A new protocol to digest human IgM with papain that results in homogeneous Fab preparations that can be routinely crystallized

A method has been developed for the routine production of Fab fragments from human IgM in high yield. After the IgM is purified at physiological pH, it is digested with papain in the presence of cysteine at room temperature for 16 hours. The Fab fragments are purified initially by gel filtration and then by ion exchange chromatography. The yield of Fab has been 60-80%. Some heterogeneity in the size of the Fabs from the different monoclonal IgMs has been observed. Fab fragments from four different IgM rheumatoid factors (RF) have been crystallized after such digestion and purification, in a variety of conditions including phosphate buffer alone or with the precipitating agents ammonium sulfate, polyethylene glycol or methylpentanediol. This modified papain digestion method has also been used for another non-RF monoclonal human IgM with equally good yield. Biological activity can be detected in the purified Fab fragment indicating that this procedure does not destroy the native conformation of the molecule.

[Immunology of the primary inflamed joint]

The primary inflammatory rheumatic joint has a high capacity to start a local autoimmune reaction. Prototype of this reaction is the rheumatoid joint. In this review evidence is provided that the rheumatoid joint exhibits--with a high degree of certainty--autoimmune reactions of both cellular and humoral autoimmunity against IgG, Collagen of various types, proteoglycans, nuclear antigens and C3b. It is also shown that such reactions are not restricted to rheumatoid joints and may be demonstrated in other joint diseases. The local chronic immune reaction may lead to cartilage destruction through four effector cells, that is macrophages, specialised fibroblasts, chondrocytes and neutrophils.

Relation between bone erosions and rheumatoid factor isotypes

Total rheumatoid factor (RF) activity and individual RF isotypes were measured in 62 patients with rheumatic diseases. Retrospective analysis of available x rays showed an association between IgA RF and the occurrence of periarticular bone erosions in hands. In contrast, IgG RF and IgM RF did not show any significant association with erosions. Furthermore, a close correlation was observed between the RF isotype levels in simultaneously drawn serum and synovial fluid samples. The possible significance of IgA RF in the pathogenesis of bone erosions is discussed.

Rheumatoid factor secretion from human Leu-1+ B cells

A human B cell subpopulation identifiable by the expression of the cell surface antigen Leu-1 (CD5) is responsible for most of the immunoglobulin M rheumatoid factor secreted in vitro after the cells are stimulated with Staphylococcus aureus. The ability of B cells bearing the Leu-1 marker (Leu-1+) to secrete rheumatoid factor is present early in development and extends to adulthood, since Leu-1+ B cells from cord blood and from peripheral blood lymphocytes of both normal adults and patients with certain autoimmune conditions secrete rheumatoid factor in comparable amounts. The neonatal enrichment of Leu-1+ B cells, the presence of Leu-1+ B cells in increased frequencies in patients with autoimmune disease, and the involvement of Leu-1+ B cells in autoantibody secretion suggest both developmental and functional homologies between this human B cell subpopulation and the murine Ly-1 B cell subpopulation.

7S IgM in the sera of patients with arthritis

Using radial immunodiffusion in 7% agarose, 7S IgM was quantified in the sera of 45 normal individuals, 37 patients with rheumatoid arthritis (RA), 18 patients with psoriatic arthritis and 11 patients with ankylosing spondylitis. 7S IgM was only found in the sera of patients with RA, 43% of whom had detectable levels of 7S IgM (median 47.5 micrograms/ml). The patients with 7S IgM had significantly higher IgM rheumatoid factor (IgM RF) and C-reactive protein levels in their sera (p less than 0.005). There was a strong correlation between 7S IgM and IgM RF levels in the sera of these patients. These data demonstrate that patients with more active and severe disease have 7S IgM present in their sera but the absence of 7S IgM from the sera of some patients with high levels of IgM RF and CRP suggest that additional factors may influence the synthesis and secretion of 7S IgM by B cells in RA.

[Cryoglobulins in arthritis]

During the years 1984-1986 we saw 22 patients with cryoglobulinemia, 8 of whom had rheumatoid arthritis, 1 psoriasis arthritis, 2 Sjögren syndrome, 1 progressive systemic sclerosis, 5 different arthralgias, 1 soft tissue rheumatism, 2 vasculitis and arthralgias and 2 purpura-arthralgia-nephritis syndrome. The measurement of cryoglobulins is done only in special cases of diagnostic importance. The prognostic outlook in patients with nephritis is bad. A monoclonal cryoglobulinemia is always suspicious for a lymphoproliferative syndrome.

T15 group A streptococcal Fc receptor binds to the same location on IgG as staphylococcal protein A and IgG rheumatoid factors

Previous work has shown that IgG rheumatoid factors (RF) bind to the C gamma 2-C gamma 3 interface region of human IgG in the same area that binds staphylococcal protein A (SPA). Group A, C, and G strains of Streptococci possess Fc receptors that bind to IgG but not to fragments containing only the C gamma 2 or C gamma 3 domains. This work describes the binding site location on human IgG for the binding of the isolated Fc receptor from the T15 strain of a Group A streptococcus and its relationship to the site that binds SPA and the IgG RF. The isolated T15 Fc receptor (T15) with a molecular mass of 29.5 kD inhibited the binding of IgG RF to IgG. The binding of T15 itself to IgG was strongly inhibited by SPA (42.0 kD) and its monovalent fragment D (7 kD). Human IgG fragments consisting of the C gamma 3 domains did not inhibit the binding of T15 to IgG, whereas those with both domains were effective inhibitors. T15 did not bind to rabbit IgG fragments consisting of either the C gamma 2 or C gamma 3 domains, but did bind to those with both domains. An IgG3 myeloma protein was a poor inhibitor and has been shown to bind poorly to the IgG RF. Most IgG3 myeloma proteins did not bind to SPA. The substitution of Arg and Phe for His 435 and Tyr 436 is responsible for the poor binding of IgG3 to SPA and to the IgG RF. Chemical modification of His or Tyr on IgG reduced its ability to inhibit the binding of T15 to IgG. Reversal of the chemical modifications with hydroxylamine resulted in near complete restoration of inhibitory capacity. This information, collectively, coupled with the known positions in space of the His and Tyr residues in the C gamma 2-C gamma 3 interface region, verified that both His 435 and Tyr 436, and possibly His 310 and 433, are involved. These residues are also involved in binding SPA and the IgG RF. These data therefore indicate that the T15 Group A Streptococcal Fc receptor binds to the same location on the Fc of IgG as SPA and the IgG RF. The biologic relevance of these similarities between bacterial cell wall Fc receptors and IgG RF are not yet apparent, but suggest that RF could bear the internal image of these bacterial structures.

Binding of monoclonal IgM rheumatoid factor to streptococci via the antibody combining site

Radiolabelled monoclonal IgM rheumatoid factors, four from patients with type II essential cryoglobulinaemia and one originating from a patient with rheumatoid arthritis, were tested for binding to group A, B, C and G streptococci and Escherichia coli. Two of the preparations exhibited different binding patterns for the streptococci, whereas the remaining three were not reactive. The binding of one of the factors to group A streptococci type 15 was inhibited by F(ab')2-fragments of anti-idiotypic antibodies but not anti-IgM Fc or F(ab')2 of normal rabbit IgG, indicating that the reaction was mediated via the antibody combining sites.

Relationships between non organ-specific autoantibody production and age-related modifications of mononuclear cell phenotype

13 autoantibodies were sought in 23-26 elderly people and in 47-118 young controls. We found at least one autoantibody (mainly rheumatoid factor, RF, and anti-nuclear antibodies in 17/23 elderly (i.e., 17%) and in 7/45 young controls (i.e., 16%). Autologous rosette-forming cells and Leu-7 positive cells (Natural Killer Cells?) were higher, and OKT4 and OKT8 positive cells lower in the former than in the latter group. We show that elderly have a high proportion of CD5 positive B cells, compared with young controls, following phorbol myristic acetate activation in vitro. This abnormality might account for the discrepancy in production of RF compared to other autoantibodies.

Circulating immune complexes in rheumatoid arthritis: a prospective study using five immunoassays

We evaluated 257 patients with rheumatoid arthritis (RA) to determine the frequency of circulating immune complexes (CIC) in the serum, relationships between the presence of CIC, clinical indices of disease activity and other laboratory features, and relationships between changes in CIC levels and changes in disease activity. CIC were detected by fluid phase Clq binding activity, conglutinin binding activity, anti-C3 assay, staphylococci protein A binding assay and the precipitation of cryoglobulins. CIC in the serum were found to correlate with indices of disease activity, extraarticular features and the presence of rheumatoid factor. A change in Clq binding activity correlated with a parallel change in the joint count.

Polymeric IgA rheumatoid factor in idiopathic IgA mesangial nephropathy (Berger's disease)

A specific and sensitive enzyme-linked immunosorbent assay (ELISA) was used to detect IgA rheumatoid factor (RF) in sera from 88 patients with IgA nephropathy (IgA GN), a disease characterized by abnormalities of IgA production. Significantly higher levels of IgA antiglobulins were demonstrated in IgA GN patients than in normal healthy controls and patients with other forms of chronic primary glomerulonephritis (mean +/- SEM 28.4 +/- 6.6 vs 6.0 +/- 0.4 and 8.3 +/- 1.2 micrograms/ml respectively; p less than 0.002). Interestingly, in contrast to rheumatoid arthritis, IgA RF activity was not associated with IgM antiglobulins. Analysis of sera fractionated by gel chromatography at acid pH revealed that anti-IgG activity resided predominantly in the polymeric fractions of IgA as confirmed by the ability to bind "free" secretory component. Several findings in patients with IgA GN suggest that the IgA deposited in the glomeruli is polymeric, and levels of circulating macromolecular IgA are increased. Our findings confirm a general perturbation of IgA metabolism in this disease. Although the polymeric nature of the IgA RF is suggestive of a mucosal origin, additional evidence is needed to confirm this hypothesis.

Pokeweed mitogen-induced secretion of IgG- and IgM-rheumatoid factors by synovial fluid and blood B lymphocytes in rheumatoid arthritis

Lymphocytes from patients with rheumatoid arthritis (RA) were assayed for their ability to secrete Ig and rheumatoid factors (RF) upon polyclonal activation in vitro. B lymphocytes secreting IgM-RF and IgG-RF were enumerated using hemolytic plaque forming cell (PFC) assays. The sensitivity of RF-PFC formation was similar to that of a reverse PFC assay detecting all cells secreting Ig. Blood mononuclear cells from RA patients generated a median of 12 IgM-RF and 15 IgG-RF-secreting cells/10(6) after 6 days culture with pokeweed mitogen (PWM). Thus a median of approximately 0.5% of IgM- and IgG-secreting cells were identified as RF-PFC. Synovial fluid B lymphocytes co-cultured with autologous blood T lymphocytes in the presence of PWM generated higher numbers of RF-secreting cells; medians of 43 IgM-RF and 441 IgG-RF secreting cells/10(6) were found. Thus, 8-9% of IgM- and IgG-secreting cells from synovial fluid were identified as RF-PFC. In co-cultures containing synovial fluid T cells, PWM-induced RF secretion was low. The data indicate that both blood and SF B cells have the potential for RF secretion.

Rheumatoid factor in rheumatoid arthritis associated renal disease and in lupus nephritis

To test the hypothesis that rheumatoid factor (RF) protects against (immune complex mediated) renal disease, patients with rheumatoid arthritis (RA; 48 with nephropathy of various types, 35 without renal disease) and systemic lupus erythematosus (SLE; 35 with and 17 without nephritis) were evaluated for the presence and titre of RF. There was no correlation between RF and nephropathy in RA, whereas in SLE RFs were almost exclusively seen in patients without nephropathy. This result supports the above hypothesis for lupus nephropathy but not for RA associated renal disease, and it may be explained by a more pronounced role for immune complexes in SLE and interference of RFs with the complexes.

Estimation of the relative avidity of 19S IgM rheumatoid factor secreted by rheumatoid synovial cells for human IgG subclasses

19S IgM rheumatoid factors (RF) may play an important role in sustaining inflammation in rheumatoid arthritis (RA). As yet, no unique antigenic specificity for RF in RA has been identified. Because the synovium is central to the pathogenic changes in RA, RF produced therein might be pathogenically more important than serum RF. Therefore, we examined the reactivity and relative avidity of 19S IgM-RF in serum and rheumatoid synovial cells (RSC) from 20 patients with seropositive RA. Reactivities were determined by competitive inhibition of serum RF hemolytic activity and RSC RF-plaque-forming cells (PFC) by added soluble antigen, i.e., monomeric human IgG subclasses. Estimation of relative avidities of RSC RF for human IgG subclasses was done by calculation of fractional RF expression in the RSC RF-PFC assay following inhibition by IgG subclasses. RSC RF had greatest reactivity with IgG3 and IgG1, some reactivity with IgG2, and the least reactivity with IgG4. Serum RF reacted most with IgG1 and IgG2, reacted some with IgG4, but reacted poorly with IgG3. The antigenic determinants with which RSC RF reacted were common to many IgG3 molecules. The highest relative avidity of RSC RF was for IgG3. These observations indicate a selective deficiency of serum RF compared with RSC RF and suggest an important pathogenic role for these qualitatively different RSC RF molecules for in situ RF immune complex-mediated inflammation in RA synovial tissue.

Inhibition of complement activation by IgG4 antibodies

Prolonged exposure to antigens may result in high IgG4 antibody titres as was shown in a previous paper (Aalberse et al., 1983b). In novice bee keepers, a shift in the IgG1/IgG4 ratio of the response against phospholipase-A (PLA; a major component of bee venom) occurred. This resulted in an IgG4-dominated response after approximately 2 years of bee-keeping experience. Subject of the present study was the influence of relatively high concentrations of IgG4 antibodies on the biological activity of immune complexes. In the PLA antigen model, it was demonstrated that IgG4-containing immune complexes do not activate complement and that IgG4 antibodies effectively inhibit immune precipitation and complement activation by IgG1 antibodies. Evidence is provided that IgG4 antibodies inhibit binding of C1q to IgG1 in mixed, IgG1- and IgG4-containing complexes. It is proposed that IgG4 antibodies protect against the biological effects of the complement-fixing IgG subclasses. For this reason, determination of the total IgG response or just determination of antibody activity in the complement-fixing isotypes is insufficient in immune-complex diseases. The modulating effect of the non-complement-fixing isotypes should be taken into account to predict the biological activity of the immune complexes.

Cryoprecipitation. In vitro studies on fibronectin as an independent cryoprecipitagogue

Fifteen patients affected by essential mixed cryoglobulinemia or secondary cryoglobulins were studied. Fibronectin was detected in the majority of essential mixed cryoglobulinemias, but in a minority of secondary cryoglobulins. In vitro studies gave strong evidence of an interaction between fibronectin and heat-aggregated gammaglobulins. The effects of fibronectin on cryoprecipitation of heat-aggregated gammaglobulins seem to support the independent role of the glycoprotein in the cryoformation mechanism, although its presence does not appear essential for cryoglobulin appearance.

Amino acid sequence of a light chain variable region of a human rheumatoid factor of the Wa idiotypic group, in part predicted by its reactivity with antipeptide antibodies

Antipeptide antisera were raised to the second and third complementarity-determining regions of the light chain derived from a human monoclonal IgM (Sie) which had antigammaglobulin activity and belonged to the Wa cross-reactive idiotypic group of human rheumatoid factors, two of whose members (Sie, Wo1) had been previously sequenced in our laboratory (Andrews and Capra, Biochemistry 20, 5816-5822, 1981). These antisera were found to react with the light chain of another human monoclonal IgM (Go1) that shared the Wa idiotype while antipeptide antisera made to the third CDR of the Sie heavy chain failed to react. The amino acid sequence of the variable region of the Go1 light chain was found to be highly homologous to the light chain of Sie from which the synthetic peptides were derived, particularly in the framework regions and the second and third CDR. This study illustrates that antipeptide antisera are valuable and specific probes for determining the relationship between molecules which exhibit similar antigen binding or idiotypic specificities and, furthermore, such antisera are able to predict amino acid sequences with surprising precision.

[Complement fragment C 3d in the plasma of patients with chronic polyarthritis]

Activation of the complement system via immune complex formation plays an important role in the perpetuation of chronic inflammatory disorders. The serum levels of C3 or C4 do not necessarily reflect the actual complement catabolism. By measurement of the long-lived C3 split product "C3d" direct information about complement activation can be obtained. C3d was measured with a modified immunoelectrophoresis technique in EDTA-plasma of 106 patients with rheumatoid arthritis. 36% of them showed significantly elevated C3d levels (mean: 8.93 micrograms/ml). Significant linear correlations were found for C3d with ESR, Lansbury-Index and plasma viscosity.

[Immunogenetic studies in patients with IgM rheumatoid factor negative erosive chronic polyarthritis (c.p.)]

40 patients with erosive rheumatoid arthritis (RA), 20 of whom were IgM-negative and 20 IgM-positive, were studied prospectively with regard to their association with HLA-B-CREGs (B5-, B8-, B12-, B16-, B27-CREG). We found a highly significant association of IgM-negative RA patients and B5-CREG-antigens (Chi2 = 28.6; p less than 0.001).

beta-Endorphin, immunological and biochemical changes in synovial fluid in rheumatic disorders

In 120 patients with rheumatic disorders concomitant assays of serum and synovial fluid were done for acute phase reactants, immunoglobulins and the neuropeptide beta-endorphin. One-third of the patients with rheumatoid disease demonstrated synovial fluid levels of endorphin to be several-fold higher than serum levels, while in two-thirds the opposite results were found. These changes are discussed as adaptive or defense mechanisms. The synovial membrane is postulated to synthesize beta-endorphin.

Effect of chronic ingestion of a prostaglandin E analogue on immunologic function in healthy elderly subjects

The immunologic effects of an oral prostaglandin E1 (PGE1) analogue were tested in 25 individuals over age 65, compared to 25 individuals given placebo. Elderly subjects were chosen because previous in vitro studies had found an increased sensitivity to PGE of lymphocytes in older subjects. After 2 weeks of ingestion of PGE analogue or placebo, there was a small but statistically significant decrease in IgM-rheumatoid factor in the PGE analogue group compared to control and a significant decrease in the in vitro sensitivity of lymphocytes from the PGE analogue group to inhibition by PGE. There were no differences in total lymphocyte count, T cell or T cell subset count, delayed hypersensitivity skin test reactivity, serum immunoglobulins, or response to mitogens between the two groups. Administration of an oral PGE analogue to normal elderly individuals is not associated with any detrimental effects on immunologic function after 2 weeks.

Binding of IgM rheumatoid factor to group A, C and G streptococci with IgG Fc receptors

The possibility that IgM rheumatoid factors bind to streptococci was studied. Using a sequence of Sephadex G200 gel filtration, protein A-Sepharose CL-4B chromatography and preparatory electrophoresis, IgM was isolated from the sera of 2 patients with rheumatoid arthritis and then radiolabelled with 125I. There was significant binding of radiolabelled IgM to group-A streptococci types M1, M15 and M22, and to a group-C and a group-G strain, all expressing IgG Fc receptors, but none to Staphylococcus aureus, Escherichia coli or to 11 other strains of streptococci without IgG Fc receptors. The radiolabelled IgM was separated by affinity chromatography on a column containing human IgG. Types M1 and M15 bound the fraction retained on the column, whereas M22 bound both this fraction and the non-retained fraction. Commercial human IgG, even at high concentrations, did not inhibit binding. The binding reaction, which is perhaps triggered either by the IgM rheumatoid factor or by IgG complexed with rheumatoid factor, could be a useful tool for removal of anti-immunoglobulin from the blood of patients with rheumatoid arthritis.