PROPERTIES OF VARIOUS ANTI-GAMMA-GLOBULIN FACTORS IN HUMAN SERA

IgG anti-hinge antibodies against IgG4 F(ab')2 fragments generated using pepsin are useful diagnostic markers for rheumatoid arthritis: implications of the possible roles of metalloproteinases and IgG subclasses in generating immunogenic hinge epitopes

Background

Pepsin agglutinators, discovered over 50 years ago, have been recently referred to as anti-hinge antibodies (AHAs) because of their reaction with the IgG hinge epitope. AHAs have different reactivity for each hinge epitope generated by each protease that cleaves the hinge region at different sites. Moreover, AHAs have different reactivity against different hinge epitopes derived from each IgG subclass even when the same protease is used. Since the expression of matrix metalloproteinase-3 (MMP-3) is enhanced in rheumatoid arthritis (RA), AHA production could also be increased. The purpose of this study was to determine whether the levels of AHAs against IgG hinge epitopes produced by MMP-3 are elevated in RA.

Methods

The serum levels of IgG or IgA AHAs against the IgG1/IgG4 F(ab’)₂ fragments, generated by either MMP-3 or pepsin, were measured using ELISA in 111 patients with RA and 81 healthy controls (HC). Receiver operating characteristic (ROC) analysis was used for obtaining optimal cutoff values and cutoff values indicating high specificity (> 95%) of the AHA. The targeted epitope of a specific AHA was investigated through inhibition ELISA.

Results

Seven AHAs were statistically higher in RA patients than in HC, except IgG AHA against IgG1 F(ab’)₂, which was generated by MMP-3 proteolytic cleavage. The areas under the ROC curve were 0.66–0.80, although the sensitivities at high specificity were low (5.4–24.3%). The cumulative number of positive AHAs in each individual was statistically higher in RA patients than in HC, suggesting the extreme extent of AHA repertoires in RA. Inhibition studies revealed that IgG AHAs against IgG4 F(ab’)₂ fragments generated by pepsin cross-reacted with IgG1 F(ab’)₂ fragments generated by pepsin. Multivariate logistic regression analysis identified the IgG AHA against IgG4 F(ab’)₂ fragments generated by pepsin as an independent variable for RA diagnosis, even in RA patients who were negative for both RF and ACPA (odds ratio 1.18, 95% CI 1.06–1.32; P = 0.003). Additional experiments using non-RA patients finally strengthened the diagnostic utility.

Conclusion

In RA patients, we observed diversification and amplification of AHA repertoires and diagnostic utility of the specific AHA against IgG4 F(ab’)₂ fragments generated by pepsin but not MMP-3.

Autoimmune disease etiology—a perplexing paradox or a turning leaf?

Autoimmune diseases such as rheumatoid arthritis, systemic lupus erythematosus, or scleroderma have been considered to represent disorders associated with reaction of the patient's own immune system against self-antigens or body systems. In many such disorders, tissues involved show lesions or morphology indicating destructive inflammatory or reactive features clearly produced by or associated with cell-mediated or antibody-driven reactions of the patient against his own tissues. After an exhaustive search which has stretched back in time for at least the last five decades, we seem to understand how the immune system works better than previously. However, despite the fact that we now understand molecular mechanisms of antibody selection and structure, how the cell-mediated and humoral antibody system is activated in terms of signal peptides and in the context of HLA molecules, we have not yet exactly identified inciting antigens which clearly cause these diseases. The focus recently has shifted towards being able to down-modulate potentially harmful parts of a self-directed inflammatory process by abrogating harmful messenger molecules participating in tissue injury. Following such a path, we may actually alleviate or cure these diseases before eventually identifying their original cause.

Autoantibodies as chameleons

Autoantibody determinations are frequently used by rheumatologists to establish the diagnosis or assess follow up clinical status in patients with connective tissue diseases. Such autoantibodies are often presumed to have harmful effects, particularly since some such as anti-native DNA or anti-Ro have frequently been related to tissue damage or to functional impairments. However, there are many other autoantibodies which react with antigenic components of normal autologous tissues which have not been demonstrated to have self-damaging or harmful effects. Some of these autoantibodies may actually represent natural built-in mechanisms of feed-back inhibition, serving to modulate normal physiologic function. Autoantibodies may be compared to chameleons since their function or quality is often judged by the company they keep or by their anatomical localization. Since many autoantibodies to intra-cellular products seem to react with active sites of important biologic molecules, they may provide us with a much sharper image of a number of natural cellular functions.

Characterization and V(H) sequences of human monoclonal anti-F(ab')(2) autoantibodies from normals and Sjögren's syndrome patients

To investigate the genetic background of anti-F(ab')(2) autoantibodies and the mechanism behind their production we have analyzed 10 human monoclonal antibodies directed against IgG F(ab')(2) and IgG Fab. They were all derived from peripheral blood by the EBV/hybridoma technique. Eight were from three healthy individuals and two from two patients with primary Sjögren's syndrome (pSS). They react with epitopes on distinct regions of IgG, including epitopes present on or near the hinge of IgG, epitopes on the Fd gamma, and an antigenic determinant(s) present on lambda light chains. These determinants are either exposed on the intact IgG molecule or revealed following pepsin or papain digestion. The V(H) germline gene repertoire used is diverse and with considerable overlap with that used by rheumatoid factors (RF). The two IgG antibodies from normals are extensively mutated (13 and 24 mutations/V(H)), but with a replacement to silent mutation ratio in the CDR(H)1 + 2 of only 3.7. The IgM antibodies from normals are also heavily mutated (mean 10 mutations/V(H)). This suggests that anti-F(ab')(2) from normals are generated by an antigen-driven somatic hypermutation mechanism. In contrast, the two IgM antibodies from pSS are virtually unmutated in both V(H) and V(L). Together with published data of pSS RF and anti-Ro 52-kDa sequences (1-3), this suggests that there is an expanded population of naïve B cells with autoantibody specificities in the peripheral blood of pSS patients.

Cross-reactivity of human IgG anti-F(ab')2 antibody with DNA and other nuclear antigens

OBJECTIVE

To characterize immunologic specificity and possible antiidiotype activity of IgG anti-F(ab')2 in normal subjects as well as in patients with active and inactive systemic lupus erythematosus (SLE).

METHODS

IgG anti-F(ab')2 and anti-double-stranded DNA (anti-dsDNA) were affinity isolated from immunoadsorption columns of F(ab')2 and dsDNA linked to Sepharose 4B. Affinity-purified IgG anti-F(ab')2 (APAF) and affinity-isolated IgG anti-dsDNA (APAD) were tested by enzyme-linked immunosorbent assay (ELISA) for other cross-reacting specificities including anti-Sm, anti-Sm/RNP, and anti- Crithidia binding. Anti-DNA specificity of APAF and APAD was assayed by S1 nuclease treatment of heat-denatured DNA. Rabbit antiidiotypic antisera were prepared by immunization with APAF and APAD from normal subjects and SLE patients and absorption with insolubilized human Cohn fraction II (Fr II). VL and VH regions of 5 monoclonal IgM antibodies with anti-F(ab')2/anti-DNA specificity generated by Epstein-Barr virus B cell stimulation were sequenced by polymerase chain reaction and characterized for VH and VL subgroup. APAF and APAD were also examined by high-resolution electron microscopy for possible ring forms indicative of antiidiotypic V-region interactions.

RESULTS

APAF from normal subjects, representing 0.08-0.18% of serum IgG, showed striking relative concentrations of both anti-F(ab')2 and anti-DNA, as well as anti-Sm and anti-Sm/RNP ELISA reactivity. Both APAF and APAD reacting with F(ab')2 or dsDNA on the ELISA plate could be cross-inhibited by F(ab')2 or DNA in solution. Anti-DNA reactivity in normal APAF and APAD was much more sensitive to S1 nuclease treatment than similar fractions from SLE patients. Neither APAF nor APAD from controls produced positive antinuclear immunofluorescence or positive Crithidia staining, whereas these were strongly positive using SLE APAF and APAD. Absorbed rabbit antisera against normal or SLE APAF and APAD showed strong ELISA reactivity against both APAF and APAD, but no residual reactivity with normal Fr II. VL and VH sequencing of monoclonal human IgM antibodies showing both anti-F(ab')2 and anti-DNA reactivity showed relative VH3, V kappa 1 or VH1, V kappa 3 restriction. No evidence of ring forms or V-region "kissing" dimers was obtained when normal or SLE APAD or APAF was examined by high-resolution electron microscopy.

CONCLUSION

IgG anti-F(ab')2 in both normal subjects and SLE patients represents a polyreactive Ig subfraction with concomitant anti-DNA, anti-Sm, and anti-Sm/RNP specificities. Anti-DNA reactivity in SLE is qualitatively different from that in normal APAD and APAF since normal APAD and APAF anti-DNA is much more sensitive to S1 nuclease digestion of denatured dsDNA. APAF and APAD share distinct V-region antigens which may be related to prominent VH3 or VH1 antigenic components. No evidence for in vivo complexing of anti-DNA and anti-F(ab')2 as ring forms or antiidiotype-IgG complexes was observed during ultrastructural studies. In both normal individuals and SLE patients, APAF may represent a small polyreactive IgG subfraction which also contains antinuclear and anti-DNA specificities.

Anti-IgG autoantibodies and possible immune regulatory mechanisms in patients with pulmonary tuberculosis

SETTING

Anti-Ig antibodies are known to have important clinical and biological implications.

OBJECTIVES

To determine naturally occurring anti-F(ab')2 gamma and anti-Fc gamma antibodies in patients with pulmonary tuberculosis (PTB) in relation to various clinical manifestations and human leukocyte antigen (HLA).

DESIGN

Antibodies to F(ab')2 and Fc portions of IgG were detected in the sera of normal healthy individuals (n = 41), patients with pulmonary tuberculosis (n = 50) and their household family contacts (n = 20) using an enzyme immuno assay (EIA) system.

RESULTS

As compared to controls (0.110 +/- 0.01 optical density [OD]), the levels of anti-F(ab')2 gamma were significantly increased in PTB patients (0.998 +/- 0.08 OD, P < 0.0001) and in their contacts (0.486 +/- 0.04 OD, P < 0.001) suggesting that the occurrence of these autoantibodies is related to infection/exposure to Mycobacterium tuberculosis. Anti-F(ab')2 gamma antibodies were significantly increased in both sputum positive and negative patients (P < 0.0001) and no deviation was observed between these two groups. The levels of these antibodies were positively correlated with disease severity assessed by chest X-ray. The drug failure patients had higher activity of anti-F(ab')2 gamma than drug responders and no impact of anti-tuberculosis chemotherapy was observed. A statistically significant increase of anti-F(ab')2 gamma levels (1.25 +/- 0.21 OD) was observed in HLA-DR2 positive patients as compared to the DR2 negative groups (1.02 +/- 0.09 OD), P < 0.01. No deviation was observed in the levels of anti-Fc gamma levels between controls and any group of PTB patients.

CONCLUSION

The present data suggests that the elevated levels of anti-F(ab')2 gamma antibodies in PTB patients represent an anti-idiotypic antibody response to anti-M. tuberculosis antibody caused by an immune imbalance following M. tuberculosis infection.

Anti-gammaglobulin factors in human sera revealed by enzymatic splitting of anti-Rh antibodies. Vox Sang 1963;8:133-52

Human sera were found that contained antibody activity which caused agglutination of red cells or particles sensitized with immunoglobulin G that had first been degraded by pepsin proteolysis. The agglutinating activity was specific for a determinant that was not present on the untreated, native immunoglobulin. It was found most frequently in sera from rheumatoid arthritis patients and its titre showed some correlation with disease activity.

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.

Human anti-F(ab')2 antibodies show preferential reactivity for F(ab')2 molecules bearing lambda light chains

In order to evaluate binding specificities of anti-F(ab')2 antibodies from patients with systemic lupus erythematosus (SLE) and from normal healthy controls, F(ab')2 fragments were prepared from 24 IgG myelomas with defined isoelectric points, DNA-associated idiotypes, and kappa/lambda light chain types. Using ELISA and hemagglutination assays, anti-F(ab')2 antibodies from 12 healthy controls and 29 SLE patients were observed to exhibit preferential binding (lambda > kappa) to myeloma F(ab')2 fragments composed of lambda light chains (P < 0.0001). No correlation of anti-F(ab')2 binding and presence of cationic, neutral, or anionic isoelectric points or for DNA-associated idiotypes on monoclonal F(ab')2 was detected. Anti-F(ab')2 antibodies, often elevated in SLE during remission, show preferential specificity for F(ab')2 fragments bearing lambda light chains.

Parallelism of serum anti-F(ab')2 and anti-cationic IgG reactivities in patients with systemic lupus erythematosus

Cationic anti-DNA antibodies may be related to glomerular injury in murine lupus nephritis or in patients with systemic lupus erythematosus (SLE). Therefore, anti-cationic antibodies in SLE could include antibodies with regulatory function on such pathogenic cationic molecules. Since anti-F(ab')2 antibodies may be involved in the idiotype control of anti-DNA antibodies in some patients with inactive SLE, the present study was aimed to determine if SLE patients with significant serum levels of anti-F(ab')2 produce antibodies reacting with cationic IgG molecules. Three SLE sera with high titers of anti-F(ab')2 antibodies were individually adsorbed by sequential affinity chromatography on three Sepharose columns coupling normal IgG from Cohn Fraction II, pooled cationic IgG myeloma paraproteins displaying idiotypic anti-DNA markers (F4 and 8.12), and F(ab')2 fragment from allogeneic IgG, respectively. Eluates obtained from cationic IgG adsorption showed predominant anti-F(ab')2 reactivity. A similar profile was also detected in a serum from a normal control donor with high levels of anti-F(ab')2. Biotinylation of anti-cationic eluates showed that such antibodies were significantly more reactive with cationic than anionic or neutral IgG, confirming their apparent affinity for positively charged antigens on IgG molecules. Since anti-cationic absorptions were able to remove the anti-F(ab')2 activities in the SLE sera studied, it is possible that anti-cationic antibodies could function as immunoregulatory antibodies in the idiotypic control of some SLE autoreactive phenomena, including glomerular anti-DNA deposition.

The specificity of antiglobulin autoantibodies in patients with primary Sjögren's syndrome

Antiglobulin autoantibodies have already been demonstrated in the sera of patients with primary Sjögren's syndrome (primary SS). In our study, the specificity of primary SS antiglobulins for different regions of IgG molecules was examined by employing both direct binding and competitive inhibition enzyme-linked immunosorbent assay. We found that a considerable amount of total antiglobulins in primary SS was specific for the Fab portion, although the remainder was specific for the Fc portion, namely rheumatoid factor (RF). In contrast, most of the antiglobulins in RA were specific for the Fc portion of IgG. These results indicate that in primary SS, antiglobulins directed against epitopes different from those of RF are produced. These antiglobulins may prove to have a different role in primary SS than that ascribed to RF in RA.

Enzyme immunoassay detection of circulating immune complexes by monoclonal antibodies to C3 neoepitopes with special reference to IgG concentration and to interfering anti-immunoglobulin antibodies

A sensitive solid-phase anti-C3 enzyme immunoassay for detection of circulating immune complexes (CIC) is described. A mixture of the monoclonal antibodies (MoAbs) bH6 and Clone 9 specific for neoepitopes on C3 activation products was used as capture reagent. MoAb bH6 recognized C3b, iC3b and C3c, and Clone 9 recognized iC3b and C3dg. Detection antibody was a polyclonal peroxidase-conjugated rabbit anti-human Ig antiserum. A quantitative assay was constructed using serum incubated with heat aggregated IgG (HAG) as standard. The lower detection limit was 5 micrograms/ml of HAG. Interassay and intra-assay coefficient of variation was 15% and 5%, respectively. Anti-animal immunoglobulin antibodies were detected both in normal and pathological sera. This activity was efficiently absorbed by nonimmune immunoglobulins added to the samples. The present assay was compared with a polyethylene glycol precipitation assay for CIC determination. The latter assay was strongly influenced by the IgG concentration (rs = 0.78; P = 0.006), whereas no such correlation was seen for the anti-C3 immune complex assay (rs = -0.30; P = 0.20).

Anti-F(ab')2 antibodies in thrombocytopenic patients at risk for acquired immunodeficiency syndrome

22 homosexual or narcotic addict patients at risk for acquired immunodeficiency syndrome (AIDS) or with AIDS, were studied for the presence of antiimmunoglobulin antibodies and circulating immune complexes (20 were thrombocytopenic, 6 had AIDS). Circulating immune complex levels were 10-fold higher than levels in normal subjects. IgG anti-F(ab')2 antibodies were noted in homosexual as well as narcotic addict patients. Of 16 homosexual patients, 7 had IgG anti-F(ab')2 antibody of moderate to marked titer with broad reactivity against autologous, homologous, and control F(ab')2 fragments. Three others demonstrated limited reactivity against one or two F(ab')2 fragments. The remaining six patients were negative. Six of six narcotic addict patients had IgG anti-F(ab')2 antibody, five with limited reactivity, one with broad reactivity. In contrast, neither elevated circulating immune complexes nor anti-F(ab')2 antibodies were detectable in six autoimmune thrombocytopenic patients. Anti-F(ab')2 antibody could be affinity purified from serum or circulating immune complexes. Anti-F(ab')2 reactivity correlated with circulating immune complex levels, r = 0.83, P less than 0.01.

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.

Family distribution of anti-F(ab')2 antibodies in relatives of patients with systemic lupus erythematosus

Recently we reported an inverse relationship between the levels of anti-F(ab')2 antibodies and disease activity in systemic lupus erythematosus (SLE). The present study focused on anti-F(ab')2 antibodies in unaffected relatives of SLE patients. Sixty sera from first degree family members from 11 SLE families and 49 sera from 8 control families were studied. Percentage of SLE family members with anti-DNA antibodies (15%) was higher than than control family sera (8%, P less than 0.05). Anti-F(ab')2 antibodies were measured using ELISA assays. The SLE family sera had higher amounts of anti-F(ab')2 antibodies than the normal control family group (P = 0.0051). In an effort to determine if anti-F(ab')2 antibodies found in high titres in the sera of some SLE family members had specificity for the F(ab')2 fragment of anti-DNA antibodies of the SLE relative patients, DNA-anti-DNA inhibition experiments were performed using anti-F(ab')2 prepared from the relative in parallel with anti-F(ab')2 prepared from normal controls with equivalent high titres of serum anti-F(ab')2. Inhibition exhibited by anti-F(ab')2 of first degree relatives was higher than that obtained from control normal donors (P less than 0.02). Such differences in inhibition were not recorded using a control tetanus toxoid-anti-tetanus toxoid assay. In direct binding ELISA experiments, peroxidase-conjugated anti-F(ab')2 antibodies from the same first degree relative showed high relative specificity against purified anti-DNA antibodies of his SLE proband when compared to those obtained against different anti-DNA antibodies isolated from unrelated SLE patients (P less than 0.001). Such a substantial difference was not observed in parallel experiments using peroxidase conjugated anti-F(ab')2 antibodies from normal controls unrelated to SLE subjects.

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.

Reactivity of sized thermal aggregates of immunoglobulin G with IgM rheumatoid factor

Solutions of purified pooled human IgG heated for varying times and temperatures between 55 degrees and 65 degrees yielded soluble turbid non-immune polydispersed aggregate mixtures. Gel filtration of IgG aggregate mixtures on calibrated Biorad A-15, A-50 or A-150 columns resulted in continuous size distributions from dimers to particles with mol. wts. as high as 5 X 10(7) (300-mers) with no particular size predominant. Chromatographically reproducible cuts of relatively narrow size heterogeneity were obtained by 15 min time fractionation. The reactivity of sized aggregates was studied with pooled purified IgM rheumatoid factor as well as with various individual IgM RF sera. The inhibition of agglutination method employing IgG-coated tanned sheep cells was used to assay relative reactivities. With all RF preparations studied, reactivity of sized IgG was primarily a function of aggregate size. Reactivity increased from virtually zero with monomeric IgG to maximal values with aggregates in the 10(6) size range. Larger aggregates (mol. wt. 10(7) or greater) exhibited diminishing and ultimately negligible reactivity. Reactivity of aggregates of given size was independent of heating time but increased with decrease in heating temperature. The maximal reactivity of certain sizes of IgG aggregates with RF suggests that at least two factors are operative. Enhanced reactivity may be due to unblocking of potential reactive sites on IgG during denaturation that precedes aggregation or to the more favourable energetics of binding with aggregates as compared to monomer. Subsequent loss of reactivity may be due to steric hindrance in large aggregates and/or to destruction of binding sites as a result of continued denaturation.

Characterization of anti-Fab' antibodies in human sera: identification of soluble immune complexes that contain hidden anti-KLH and blocking anti-immunoglobulins following immunization with keyhole limpet haemocyanin

After immunization with keyhole limpet haemocyanin (KLH), increased concentrations of anti-KLH and anti-Fab' antibodies (Abs) were demonstrated in sera from 18 of 20 volunteers. In many cases, post-immunization sera contained soluble immune complexes that incorporated both anti-Fab' and 'hidden' or 'blocked' anti-KLH antibodies. The complexes containing hidden anti-KLH and blocking anti-Fab' Abs were not found in pre-immunization sera. The hidden Abs to KLH were revealed by demonstrating increases in anti-KLH activity in sera incubated previously with Fab' fragments, immobilized on plastic microtitre tray wells. Incubation with insoluble Fab' did not influence the quantity of anti-tetanus toxoid (TT) that was detected in these sera. Addition of affinity purified anti-Fab' Abs to samples, previously 'unblocked' by adsorption with immobilized Fab', depressed their anti-KLH activity to levels present before adsorption, but did not change the quantity of Abs to Dermatophytin, Trychophyton, or TT therein. These results suggest that some autoantibodies generically recognized as 'Fab' specific' have properties that are usually considered to be characteristic of autoanti-idiotypes.

IgM and IgG anti-F(ab')2 antibodies in rheumatoid arthritis and systemic lupus erythematosus

Radioimmunoassays for anti-F(ab')2 antibodies, which feature the use of goat anti-human Fc antibody for correcting potentiation of IgM anti-F(ab')2 antibody titers by endogenous IgM anti-Fc antibodies (rheumatoid factors), are described. Individuals with classic rheumatoid arthritis had significantly more IgM anti-F(ab')2 antibody (P less than 0.001) and IgG anti-F(ab')2 antibody (P = 0.05) than did individuals with systemic lupus erythematosus or normal volunteers. There is some similarity in patterns of isotype distribution of anti-F(ab')2 antibodies and rheumatoid factors.

Peripheral T lymphocytes from rheumatoid arthritis patients recognize determinants on light chains and/or Fab fragments of immunoglobulin G

Peripheral blood T lymphocytes from 29 of 31 patients with rheumatoid arthritis incorporated significant quantities of thymidine when cultured with pooled human immunoglobulin G (IgG). In contrast to the observation of general reactivity to pooled Igg, responses to pooled IgM were rare (3 of 26 patients). None of 11 controls responded to either IgG or IgM. Response to IgG is maximal on day 6 of culture and is dependent on concentration of IgG. The responding cells recognize determinants on monoclonal light chains and/or Fab fragments. Response to light chains follows one of three patterns: preferential response to lambda chains, preferential response to kappa chains, and essentially equal response to either kappa of lambda chains.

Cytotoxicity of anti-Fab antibodies against B lymphocytes in rheumatoid arthritis

Anti-Fab antibody titers were positive in 70% of rheumatoid arthritis patients (54 of 77) and 3% (1 of 35) of healthy donors. Their specificity was examined by inhibition of the radioimmunoassay for anti-Fab antibodies, which demonstrated that they are against the Fd region of the intact immunoglobulin molecule. In addition, anti-Fab antibodies have broad specificities for IgG antigens, shown by inhibition with myeloma IgG. They are cytotoxic against B (20% of B cells from most healthy donors) but not T lymphocytes, with cytotoxicity greater at 5 degrees C than 37 degrees C. These studies show that the anti-Fab antibodies interact with allotypic or idiotypic determinants on subpopulations of B lymphocyte cell surface antigens.

Naturally occurring human antibodies to the F(ab')2 portion of IgG

Antibodies to the F(ab')2 portion of IgG were detected in the sera of patients and normals using a heat-aggregated F(ab')2 fragment in a liquid-phase radioimmunoassay. The antibodies were found in 72% of 82 rheumatoid arthritis patients, in less than 20% of patients with other diseases and in a few normal subjects. Anti-F(ab')2 antibodies were distinct from previously described anti-Fc antibodies and 'serum agglutinators'. They reacted with intact IgG, F(ab')2 and IgM in binding and inhibition assays and they appeared to have specificity for the Fd portion of IgG molecules, possibly to the VH region. The anti-F(ab')2 antibodies were of both 7S IgG and 19S IgM classes and were found in sera as components of intermediate size (between 7S and 19S) and large size (greater than 19S) immune complexes. The possible contribution of autologous anti-F(ab')2 to abnormal immunoregulation is discussed.

Interactions between IgM antiglobulins and IgG antinuclear antibodies. Some aspects of D-penicillamine activities

In this report we describe an in vitro masking action of IgM rheumatoid factor (IgM-RF) towards IgG antinuclear antibodies (IgG-ANA) which can be recovered by using D-penicillamine (DP) as an unmasking agent. The mechanism of this masking effect was elucidated by using smears of rat free nucleus as substrate, instead of the classical rat liver cryostat sections technique. It was postulated that the 'inhibition' of IgG-ANA by IgM-RF may be due to the formation of high molecular weight complexes (HMWC); this would be the same in vivo. Allowing the formation of HMWC which can be removed from the circulation, IgM-RF may have a protective effect by preventing or minimizing systemic lesions. Therefore, IgM-RF may be considered as a defence response against potentially noxious ANA or antigen-antibody complexes. Induced nephropathy and the high frequency of detection of ANA observed in rheumatoid arthritis (RA) patients treated by DP may be the result of the dissociating effect of this drug on HMWC, in which the activity of pre-existing ANA is hidden when rat liver sections are used for its detection.

Granulocytic function after administration of pepsin treated human gammaglobulin

Pepsin-treated human gammaglobulin, 150 mg/kg body weight, was administered intravenously to 14 healthy volunteers. Before and after the infusion the nitroblue tetrazolium (NBT)-reduction of granulocytes was studied in all and the bactericidial capacity in 12 subjects. An increase of NBT reduction (p less than 0.05) and of bacterial capacity (p less than 0.01) of granulocytes was found after the infusion. The effects may be due to an opsonising action of F (ab')2 components.

Further studies of the adjuvant properties of homologous IgG split products: mode of action of F(ab')2 and related fragments

Peptic bivalent and monovalent Fab' fragments as well as F(ab')2 fragment from a purified rabbit anti-DNP antibody were equally effective in enhancement of the immune response to SRBC. In contrast, the papain Fab fragment of normal IgG possessed a considerably lower enhancing activity. These data indicate that the effector site(s) controlling the adjuvant activity of F(ab')2 and related fragments is structurally distinct from the antibody active site(s) within the fragment molecule, and is located in C-terminal region of the heavy chain Fd fragment. When F(ab')2 fragment was injected into rabbits together with the proteinase inhibitor Trasylol it failed to enhance the immune response to SRBC. Furthermore, Trasylol interferes with the ability of F(ab')2 or Fab' fragment to activate the complement system both in vivo and in vitro. This, together with the observation that F(ab')2 fragments enhance the response to T-dependent antigens (SRBC and bovine gamma globulin) but fail to augment the response to LPS, suggests that these fragments may operate via activation of complement and thereby influence indirectly the reactivity of complement receptor B cells.

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.

Cathepsin D agglutinators in rheumatoid arthritis. I. Increased CDA titers in serum and synovial fluid of patients with seropositive RA

The incidence and titer of cathepsin D agglutinators (CDA) were significantly higher in seropositive rheumatoid arthritis (RA) sera than in the sera of healthy blood donors or of patients with other rheumatic diseases, including seronegative RA. A significant elevation was also found in synovial fluid (SF) samples from seropositive RA patients. CDA in the SF tended to be increased when compared with the corresponding serum. The levels of CDA correlated positively with those of rheumatoid factors (RF) when the latter were determined with IgG anti-CD Ripley-coated erythrocytes, but not when they were determined by the Waaler-Rose or latex tests. The increased CDA titers do not seem to be the result of significant amounts of IgM agglutinators or of the presence of IgM-RF. These findings suggest the existence of a link between the formation of RF and CDA, but the nature of this link cannot be fully explained.

Inhibition of spontaneous and antibody-dependent cellular cytotoxicity by sera and isolated antiglobulin preparations from rheumatoid arthritis patients

Using sera from patients with rheumatoid arthritis and antiglobulin preparations obtained from such sera, inhibition of human lymphocyte cytotoxicity in antibody-dependent (ADCC) and spontaneous cell-mediated cytotoxicity (SCMC) reactions against an allogeneic melanoma cell line (IGR3) has been demonstrated. Fractionation of effector cell preparations indicated that Fc-receptor-bearing lymphocytes were operative in both reactions. Removal of phagocytic and adherent cells from the effector cell population resulted in more pronounced inhibition of SCMC and ADCC reactions by rheumatoid sera. The results indicate that antiglobulin preparations from human sera containing rheumatoid factor activity can effectively block the cytotoxic activity of Fc-receptor-bearing effector lymphocytes (K cells) in vitro. On analogy with the inhibition of ADCC and SCMC reactions by immune complexes and aggregated IgG, antiglobulin complexes present in the antiglobulin preparations are responsible for this effect.

IgG heavy chain sub-classes in mixed cryoglobulins

IgG heavy chain sub-classes were assayed in thirteen mixed cryoglobulins. In eight the distribution of sub-classes in the cryoglobulin was different from that in the serum. In two the IgG component of the cryoglobulin consisted entirely of IgG3. A restricted distribution of heavy chain sub-classes in mixed cryoglobulins probably reflects the heavy chain specificities of the antiglobulin components.

Human serum antibodies specific for secretory IgA

Human antibodies which react in a haemagglutination system with secretory IgA, but not serum IgA, were found in serum from 14 per cent of normal subjects, 8 per cent of patients with chronic inflammatory bowel diseases and over 50 per cent of subjects with either peptic ulcer or alcoholic cirrhosis. The specificity of these reactions for secretory IgA was confirmed in inhibition experiments using a panel of immunoglobulin proteins. The anti-secretory piece factors in two sera were found by zone electrophoresis and sucrose density gradient experiments to have physical characteristics most compatible with IgG and IgA proteins, respectively. Further characterization of the specificity of these anti-secretory IgA factors, using a panel of colostral IgA proteins from individual mothers and isolated secretory piece, demonstrated a high degree of variability in antigenic specificity for secretory IgA. In three of five sera tested, the reaction was specific for components in isolated secretory piece. Inhibition studies using products of peptic digestion of colostral IgA suggest that secretory piece is attached to the Fc fragment of the molecule and that digestion releases at least some secretory piece molecules relatively intact. Although the significance of these anti-secretory IgA antibodies is presently unknown, it is anticipated that they will be valuable as reagents in further studies on the molecular structure and biology of secretory IgA.

Humoral responses in human organ transplantation

The plasmas of fifteen patients undergoing organ transplantation were serially tested for a variety of humoral antibodies. The antibodies studied were those which usually reflect covert immunologic events, i.e. the antiglobulins (rheumatoid factors and serum agglutinators), heterophile antibodies and typical and atypical isoantibodies.

Although the isoantibodies and the heterophile antibodies were not significantly stimulated by organ transplantation, the administration of ALG (horse antilymphocyte globulin) invariably led to the presence of antihorse globulin antibodies. Three patients were Rh negative and received organs from Rh-positive donors. However, only one of the patients responded with anti-Rh antibodies, but these antibodies exceeded in titre the anti-Rh antibodies usually observed following intentional immunization of normal volunteers.

The most startling observation was the significant increase in titres of the serum agglutinators in eight of the patients. These observations suggest that the antigen–antibody complexes associated with chronic rejection may stimulate the production of the serum agglutinators.