chagas' disease: polyspecificity of antibodies against Trypanosoma cruzi acidic antigens

The aim of this work was to study the reactivity of chagasic patient sera against a panel of natural antigens and its relationship with the immune response against T. cruzi acidic antigens. The presence of IgG and IgM antibodies reactive with myosin, myoglobin, actin and thyroglobulin was investigated in sera with positive serology for Chagas' disease classified into groups (G) I, n = 7, with normal electrocardiogram (ECG) and no signs or symptoms of the disease; GII, n = 7, with ECG abnormalities but without cardiomegaly and GIII, n = 7, with cardiomegaly and congestive heart failure. Healthy individual sera were analyzed in parallel as controls. In the three groups of chagasic patients, a high proportion of sera exhibited an enhancement of IgG response anti actin ranging from 71 to 100%. IgM against this antigen was found positive in GI, 21%; GII and GIII, 57%. The antibodies binding to myosin and myoglobin were mainly of IgM type. When myosin was assayed, the frequency of reactive sera was gradually diminished as heart involvement increased: GI 57%, GII 28% and GIII 14%. Only IgG antibodies against thyroglobulin were detected in the three groups of chagasic patients ranging from 43 to 86%. IgG natural antibodies showed to be polyreactive, since a diminished reactivity against each one of the natural antigens assayed and against T. cruzi acidic antigens (FIV) was observed in the sera absorbed with any of the selected antigens irrespective of the absorbing ones. Moreover, the antibodies against FIV parasite's antigens purified by immunoabsorption showed a similar reactivity with FIV, myosin and actin, and a slight lower reactivity with thyroglobulin. These results indicate that in chagasic patients, the specific humoral response against FIV is associated with an increase of the natural autoantibodies along with their polyspecificity.

Effects of pH or ionic strength on the reactivities of mono- and polyspecific IgG antibodies

The reactivities of mono- and polyspecific mouse monoclonal antibodies (mAb) were compared by ELISA using immobilized antigens under different conditions, varying the pH or the NaCl concentration. The monospecific group was composed of 6 IgG directed against Staphylococcus aureus capsular polysaccharides and of 3 IgG specific to actin, myosin or tubulin. These antibodies were compared with 6 polyreactive mAb also of the IgG isotype. Marked differences were noted between the reactivities of the mono- and polyreactive IgG. pH variations had little or no effect on the reactivity of monospecific mAb to polysaccharides or to proteins. In contrast, the binding of polyreactive mAb was dependent on the pH, and the profile differed for each antigen. The NaCl concentration had opposite effects on mono- and polyreactive mAb: the binding of almost all the monoreactive mAb was increased at high NaCl concentration, while it was decreased for polyreactive mAb. In contrast, the effects of varying the pH or ionic strength on the coated antigens were negligible. The variation coefficients calculated for the pH and NaCl concentration were higher for the polyreactive mAb under study, which seems to indicate that electrostatic interactions and charged residues might be more important for these mAb than for the monoreactive ones. This characteristic might be one explanation for the particular properties of these polyreactive antibodies.

Reactivity and structure of a mouse anti-F(ab')2 IgM. Comparison of its variable region sequences with those of a structurally close polyreactive natural IgM

IE12 is a monoclonal IgM with strong anti-F(ab')2 activity that inhibits the binding of normal mouse IgG to self antigens. In this study, we found that this IgM was also reactive with several monoclonal antibodies (mAbs), myeloma proteins and B lymphocytes from normal BALB/c mouse. The nucleotide sequences of the variable region of the heavy and light chains of IE12 were determined, and compared to those of another mAb already described in the literature. This mAb uses the same light chain and also the same VH, D and JH segments, but unlike IE12, is polyreactive. The comparison of the amino acid composition of these two mAbs and of the computer predictions for their structure and hydrophilicity indicated that the most striking difference between them was located in the third complementarity determining region (CDR3) of the heavy chain. Indeed, they used the same D segment but translated in two different reading frames, leading to different amino acid compositions. The CDR3 of IE12 contains aliphatic amino acids, while that of the polyreactive IgM does not. In addition, IE12 has two prolines, one at each at each extremity of its D segment, that could confer a certain rigidity to this region. Finally, the CDR3 of IE12 is predicted to be hydrophobic, while the one of the polyreactive IgM is predicted to be hydrophilic and more flexible, suggesting that the hydrophilicity and the flexibility of this region might be critical for polyreactivity.

Anatomy of the antibody molecule

The structures of the various regions of an antibody molecule are analysed and correlated with biological function. The structural features which relate to potential applications are detailed.

Autoimmunity and selected environmental factors of disease induction

Autoimmune diseases may be induced by physical and/or chemical environmental factors. A review of the available literature on mercuric chloride, iodine, silicone, anilides, L-tryptophan, vinyl chloride, and canavanine suggests three general mechanisms by which they may induce disease. First, oxidative damage probably is a frequent process involved in disease induction and pathogenesis. Second, certain compounds also may generate antigen-specific immune responses that could then cross-react with self-tissues. Other xenobiotics might bind to self-tissues and increase self-tissue immunogenicity. Third, physical and chemical agents may also modulate the immune system. Finally, in response to controversies surrounding the influence of human activities on global climate changes, the immunosuppressive effects of ozone and ultraviolet radiation are discussed.

Correlation of antibody multireactivity with variable region primary structure among murine anti-erythrocyte autoantibodies

A high proportion of the antibodies in the preimmune repertoire bind to several unrelated antigens and are considered to be multireactive. This property is reportedly associated with the antibodies produced by CD5+ B lymphocytes. Because many antibodies specific for bromelain-treated mouse red blood cells (BrMRBC) derive from CD5+ B cells, we tested monoclonal antibodies of this specificity for multireactivity. Two variable region combinations, VH11/V kappa 9 and VH12/V kappa 4, account for greater than 80% of this repertoire, but none of these antibodies exhibited a multireactive phenotype. In contrast, three anti-BrMRBC binding antibodies belonging to the J558 family (BrM1, BrM8, and CH12) showed varying degrees of multireactivity, and bound both highly negatively and positively charged antigens. The amino acid sequences of the VH regions of these antibodies are highly homologous (greater than 85% identical) and they possess large VH-D-J junctions with extensive N-region insertions. The kappa chains of two of these antibodies utilize an identical V kappa gene segment, while the third uses a very different V kappa with only 50% homology. The entire H chain V regions of these antibodies are unusually basic, with isoelectric points of 9.5-10, a feature which might be important in promoting interactions with acidic epitopes. The multireactive antibodies also contain regions with a high concentration of hydroxylside chain amino acids, especially in their VH-D-J junctions. This region also contains acidic amino acid residues, which may be important in binding of positively charged epitopes. We propose that an open, accessible binding site and a charge polarity may be features which facilitate the binding of charged epitopes, providing a structural basis for multireactivity of at least some antibodies.

Visualization of natural autoantibody polyreactivity by rotary metal-shadowing electron microscopy

Immune complexes formed by mouse polyspecific natural autoantibodies and various structurally different antigens, such as DNA, tubulin and myosin, were analysed by rotary-shadowing electron microscopy. Each of the four natural IgM autoantibodies studied (E7, D23, 3C3 and M2-9) recognized multiple epitopes on the myosin molecule. These results, confirmed by immunoblotting experiments using myosin subfragments as antigens, strikingly contrasted with those obtained with an induced myosin-specific IgG antibody which interacted with a single myosin antigenic site. Based on the measurements of the antibody position on the antigen, made on a series of electron micrographs, two negatively charged myosin peptides were prepared by solid phase synthesis. Polymeric forms of one of the two peptides interacted with the positively charged CDR part of E7 and inhibited the binding of E7 and M2-9 to myosin. The importance of charge in the observed cross-reactivities was further supported by enzyme immunoassays showing that most, but not all, antigen/natural autoantibody interactions were sensitive to increasing concentrations of NaCl.

Natural autoantibodies: from 'horror autotoxicus' to 'gnothi seauton'

The immune system of normal unimmunized animals is characterized by the presence of B cells synthesizing and secreting mainly polyreactive, but also monoreactive, IgM and IgG natural antibodies that can react with a variety of self constituents. These antibodies, like the autoantibodies appearing in several immunopathological states, use the same genetic elements as the antibodies directed against environmental antigens, and seem to be encoded by unmutated germ-line genes. Accumulating evidence indicates that these natural auto-antibodies exert various biological roles, both related and unrelated to the immune system. In this article, Stratis Avrameas proposes that natural auto-antibodies, by interacting with the large number of self constituents present in an organism, establish an extensive dynamic network that contributes to the general homeostasis of the organism.