IgM-rheumatoid factors cross-reactive with IgG and a cell nuclear antigen: apparent 'masking' in original serum

Non-immunoglobulin serum proteins prevent the binding of IgG from normal rats and from rats with Th2-mediated autoimmune glomerulonephritis to various autoantigens including glomerular antigens

It is now well established in normal humans and mice that purification of IgG from serum unmasks their autoantibody activity. Mercuric chloride (HgCl2) induces in Brown-Norway (BN) rats a Th2-dependent polyclonal B cell activation, a huge increase in serum IgE and IgG1 concentrations, the production of numerous autoantibodies and an autoantibody-mediated glomerulonephritis. In the present study we have compared the IgG autoantibody activity in the serum and in the purified IgG fraction from normal and HgCl2-injected BN rats. IgG autoantibodies were found to be masked in normal serum by non-immunoglobulin (nonIg) serum proteins and, provided these IgG did not encounter normal serum proteins, they could bind to glomerular antigens as assessed by immunofluorescence in a unilateral perfused kidney model. As a consequence of HgCl2-induced polyclonal activation of B cells, IgG autoantibodies were no longer complexed to non-Ig serum proteins, they were easily detected in the serum and could therefore reach their glomerular target. However, these autoantibodies could still be blocked by normal non-Ig serum proteins not only in vitro but also in a unilateral perfused kidney model so that their binding to glomerular antigens could be prevented. These findings indicate that the ratio between autoantibody level and the amount of non-Ig serum proteins may be crucial in autoantibody-mediated autoimmune diseases.

Multiple antigen recognition by individual human monoclonal antibodies of rheumatic disease patient origin

We tested by Western blot several thousand antibody-secreting human cell lines immortalized by hybridoma fusion or Epstein-Barr virus transformation of peripheral blood lymphocytes from patients with systemic lupus erythematosus or mixed connective tissue disease. The blots utilized total human Jurkat cell extract as the antigen. More than 20% of these established lines produced antibodies which recognized multiple bands on the blots, frequently 50 bands or more. Experiments were performed to rule out the possibility of the bands being the result of mixed cell populations or nonspecific antibody-antigen binding. Cloning of these cell lines failed to alter the Western blot patterns produced, indicating that the populations were monoclonal. Antibody eluted from a number of the different single blot bands showed the same ability to reproduce the multiple band pattern, thus revealing the presence of only one antibody. Western blots performed in the presence of specific and nonspecific inhibitors demonstrated the ability of the antibody to specifically recognize and bind to certain antigens. Binding did not result from indiscriminate sticking of IgM molecules to the nitrocellulose paper. The patterns of multiple antigen recognition were not due to antigen degradation. Additionally, enzyme linked immunosorbant assays revealed binding of the monoclonal antibodies to specific antigens, and the antibodies failed to recognize commonly crossreactive antigens such as DNA, histone, poly-L-lysine, glycophorin, and serum glycoproteins. The patterns of multiple antigen binding to a large number of polypeptides are therefore due to single antibodies, and the binding is specific.

Do polyclonal rheumatoid factors carry an 'internal image' of cytomegalovirus, Epstein-Barr virus and nuclear antigens?

Rabbit antisera have been prepared against isolated rheumatoid factors (RF's). It was considered that RFs are anti-idiotype antibodies and that the anti-RF antisera had anti-anti-idiotype specificity. Furthermore, it was considered that the RF's carry an "internal image" of the putative "antigen X" and that the rabbit antisera would have specificity for this "antigen-X". Reactions of the rabbit antisera with the early and late antigens of CMV, EBV antigens and nuclear antigens suggest that there may be an "internal image" of these antigens in rheumatoid factor molecules and that they all may be related to the immunogenesis of RF.

Characterisation of non-histone nuclear proteins cross reactive with purified rheumatoid factors

In order to examine the interactions between isolated rheumatoid factors (RFs) and cell nuclear antigens we have prepared 10 RFs by affinity chromatography against IgG coupled to Sepharose. Of these, seven cross reacted with cell nuclei on indirect immunofluorescence. The nuclear antigen appeared to be DNA histones by indirect immunofluorescence on rat liver, though on immunoblotting the rheumatoid factors also reacted with three non-histone polypeptides which were identified in the soluble fraction of nuclear extracts. We were unable to show any relationship between these polypeptides and rheumatoid arthritis nuclear antigen. These reactions represent a hitherto unrecognised phenomenon, which extends the range of antigens recognised by rheumatoid factors. We suggest that the immunopathogenic significance of RFs may not be restricted to their reactivity with IgG, and that non-histone nuclear proteins merit further investigation.

Autoantibodies to anti-DNA with anti-allotypic and anti-idiotypic specificities in (NZB X NZW)F1 mice

The monoclonal A52 (IgG2b, kappa) anti-DNA autoantibody represents a major cross-reactive idiotype in the murine and human autoimmune response to DNA. Examination of sera and purified IgG derived from (NZB X NZW)F1 mice showed that these mice develop an age-dependent binding reactivity with the pure anti-DNA IgG. Three monoclonal antibodies possessing this reactivity were prepared from unprimed female (NZB X NZW)F1 mice. One of these monoclonal antibodies appeared to be directed against allotypic determinants present in the NZB IgG2b; the other two antibodies exhibited a marked preference for idiotypic determinants of the A52 IgG. The IgG anti-allotype and anti-idiotype activities in (NZB X NZW)F1 mice may, therefore, represent the products of a deregulated immune system and/or constitute the normal elements of a functional immune regulation system.

Multiple autoantigen binding capabilities of mouse monoclonal antibodies selected for rheumatoid factor activity

We report that approximately 1/4 of monoclonal rheumatoid factors produced by hybridomas derived from fusions of spleen cells from MRL/lpr/lpr mice with systemic lupus erythematosus (SLE) and arthritis exhibited multiple reactivities with other autoantigens, including dDNA , histones, and/or cytoskeletal-cytoplasmic elements. The patterns of reactivities of most of these clones differed, indicating that each had a separate B cell ancestor. Studies with eluted antibodies demonstrated that a single species of antibody molecules was responsible for the observed multiple reactivities. Inhibition experiments suggested that an antibody combining site may be large enough to accommodate dissimilar epitopes. These findings may provide further insights into the generation and extent of antibody diversity as well as the etiopathogenesis of systemic autoimmune diseases.

Rheumatoid factors in 129XB recombinant inbred strains. Igh-1-linked control of allotypic and isotypic specificities

To examine the role of autologous IgG in the induction of murine rheumatoid factors (RF) we have analyzed the allotypic specificity of anti-IgG2a RF in recombinant inbred strains derived from 129/Sv (Igh-1a) and C57BL/6 (Igh-1b) mice. In five of six Igh-1a strains, anti-IgG2a RF reacted with IgG2aa but failed to react with IgG2ab. In contrast, isotype-specific RF, which reacted equally well with a and b allotypes of IgG2a, represented the major RF species in one Igh-1a and all five Igh-1b strains tested. An additional form of RF specific for IgG2ab and not reactive with IgG2aa was detected in one Igh-1b strain. RF specific for a give allotype was thus only found in the presence of that allotype, which strongly suggests the involvement of autologous IgG in the induction of mouse RF synthesis. The specificity of RF was apparently further controlled by genes linked to but different from the Igh-C locus, as indicated by the absence of IgG2aa-specific RF in one of the 6 Igh-1a strains tested. Because this strain, 129XBG, has been shown to express idiotypic markers characteristic of Igh-1b mice, it is likely that the genes, which in the presence of a given allotype induce the production of isotype rather than allotype-specific RF, are identical to those that control the expression of idiotypes. Evidence was also obtained to indicate that Igh-1-linked genes influence the isotypic specificity and the isotype of RF itself: IgA anti-IgG2a predominated in Igh-1a strains and IgM anti-IgG1 in Igh-1b strains. Interestingly enough, total IgA and IgG2a levels also were higher in Igh-1a than in Igh-1b strains.

Binding of isolated rheumatoid factors to histone proteins and basic polycations

A fluorimetric immunoassay has been used to assess reactivity of rheumatoid factor (RF) with both histone proteins and other basic polycations (poly-L-lysine, poly-L-ornithine, and protamine) bound to an immobilised tyrosine-glutamic acid polyanionic copolymer. Isolated RF preparations can bind to histone proteins in this assay, notably to H3 and H4 histones, and this activity was always masked in the original whole seropositive sera. Binding of isolated RF was often noted also to the other large-molecular-weight basic polycations.

Antibody to intermediate filaments of the cytoskeleton

IgM antibodies against cultures of intermediate filaments (IMF) of the cytoskeleton were demonstrated by immunofluorescence in the sera of 94 (80%) of 118 patients with seropositive rheumatoid arthritis. These antibodies reacted with IMF in cultures of both human fetal fibroblasts and laryngeal carcinoma (HEp2) cells. Of 10 patients from whom paired synovial fluids were also available 8 had anti-IMF antibodies in both serum and fluid. In seronegative RA the incidence of anti-IMF was 40%, in ankylosing spondylitis 25%, in osteoarthrosis 16%, and in normal subjects 14%. Only a minority of RA sera positive for anti-IMF antibodies were also positive for smooth muscle antibody. Absorption experiments suggest that in RA anti-IMF is directed at the intermediate filament protein, vimentin.

Identification of syncytiotrophoblast-associated IgG in term human placentae

A mouse monoclonal antibody (H318) with specificity for an antigenic determinant in the C gamma 2 domain of human IgG, which was produced following immunisation with purified syncytiotrophoblast plasma membranes, has been shown to stain strongly human syncytiotrophoblast in immunofluorescence on cryostat section of term placental villous tissue. The staining was more pronounced with this antibody than with other monoclonal antibodies to the C gamma 2 domain of human IgG produced following the same immunisation or immunisation with isolated IgG. It appears that the H318 antibody may recognise an antigenic determinant which is enhanced on IgG that is associated with syncytiotrophoblast, possibly resultant from its interaction with IgG-binding structures.

False RIA IgM titres to herpes simplex virus and cytomegalovirus: factors causing them, and their absorption by protein A-Sepharose/IgG-protein A-Sepharose

A method for the absorption of false radioimmunoassay (RIA) IgM titres against herpes simplex virus (HSV) and cytomegalovirus (CMV) is presented. The serum specimens were absorbed by a mixture of protein A-Sepharose and protein A-Sepharose saturated with normal human gamma globulin (PAS/IgG). The detection of rheumatoid factor of IgM class (IgM-RF) as well as antinuclear antibodies (ANA) of both IgM and IgG class by solid-phase RIA is also described, and their role in the false IgM results was studied. It was found that the PAS/IgG absorption removed 50-90% of both IgM-RF and total IgG. The reduction of IgM-ANA clustered at 50-90% or nothing, whereas the reduction of IgG-ANA was approximately 50%. The studies with HSV and CMV antigens indicated that the removal of false IgM titres was more effective than the removal of each of these four factors. It was concluded that the IgM-RF titres alone were not sufficiently high to explain the false IgM results, but the ANA activity probably contributed.

The reversal immune surveillance hypothesis: part II

The first part of the reversal immune surveillance hypothesis (RISH. I) describes the conceptual framework of the immune system as a homoeostatic mechanism for the control of cell differentiation and replication. The thymic dependent lymphocytes (T-cells) are considered to be tissue specific and identify aberrations in the cell surface pattern (antigens), that represent that particular cell type. The T-cells may then recruit antibody forming B-lymphocytes (B-cells) to produce antibodies (humoral response) to the cell surface antigens in order to return the cell surface pattern to its correct state. The antigens may also be removed from the cell surface as immune complexes by the complement system, which under normal conditions does not cause cell lysis. The cellular arm of the immune system, that of killer cells or activated macrophages are considered to be primarily involved with tissue remodelling. Whether or not the humoral or cellular arm of the immune system is activated depends upon the antigens displayed by the stimulating cell. The proposed system, which is self monitoring, is considered to have evolved from the invertebrates through to the vertebrates to become more complex in the mammals. Therefore the immune system is considered to be based on the identification of self and self-foreignness, rather than on foreignness per se.

Human autoantibodies that react with both cell nuclei and plasma membranes display specificity for the octamer of histones H2A, H2B, H3, and H4 in high salt

Sera of some patients with systemic lupus erythematosus and related diseases contain a polyclonal antibody population (cross-reactive antinuclear antibodies [X-ANA]) that react specifically with both core mononucleosomes and plasma membranes of viable nucleated cells. Native mononucleosomes and nucleosome cores assembled from long DNA and the inner histones were indistinguishable in terms of inhibition of binding of X-ANA to nuclei of tissue sections and to polynucleosomes on the walls of plastic tubes. In contrast, mononucleosomes selectively depleted of histones H2A and H2B did not inhibit these reactions. A method was developed for isolation of X-ANA from serum that took advantage of the dual specificity of these antibodies. Immunosedimentation in sucrose density gradients revealed that 125I-labeled Fab' fragments of highly pure X-ANA formed complexes with the inner histones H2A, H2B, H3, and H4 in 2 M NaCL, but not in 0.15 M salt. These results indicate that X-ANA recognize an epitope of the inner histone in 2 M salt, and that in 0.15 M NaCL this epitope is not formed unless the histones interact with DNA to generate a nucleosome structure. Furthermore, in light of the previous demonstration that the epitope is destroyed by trypsin, it may be localized in the N-terminal region of histone H2A or H2B.

IgM-rheumatoid factors cross-reactive with IgG and a cell nuclear antigen: immunopathological implications?

The cross-reaction of IgM-rheumatoid factors (IgM-RF) with a cell nuclear antigen has been further investigated by immunofluorescence procedures. This reaction appears to be optimal at pH 8-9, and fails to occur at pH 6.5. No evidence was obtained by immunofluorescence that IgM-RF bound to the cell nuclear antigen fixes complement. It would appear that the nuclear reactivity of IgM-RF may be of limited immunopathological significance, though this reaction is of note in understanding the behavioural nature of rheumatoid factors.

Evidence for a subset of rheumatoid factors that cross-react with DNA-histone and have a distinct cross-idiotype

Cross-reactivity of a monoclonal rheumatoid factor with an antigen present on IgG and DNA-nucleoprotein was demonstrated, and evidence presented that the combining site of the antibody was involved in the reaction. The antigen on the DNA-nucleoprotein was shown to involve both DNA and histone fraction H2A + H2B and was trypsin sensitive. The relative binding affinity of the antibody appeared to be greater for IgG than the DNA-histone antigen. Similar polyclonal cross-reactive rheumatoid factors were found in a variety of diseases. A high incidence was found among patients with rheumatoid arthritis and mixed connective tissue disease. None were detected in patients with systemic lupus erythematosus and idiopathic cryoglobulinemia. Studies on one representative isolated polyclonal rheumatoid factor demonstrated the same reactivity with DNA-histone H2A + H2B as the monoclonal antibody. Cross-idiotype studies using antigen-binding inhibition methods demonstrated the same cross-idiotype on the polyclonal and the monoclonal rheumatoid factor which reacted with DNA-histone. This cross-idiotype was shown to be distinct from the cross-idiotypes previously demonstrated on monoclonal IgM proteins with anti-gamma-globulin activity.

A haemagglutination method for detection of rheumatoid factor using preserved erythrocytes covalently coated with human IgG

The preparation and use of a new haemagglutination assay for rheumatoid factor using preserved erythrocytes covalently coated with human IgG is described. Test serum heat inactivation or adsorption with uncoated erythrocytes is not required. This human IgG-coated erythrocyte agglutination test (H/CEAT) appears stable and specific, is suitable for routine determinations of serum IgM-rheumatoid factor, is simple to perform and compares favourably in these properties with either the Rose-Waaler or latex agglutination assays for rheumatoid factor.