Studies of human anti-gamma-globulin factors reacting with pepsin-digested gamma-globulins

Immunomodulatory potential of anti-idiotypic antibodies for the treatment of autoimmune diseases

The immune system is a complex network of specialized cells and organs that recognises and reacts against foreign pathogens while remaining unresponsive to host tissues. This ability to self-tolerate is known as immunological tolerance. Autoimmune disease occurs when the immune system fails to differentiate between self and non-self antigens and releases autoantibodies to attack our own cells. Anti-idiotypic (anti-ID) antibodies are important in maintaining a balanced idiotypic regulatory network by neutralising and inhibiting the secretion of autoantibodies. Recently, anti-ID antibodies have been advanced as an alternative form of immunotherapy as they can specifically target autoantibodies, cause less toxicity and side effects, and could provide long-lasting immunity. This review article discusses the immunomodulatory potential of anti-ID antibodies for the treatment of autoimmune diseases.

The immune system protects the body against infections and diseases, such as by producing antibodies. Usually, these antibodies only attack pathogens, leaving healthy cells unharmed. However, autoimmune disease may develop when the immune system mistakenly recognises part of the body as foreign and produces antibodies to attack them. Antibodies that attack our own cells are called autoantibodies. Anti-idiotypic antibodies could be utilized to stop autoantibodies from attacking self cells with minimal side effects and long-lasting immunity. This review discusses anti-idiotypic antibodies usage as an alternative form of immunotherapy to inhibit autoantibodies in autoimmune disease.

Human anti-F(ab')2 antibodies and pepsin agglutinators react with Fv determinants

Affinity-purified human IgG anti-tetanus antibody was subjected to papain and then pepsin digestion, and residual fragments retaining antibody activity were re-isolated by adsorption and elution from Sepharose-tetanus toxoid columns. Both Fab' and Fv fragments isolated by gel filtration showed strong reactivity with anti-F(ab')2 antibodies. Failure of tetanus toxoid to completely block reactivity of anti-F(ab')2 antibody with anti-tetanus Fv fragments indicates that these antibodies react with framework antigens within variable antibody regions.

The specificity of antibodies to the F(ab')2 fragment of human IgG

The specificity of IgG anti-F(ab')2 antibodies was examined by unfractionated sera of patients with rheumatoid arthritis and also with affinity-purified antibody preparations. Examination of the sera by an enzyme-linked immunosorbent assay, using pooled human F(ab')2 fragments absorbed to microtiter plates, revealed that IgG anti-F(ab')2 antibodies cross-react with human and rabbit IgG and rabbit F(ab')2. IgG anti-F(ab')2 antibodies were purified by affinity chromatography and, when tested by a fluid-phase inhibition enzyme-linked immunosorbent assay, were found to be of 2 types. One fraction, similar to pepsin agglutinator, reacted with human F(ab')2 fragment alone. The other fraction was cross-reactive with human IgG and yet failed to react with idiotopes on Fab or epitopes on Fc fragments. The IgG anti-F(ab')2 antibodies we purified had no reactivity toward a human immune complex prepared from tetanus toxoid and antitoxoid.

Specificity of IgM antibodies to pooled human F(ab')2 fragments

An isotope specific immunoassay which minimizes interference by endogenous rheumatoid factors was used to determine the specificity of IgM anti-F(ab')2 antibodies in human serum. We underscore the heterogeneity of these antibodies. While one subset of IgM anti-F(ab')2 antibodies reacts only with intact F(ab')2, another recognizes determinants present following reduction and alkylation of F(ab')2 and separation of Fd' fragments from light chains. IgM anti-F(ab')2 antibodies in sera from rheumatoid arthritis patients do not react significantly with intact pooled IgG and, therefore, probably are not anti-idiotypic antibodies. Some sera, but not all, contain elevated levels of antibodies that are crossreactive with rabbit F(ab')2. Such crossreactive antibodies may interfere with assays which utilize F(ab')2 fragments of rabbit antibodies specific for antigens of clinical relevance.

Particle counting immunoassay. IV. The use of F(ab')2 fragments and N epsilon-chloroacetyl lysine N-carboxyanhydride for their coupling to polystyrene latex particles

Improved performance with the latex agglutination immunoassay, PACIA, is possible when the F(ab')2 fragments of antibody are chemically coupled at their hinge region to a protein-coated latex using a new coupling reagent, N epsilon-chloroacetyl lysine N-carboxyanhydride. This reagent, whether by orientating the complete antibody molecule or its F(ab')2 fragment or by preventing antibody denaturation, increased the sensitivity of the PACIA method. The use of F(ab')2 fragments eliminated most serum interference with the test.

Cathepsin D agglutinators and neutral protease agglutinators in rheumatoid arthritis. II. Production of CDA and NPA by rheumatoid synovium and phagocytosis of CDA by synovial phagocytic cells

Tissue culture methods demonstrated the production of agglutinators against the cathepsin D site in IgG (CDA) and a neutral protease site in IgG (NPA) by rheumatoid synovial tissue. Seven of 11 specimens from seropositive and 2 of 7 specimens from seronegative RA patients were positive for CDA, whereas 2 of 11 specimens from seropositive and 1 of 7 specimens from seronegative patients were positive for NPA. None of the 6 control specimens was positive for both types of agglutinators. Chromatography of two synovial tissue incubates showed that the CDA were of the IgG type. By the immunofluorescence technique, plasma cells containing CDA were demonstrated in rheumatoid synovial tissue and draining lymph nodes of rheumatoid joints. The staining for CDA in the synovium was different from the staining for pepsin agglutinators in adjacent sections. Phagolysosomes containing CDA were found in synovial exudate cells from rheumatoid patients as well as in phagocytosing lining cells and macrophages of the sublining layer of rheumatoid synovial tissue. These findings suggest that antibodies directed at hidden antigenic sites in IgG revealed by endogenous proteolysis take part in the immune reaction and in the inflammation of rheumatoid joints.

Naturally occurring antiglobulin factors in virus neutralization: homoreactant as a factor enhancing neutralization of the infectious complex of poliovirus with the Fab' antibody fragment

A factor present in normal rabbit sera enhanced the neutralization of the infectious complex of poliovirus with the pepsin Fab' fragment of rabbit immunoglobulin G (IgG) antibody but showed no activity for the infectious complex of the same virus with IgG antibody. The factor was associated with IgG, and its activity was inhibited by the pepsin Fab' fragment of normal rabbit IgG. The data suggest that the enhancing factor belongs to naturally occurring antiglobulin to the homologous Fab' fragment (pepsin homoreactant).

Immune responses to the cleavage-associated neoantigens of fibrinogen in man. Identification and characterization of humoral antibodies specific for cleavage fragments

Cleavage of human fibrinogen and fibrin by plasmin is associated with modification of native antigenic expression and the exposure of cleavage-associated neoantigenic sites on the derivative molecular fragments. In this study, the presence of humoral antibodies in man to cleavage-associated neoantigens has been demonstrated by primary antigen binding radioimmunochemical assays. Specific binding of radioiodinated human fibrinogen D fragment by serum immunoglobulins was demonstrated in 52 of 59 random normal human sera and was independent of immunoglobulin concentration. Binding was mediated by F (ab)2 fragments of IgG, and specificity for neoantigens was indicated by the capacity of the D fragment but not native fibrinogen to competitively inhibit the antibody. The population distribution of antibody to these cleavage-associated neoantigens indicated the presence of a major group of individuals (77%) with a mean antigen binding capacity of 11.8 pmol/ml serum. Two minor populations with : (a) low or undetectable binding capacities (less than 6.0 pmol/ml serum) and (b) exhibiting markedly elevated binding capacities (less 18.0 pmol/ml serum) were delineated. Independent of these features, sera could also be readily separated into two groups that differed with respect to relative antibody affinity. The antibodies in most sera exhibited marked heterogeneity of binding affinity, whereas a small group of sera contained antibodies exhibiting relative homogeneity of binding affinity. Specific antibody was rather equally distributed between the major immunoglobulin classes, and in no serum was the antibody restricted to a single immunoglobulin class. Antibodies capable of binding fibrinogen fragments X, Y, and D and fibrin D fragment were detected in most sera. The quantity of antibody differed for different fragments with X greater than Y congruent to D greater than fibrin D. The presence of antibody capable of binding any single fragment was statistically correlated with the presence of antibody capable of binding other cleavage fragments. No antibody to the E fragment was detected. Antibody to cleavage fragments was not demonstrable in sera containing fibrinogen or fibrin cleavage fragments. Demonstration of this humoral immune response to the products of the fibrinolytic systems provides a new interface between the coagulation and immune system.

Antibodies to human albumin in cirrhotic sera

In a previous paper we described a monoclonal IgM protein with antibody-like activity towards aggregated and native albumin. The present study was initiated to determine whether sera, other than that from patients with macroglobulinemia, contained similar antibody-like activity. It was demonstrated that approximately 40% of the sera from patients with classical Laennec's cirrhosis contained antibodies which agglutinate sheep red blood cells coated with aggregated albumin. The hemagglutinating activity was present in the void volume on Sephadex G-200 chromatography and was shown to be an immunoglobulin by its removal on passage over an anti-L-chain immunoadsorbent column. The immunoglobulin was isolated from cirrhotic sera by chromatography on an albumin immunoadsorbent column. The acid eluate from the albumin affinity column contained only IgA. After labeling this IgA with (125)I and obtaining the Fabalpha fragment by proteolysis, it was shown that the labeled Fabalpha complexed noncovalently with aggregated albumin. Complex formation between albumin and the cirrhotic IgA and Fabalpha could also be demonstrated utilizing facilitation of hemagglutination of sheep red blood cells coated with aggregated albumin. Appropriate controls consisting of normal and myeloma IgA and myeloma Fabalpha fragments failed to show evidence of complex formation with albumin. We propose that the restriction of the antibody response to the IgA class may result from the formation of antibodies against albumin altered during metabolism in the gastrointestinal tract. A possible role for anti-albumin antibodies in normal albumin catabolism and in the pathogenesis of Laennec's cirhosis is discussed.

IgG hydrolysis in abscesses. I. A study of the IgG in human abscess fluid

Human abscess fluids have been shown to contain Fc and Fab fragments of IgG. The Fab fragments were able to inhibit chymotrypsin and subtilisin agglutinators but not pepsin, papain, ficin, bromelin, or trypsin agglutinators. The levels of proteolytic enzymes in abscess fluids were measured and shown to be high.

A monoclonal IgM protein with antibody-like activity for human albumin

The serum of a patient (L'ec) with an IgM lambda monoclonal protein was noted to bind albumin on immunoelectrophoresis. Analytical ultracentrifugation of the L'ec serum demonstrated 23S and 12S peaks, but no 4S (albumin) boundary. Immunologically identical 20S and 9S IgM proteins were isolated from the serum and the addition in vitro of either the patient's albumin or albumin isolated from normal serum was shown to reconstitute the 23S and 12S boundaries. The binding of high molecular weight IgM to albumin was demonstated by Sephadex G200 chromatography with (125)I-labeled albumin and isolated IgM. Immunoelectrophoresis of the L'ec IgM developed with aggregated albumin (reverse immunoelectrophoresis) also demonstrated the binding of albumin to IgM. That all of the patient's IgM complexed with albumin was shown by affinity chromatography employing an aggregated albumin-immunoadsorbent column. Binding was shown to be of the noncovalent type by polyacrylamide gel electrophoresis in 8 M urea. With hot trypsin proteolysis, Fabmu and Fcmu5 fragments were isolated, and monomer albumin was shown to complex only with the Fabmu fragment by both analytical ultracentrifugation and molecular sieve chromatogaphy employing (125)I-labeled Fab fragments. 1 mol of Fabmu fragment bound 1 mol of monomer albumin. Polymers of human albumin, produced by heat aggregation, precipitated with the isolated L'ec protein on gel diffusion analysis and, when coated on sheep red blood cells, gave a hemagglutination titer greater than 1 million with the whole L'ec serum. 50 additional monoclonal IgM, 33 IgA, and 80 IgG sera failed to show precipitation or hemagglutination with aggregated albumin. Native monomer albumin inhibited precipitation only at high concentrations (> 50 mg/ml); dimer albumin or fragments of albumin produced by trypsin digestion inhibited at low concentrations (0.4 mg/ml). No reactivity occurred with the albumin of five other mammalian species, including bovine. The L'ec protein has the characteristics of an antibody against aggregated albumin, which also has reactivity with native (monomer) albumin. This system shares many similarities with the reaction of IgM human rheumatoid factors with IgG antigen.

Molecular events responsible for modulation of neoantigenic expression: the cleavage-associated neoantigen of fibrinogen (blood coagulation-fibrinogen cleavage products-fibrinolysis-molecular conformation)

Molecular events responsible for modulation of neoantigenic expressions of a defined molecule have been explored in relation to three hypothetical molecular models (see below). Fibrinogen and its cleavage-associated neoantigen have been used as a prototype system. Physicochemical and enzymatic factors influencing neoantigenic expression were evaluated. The cleavage-associated neoantigen was not only exposed by plasmin and enzymes of similar specificity, but also in a qualitatively and quantitatively deficient fashion by enzymes of differing specificities. Denaturation of fibrinogen via reduction or pH alteration did not induce the neoantigen, but oxidation of the native fibrinogen molecule did elicit this neoantigenic expression. The neoantigen, once exposed on the D-fragment, was relatively stable to physical and chemical denaturation. These results are inconsistent with proposed cleavage site specific and neoconformational determinant models and are consistent with a steric model, which postulates that the cleavage-associated neoantigenic determinant is buried in native fibrinogen but is exposed in certain altered molecular species. The importance of molecular conformation in the exposure of antigenic expressions of a molecule and in modulation of the binding affinity of a neoantigen for specific antibody is demonstrated.

Serum agglutinators in families with twins

This study of serum agglutinator titres in twins shows that the titres of these anti-Fab antibodies are apparently influenced by (unknown) stimuli in the environment and the influence of heredity should be relegated to the potential to produce IgG globulins in general.

Evidence for immune complexes containing antibody to the pepsin site of IgG in rheumatoid synovial fluids

In seventy cases of rheumatoid arthritis, the synovial fluid to serum ratio for the titre of pepsin agglutinator, i.e. the antibody to the pepsin site of IgG, was studied. This was compared with the corresponding ratio for another antibody of the same immunoglobulin class and for other proteins. By this method there was evidence for local production of pepsin agglutinator in two cases and for local inhibition in two other cases. Density gradient ultracentrifugation, performed at pH 7·4 and 3·0, suggested that pepsin agglutinator in immune complexes was present in most of the synovial fluids containing this antibody. Complexes of pepsin agglutinator and F(ab')₂ IgG, prepared in vitro, appeared to fix only small amounts of human complement. Neither did fixation of pepsin agglutinator to immune precipitates increase their complement binding activity.

Anti-globulin antibodies detecting hidden gamma G antigens: characterization of the "pepsin site" by different immune antisera

The antigenic region of human γG-globulin revealed by pepsin digestion has been studied by means of four different `pepsin agglutinator' (PA) containing sera. Two of these were `naturally occurring' agglutinators found in human and subhuman (baboon) sera respectively. The other two were heteroimmune antisera produced by the immunization of rabbits with human and baboon F(ab′)₂ fragments. All of the PAs were agglutinating but not precipitating.

Each PA reacted specifically with γG₁ and γG₃ immunoglobulins as determined by testing with isolated human myeloma proteins. One of the rabbit PAs (RAHPA) reacted with both reduced and unreduced pepsin fragments in contrast to the other agglutinators. In addition, different reaction patterns were evident when the PAs were tested with a panel of pepsin digested primate γG-globulins.

The general trend of the data suggested that a similar antigen was being detected by the four PAs. Further, it was evident that a limited degree of heterogeneity existed within the human `pepsin site' and between similar regions in higher primates.

Human anti-gamma-globulin antibodies specific for gamma G heavy chain subclasses

Anti-γ-globulin antibodies which show specificity for γG₁ and γG₃ subclass antigens respectively have been detected in human sera. In contrast to most of the subclass antigens which are present in intact γ-globulin, these antigens are only revealed by pepsin digestion. This is the first test system employing human anti-γ-globulin antibodies for determining γG subclasses of isolated antibodies and myeloma proteins. These anti-γ-globulins also react strongly with autologous pepsin-digested γG-globulin. The finding of human anti-γ-globulin antibodies with these fine specificities for γG subclasses and autologous γG-globulin suggests that their function is closely related to certain specific-γG antibody populations.

The findings show that both γG₃ and γG₁ molecules have subclass specific antigenic structures which are revealed following pepsin digestion.

Naturally occurring pepsin agglutinators in the serum of subhuman primates

Antibodies directed against both human and infrahuman pepsin digested γ-globulin were present in a majority of the primate sera tested. The subhuman pepsin agglutinators paralleled previously described human pepsin agglutinators in respect to their wide distribution in normal sera, their specificity and cross-reactivity, and their immunochemical features. The pepsin agglutinators† at different primate levels appeared closely related.

Among the subhuman pepsin agglutinators a subspecificity was described for a subhuman primate antigen. This finding suggested some limited differences between the subhuman pepsin agglutinators and the human pepsin agglutinators.

Experimental immunization of four cynomologous monkeys failed to elicit or alter these serum reactants.

Immunologic enhancement of tumor xenografts by pepsin-degraded immunoglobulin

The serums from guinea pigs previously injected with mouse Ehrlich ascites tumor cells were fractionated to obtain gamma(2)-immunoglobulin. This immunoglobulin was degraded with pepsin to obtain an F(ab')(2) fragment. Fresh tumor cells were incubated with immunoglobulin or the fragment and injected into normal guinea pigs. The growth of these cells as tumor xenografts was inhibited by the gamma(2)-immunoglobulin and enhanced by the F(ab')(2) fragment. Similar incubation of tumor cells with normal guinea pig gamma(2)-globulin or its derived F(ab')(2) fragment did not alter subsequent tumor growth.

The relationship between rheumatoid factors and serum agglutinators

A detailed study of the DEAE fractionated serum R. W. [anti-Gm(x)] has revealed differences in specificity between the 7S serum agglutinators of erythrocytes sensitized with anti-Rh antibodies digested with proteolytic enzymes and 19S rheumatoid factor monospecific for Gm(x). The serological reactivity and specificity of the serum agglutinators is determined by the enzymatic modification of the globulin molecules and is unrelated to the Gm type. On the other hand, the 19S rheumatoid factor [anti-Gm(x)] is reactive with undigested molecules or with those antibody molecules digested with proteolytic enzymes which leave the Fc piece intact. The 19S factor specificity is otherwise unrelated to digestion of the globulin molecule and rests solely on the intactness of the Gm site for which it is specific.