Relation Between Gm Types and Hemagglutinating Substances in Rheumatoid Sera

Specificity of the reaction between rheumatoid factors and gamma globulin

Rheumatoid factors in the sera of patients with rheumatoid arthritis appear to be specifically directed against genetically determined "antigens" in human γ-globulin. At least eight rheumatoid factors of differing specificity exist; usually several are present in combination in the same serum. The different rheumatoid factors can be readily detected through their pattern of reactivity with anti-Rh antibodies from different individuals. Rheumatoid factors in diseases other than rheumatoid arthritis were found to have a more restricted specificity, contrasted to the broader reactivity of the factors in most rheumatoid arthritis sera. A specificity similar to that for incomplete antibodies was not demonstrated for the reaction of rheumatoid factors with aggregated γ-globulin or with γ-globulin to form the "22S complex." In certain instances, using the anti-Rh system, rheumatoid factors were found to react poorly with the patient's own γ-globulin, compared to that of other individuals of different genetic γ-globulin types. These results, as well as additional indirect evidence, indicate that the rheumatoid factors can possess isospecificity. However, a certain degree of autospecificity was also found which was most clearly evident through complex formation with the patients own γ-globulin and in the reaction with aggregates. The relevance of these findings to possible isoantibody as well as autoantibody concepts is discussed.

Rheumatoid factors from patients with rheumatoid arthritis react with tryptophan 60 and 95, lysine 58, and arginine 97, on human beta 2-microglobulin

OBJECTIVE

To define precise epitopes on human beta 2-microglobulin (beta 2m) reacting with polyclonal IgM rheumatoid factors (RF) from patients with rheumatoid arthritis (RA).

METHODS

Ten polyclonal RF were tested for their human beta 2m epitope-binding specificities using the entire 99-amino acid sequence synthesized as overlapping 7-mers in an enzyme-linked immunosorbent assay. Glycine substitution for each residue within RF-reacting linear regions was employed to define major reactive sites.

RESULTS AND CONCLUSION

Major beta 2m residues contributing to RF reactivity were tryptophans at positions 60 and 95, lysine at 58, and arginine at position 97.

Conformational dependency of human IgG heavy chain-associated Gm allotypes

Human IgG allotypic markers Gm(a)[Glm(1)], Gm(x)[Glm(2)]; Gm(f)[Glm(4)], Gm(b)[G3m(5) and (11)] and Gm(g)[G3m(21)] were studied after chemical modification of IgG histidines by diethylpyrocarbonate, tyrosines by N-acetylimidazole and lysines by formaldehyde and sodium borohydride. Degrees of substitution were estimated by trinitrobenzenesulfonic acid assay. IgG of known Gm phenotype isolated from serum of hyperimmune anti-tetanus toxoid donors was studied. Histidyl modification resulted in virtually complete loss of Gm(a) and Gm(g) antigenicity but preservation of Gm(x), Gm(b) and Gm(f). Reconstitution of the histidyl residues using hydroxylamine resulted in virtually complete restoration of Gm(a) and Gm(g) antigenicity. Histidine modification resulted in no significant decrease in ELISA anti-tetanus antibody activity. Alteration of tyrosyl residues using N-acetylimidazole considerably diminished Gm(a) and Gm(f) expression. This effect was reversed by hydroxylamine treatment. Moreover, chemical alteration of tyrosyl residues produced a complete loss of Gm(g) antigenicity which was only partially restored after deacylation. A urinary H chain fragment containing the VH region directly linked to C gamma 3 which contained the Gm(a) specific and Gm(x) specific amino acid residues was positive for Gm(a) but negative for Gm(x). Another urinary H chain fragment containing only the C gamma 3 domain was negative for both Gm(a) and (x). These findings indicate that Gm allotypic markers may depend on conformational determinants in which strongest expression for Gm(a) and (x) depends on structures expressed by C gamma 3 linked to C gamma 2 domains. Although RFs react with the region encompassing the C gamma 2-C gamma 3 interface, Gm-specificities of such reactions are affected allosterically through single or double amino acid substitutions at a relatively distant site.

Monoclonal IgM rheumatoid factors generated from synovial B cells of rheumatoid arthritis patients react with beta 2-microglobulin. Monoclonal RF react with beta 2m

Four of 15 monoclonal human IgM rheumatoid factors (RF) derived from synovial B cells of patients with rheumatoid arthritis showed positive ELISA reactions with human beta 2-microglobulin. These findings were different from those previously noted using IgM RF derived from monoclonal Waldenstrom's paraproteins or the IgM components of mixed cryoglobulins, and resembled the anti-beta 2 microglobulin specificity of polyclonal IgM RF from patients with rheumatoid arthritis. Reactions of monoclonal IgM synovial RF with overlapping 7-mers of beta 2m sequence indicated major regions of positive reactivity at positions 57-64 and 89-95 which were maintained in the presence of high salt (300 mM NaCl) conditions. Glycine substitution of each residue within RF-reactive beta 2m regions indicated that tryptophanes at position 60 and 95, lysine at 58, phenylalanine at 62, valine at 93 and arginine at 97 constituted important single amino acids for the reactive epitopes. These findings indicate that clonally restricted human IgM RF derived from diseased tissues of patients with RA show anti-beta 2m reactivity similar to polyclonal RF from the same patients. This particular fine specificity is not present in monoclonal RF derived from patients with Waldenstrom's or mixed cryoglobulins showing anti-gamma-globulin activity.

Rheumatoid factors react with Fab fragments of monoclonal antibodies to herpes simplex virus types 1 and 2 Fc gamma-binding proteins

Human polyclonal IgM rheumatoid factors (RF) were tested in an enzyme-linked immunosorbent assay with monoclonal antibodies (MAb) (II-481 and B10/A8) to glycoprotein E (gE), the Fc gamma-binding protein of herpes simplex virus type 1 (HSV-1), as well as with MAb 88-S to gE of HSV-2. Most of the RF reacted with II-481 and 88-S. Positive reactions were recorded for RF reacting with whole MAb II-481 and 88-S, as well as with their Fab, but not their Fc, fragments. Human monoclonal IgM RF isolated from mixed cryoglobulins showed a similar profile, with reactivity for both whole MAb II-481 and 88-S and for their Fab fragments. Reactivity with MAb to gE was observed regardless of the Gm specificity of the polyclonal RF and the cross-reactive idiotypes (6B6, 17.109, or G6) of the monoclonal RF. No positive reactions were noted between protein A and Fab fragments of any of the anti-gE MAb. These findings indicate that many RF may bear the internal image of the Fc gamma-binding regions of 2 different herpesviruses: HSV-1 and HSV-2.

Immunogenetic markers as probes for polymorphism, gene regulation and gene transfer in man--the Gm system in perspective

The genetic markers of immunoglobulins (Ig) demonstrable by immunological methods have shown their usefulness as genetic probes. The study of these allotypes originally proved that Ig production is under conventional genetic control and also established that allelic exclusion is valid for the key molecules of the immune response. The codons responsible for the G1m(a) marker and their position in the human genome are precisely known. This knowledge implies that Gm typing may be used as a convenient and reliable means of following the fate of IgG constant gene segments. Anti-Gm's are common in rheumatoid arthritis. They appear early in the disease and may persist throughout life. The stimulus for their appearance has not yet been established. The anti-Gm's in the allegedly autoimmune disease rheumatoid arthritis are commonly and apparently paradoxically specific for Gm gene products of other persons. Another apparent paradox brought to light by Ig allotype research is the occasional appearance of non-nominal allotypes in contradiction to Mendelian laws. It is proposed that a plausible explanation for these two paradoxes is Ig gene transfer between individuals with viral vectors. Reasons for this proposal and some possible consequences of gene transfer in a polymorphic species are delineated. Immunogenetics and DNA technology in combination provide powerful tools to elucidate the fate of genes. A method allowing the assignment of G1m(a+) and G1m(a-) at the gene level by polymerase chain reaction analysis has recently been established and is briefly described.

Reaction of rheumatoid factors with IgG3 monoclonal anti-Rh(D) antibodies: more frequent reactivity to a monoclonal antibody of the Gm allotype G3m(5) in rheumatoid patients negative for G3m(5)

Human monoclonal anti-Rh(D) antibodies of known IgG isotype and Gm allotype were bound to erythrocytes and then used as the target IgG antigens for rheumatoid factors (RFs) in a direct haemagglutination test. When serum samples from patients with rheumatoid arthritis (RA) were tested for RF specificity towards these IgG monoclonal anti-D antibodies the incidence and titre of reactivity towards an IgG3 monoclonal anti-D antibody was considerably greater than for a polyclonal anti-D antibody of the same Gm allotype, G3m(5). This difference was not explained by the amount of each anti-D antibody which bound to erythrocytes. Furthermore, when patients with RA were divided into groups according to their Gm phenotype, sera from a greater proportion of patients negative for the phenotype G3m(5) reacted to the G3m(5) monoclonal anti-D antibodies than sera from those patients positive for this allotype. Analysis of RF reactivities towards two IgG3 and three IgG1 monoclonal anti-D antibodies, each with different Gm allotypic epitopes, indicated, however, that individual serum samples contained RFs with a spectrum of specificities; some sera appeared to react to a single set of Gm alleles, whereas others also reacted to isotypic or iso-allotypic epitopes, or both. Our data suggest that RFs with specificity for Gm allotypes do not arise in patients who carry that particular allotype owing to tolerance induced in fetal-neonatal life. Conversely, RFs with apparent specificity for a Gm allotype formed in patients negative for that allotype may be reacting to a closely related but different epitope. Final proof requires precise specificities for each RF formed, and IgG3 monoclonal anti-D antibodies would be useful reagents for this purpose.

IgG heavy chain (Gm) allotypes in rheumatoid arthritis and in healthy individuals seropositive for IgM-rheumatoid factor

The frequencies of Gm allotypes a, x, f, b, g and n have been investigated in classical seropositive rheumatoid arthritis (RA), erosive definite seronegative RA, non-erosive definite RA and in healthy individuals with serum IgM-RF. No differences in the frequencies of these Gm allotypes were found between patients and healthy controls. It is concluded that any possible putative genes outside the HLA region involved in RA are most likely unrelated to the genes coding for the constant regions of IgG heavy (gamma) chains.

Determination of human immunoglobulin M rheumatoid factor by a solid-phase radioimmunoassay which uses human immunoglobulin G in antigen-antibody complexes

A solid-phase radioimmunoassay for the rapid determination of human immunoglobulin M (IgM) rheumatoid factor (RF) has been developed. Preparation of the solid phase for the assay involved the formation of complexes between respiratory syncytial virus-specific human IgG antibodies and virus antigen on the surface of polystyrene balls. Binding of serum RF to IgG in the immune complex was subsequently detected by 125I-labeled mu-chain-specific antibodies to human IgM. The amount of radioactive indicator antibody bound was converted to units of RF by comparison to the standard curve for an RF reference-serum pool. This assay should prove useful in studies of the physiological role of RF, since it can effectively measure low levels of circulating RF.

Detection of IgG rheumatoid factor by concanavalin A treatment and complement fixation with IgG rheumatoid factor

Concanavalin A (Con A) froms precipitates with carbohydrate-rich protein such as IgM, IgD, IgE, and IgA. Since IgG contains little carbohydrate and does not react with Con A, the activity of IgG-rheumatoid factor (RF) can be measured in the supernate of the Con A-treated serum. When the latex fixation test (LFT) and the sensitized sheep cell agglutination test (SSCA) were perfromed in the supernate for the detection of IgG-RF, LFT was positive in 32-1% of sera, out of 137 sera originally positive for LFT, and SSCA was positive in 18-5% of sera, out of 119 sera originally positive for SSCA. IgG-RF exhibited lower complement fixing ability than IgM-RF and correlated with agglutination titres of IgG-RF, while the CH50 of the original serum did not correlate with haemolytic activities of either IgM-RF or IgG-RF.

The Gm and Inv factors in rheumatoid arthritis

The Gm(1), Gm(2), Gm(4), Gm(12), and Inv (1) factors were studied in the sera of 56 patients suffering from rheumatiod arthritis and 26 from various rheumatic diseases, by the hemagglutination inhibition test, using optimally reacting mixtures of Ragg and Nagg sera. The distribution of these factors was found to agree with that of healthy Greeks. No correlation was found between hypergammaglobulinemia and the discovery of the Gm(1) and Inv (1) factors. The presence of the rheumatoid factor was independent of the Gm and Inv phenotypes.