Catabolism and synovial transport of rheumatoid factor

Lessons from Carl M. Pearson 1919 - 1981

Carl M. Pearson was an energetic and exceptional physician-scholar-leader who founded, established, and broadened the Divisions of Rheumatology at University of California in Los Angeles (UCLA) beginning in 1956. His studies to induce myositis by injecting muscle saturated with the heat-killed tubercle bacillus, an emulsifier, and mineral oil (Freund's adjuvant) enabled his report that polyarthritis occurred with Freund's adjuvant alone in certain strains of rat and mice. This model of adjuvant arthritis allowed the next generation of studies to assess therapies for autoimmune diseases.

Elevated Membrane and Soluble CD64: A Novel Marker Reflecting Altered FcγR Function and Disease in Early Rheumatoid Arthritis That Can Be Regulated by Anti-Rheumatic Treatment

OBJECTIVES

Fc receptors (FcR) interacting with immune complexes (ICs) is a central event in the immune pathogenesis of rheumatoid arthritis (RA). Here we asked if a specific FcR is linked to RA pathogenesis and if FcR activities relate to disease and treatment outcome in early RA.

MATERIAL AND METHODS

Twenty autoantibody-positive RA patients and 33 HC were included. The patients were evaluated before and after treatment with methotrexate and prednisolone. At follow-up, the EULAR response criteria were applied to determine the individual treatment outcomes. Serum immunoglobulin levels were measured and the expression of FcR for IgG (FcγR) and IgA (FcαR) on peripheral blood monocytes were determined by flow cytometry. The monocytic FcγR function was evaluated by human IgG1 and IgG3 IC-binding and TNFα stimulated release. Plasma levels of soluble FcRs (sFcRs) were determined with ELISA.

RESULTS

The IgG1 and IgG3 levels were elevated in the RA sera. The RA monocytes expressed more CD64 and cell surface-bound IgG than HC monocytes, and showed an impaired FcγR function as reflected by changes in IC-binding and decreased IC-stimulated TNFα secretion. These findings correlated significantly with different disease activity markers. Furthermore, sFcRs were elevated in the patient plasma, and sCD64 was specific for RA (compared with a reference group of patients with active psoriatic arthritis). Following treatment, immunoglobulins and sFcR levels were reduced, whereas membrane CD64 was only decreased in patients with good response to treatment.

CONCLUSIONS

Early RA patients display increased membrane and soluble CD64 and an impaired FcγR function correlating with joint disease activity. Beneficial responses of anti-rheumatic treatment in patients reduce CD64. These data suggest sCD64 as an important objective biomarker in RA.

Absorption, distribution, metabolism, and excretion (ADME) studies of biotherapeutics for autoimmune and inflammatory conditions

Biotherapeutics are becoming an increasingly common drug class used to treat autoimmune and other inflammatory conditions. Optimization of absorption, distribution, metabolism, and excretion (ADME) profiles of biotherapeutics is crucial for clinical, as well as commercial, success of these drugs. This review focuses on the common questions and challenges in ADME optimization of biotherapeutics for inflammatory conditions. For these immunomodulatory and/or immunosuppressive biotherapeutics, special consideration should be given to the assessment of the interdependency of ADME profiles, pharmacokinetic/pharmacodynamic (PK/PD) relationships, and immunogenicity profiles across various preclinical species and humans, including the interdependencies both in biology and in assay readouts. The context of usage, such as dosing regimens, extent of disease, concomitant medications, and drug product characteristics may have a direct or indirect (via modulation of immunogenicity) impact on ADME profiles of biotherapeutics. Along these lines, emerging topics include assessments of preexisting reactivity to a biotherapeutic agent, impact of immunogenicity on tissue exposure, and analysis of penetration to normal versus inflamed tissues. Because of the above complexities and interdependences, it is essential to interpret PK, PD, and anti-drug antibody results in an integrated manner. In addition, because of the competitive landscape in autoimmune and inflammatory markets, many pioneering ADME-centric protein engineering and subsequent in vivo testing (such as optimization of novel modalities to extend serum and tissue exposures and to improve bioavailability) are being conducted with biotherapeutics in this therapeutic area. However, the ultimate challenge is demonstration of the clinical relevance (or lack thereof) of modified ADME and immunogenicity profiles.

Synovial synthesis of rheumatoid factors and immune complex constituents in early arthritis

Synovial synthesis of immune complex constituents and rheumatoid factors has been estimated in rheumatoid arthritis (RA) and in unclassifiable inflammatory arthritis (IA) and related to duration of symptoms. Within 6 months of onset of symptoms both RA and IA patients synthesised (or trapped) immune complexes locally. However, local synthesis of the rheumatoid factors was almost exclusive to RA patients and mainly in patients with symptoms of more than 6 months' duration. Thus all arthritis patients may respond immunologically to an initial trigger in the affected joint but only RA patients develop localised chronic autoimmunity later.

Immune complexes in early arthritis. II. Immune complex constituents are synthesized in the synovium before rheumatoid factors

Synovial fluids and paired sera taken from patients either before, after or at the time of diagnosis of definite rheumatoid arthritis (RA) were compared with samples from patients with unclassified inflammatory arthropathies (IA). Raised levels of immune complexes (IC) were detected in some RA patients by C1q binding activity but in the majority of both RA and IA patients by the platelet aggregation test; levels were usually higher in joint fluids than in sera. IgM rheumatoid factors (RF) and IgA RFs were lower in synovial fluids but IgF RF levels were similar in matched samples. Synovial fluid to serum albumin ratios were used to estimate synovial permeability (inflammation) and then to calculate which patients synthesized macromolecules locally in the synovium. Local synthesis of RFs was detected in a greater proportion of RA than IA patients and only two patients formed RFs locally in the first months of symptoms. Half the patients in both groups however appeared to synthesize or trap IC constituents and in many patients there was evidence of local synthesis within 6 months after their symptoms had started. We conclude that local synthesis of large amounts of RFs is uncommon in the early stages of RA but that IC of unknown composition are synthesized or localized in the affected joints of many patients with RA and inflammatory arthropathies shortly after their symptoms appear.

Inhibition of reticuloendothelial function by gold and its relation to postinjection reactions

A patient with rheumatoid arthritis developed severe exacerbation of symptoms 18 hours after an injection of gold thiomalate (sodium aurothiomalate). Immune complexes were present in his serum and synovial fluid; in the synovial fluid they were associated with intense complement activation. The effect of gold salts on splenic reticuloendothelial function was determined by measuring the clearance of heat-damaged erythrocytes from the circulation. Gold thiomalate (50 mg) substantially delayed clearance in the patient but had no effect in four other patients with rheumatoid arthritis who had not had a postinjection reaction. Severely impaired clearance also occurred in three out of four healthy people given 100 mg gold but they remained asymptomatic. The postinjection reaction may be an immune-complex disease that is triggered in certain patients because gold transiently inhibits reticuloendothelial function.

The primary plasmin inhibitor in rheumatoid synovial fluid

In 20 consecutive rheumatoid arthritis patients, 14 women and 6 men, age 26--76, average 62 years, the concentration of the recently found "primary plasmin inhibitor" and phase proteins was estimated in plasma and synovial fluid. In 12 patients a complex between the inhibitor and plasmin could be demonstrated by crossed immunoelectrophoresis into immunoglobulins against the primary plasmin inhibitor and immunoglobulin against plasminogen. Only free inhibitor was found in corresponding plasma. All plasminogen present in synovial fluid could be activated to plasmin upon addition of urokinase (24 nM/1). In those patients where enzyme-inhibitor complex in synovial fluid was present, a higher concentration of phase proteins in synovial fluid was found, indicating an increased degree of inflammation despite identical scores in the Lansbury clinical index in the two groups. From these experiments it was concluded that the fibrinolytic capacity in rheumatoid synovial fluid is not decreased. It is suggested that the fibrin-like material in synovial tissue and upon the synovial membrane is a poor substrate for plasmin.

Studies of cryoprecipitates from synovial fluid of rheumatoid patients

Sera and synovial fluids from thirty-seven patients with various types of arthropathy were studied for the presence of cryoprecipitates. The isolated, washed cryoprecipitates were analysed for immunoglobulins, antiglobulins, antinuclear antibody and DNA content. Cryoprecipitates were detected in the synovial fluids, but not in the matched serum specimens of twenty-six subjects, twenty-four of whom had rheumatoid arthritis. The precipitates consisted of either IgG—IgM complexes or IgG alone. Antiglobulin activity was present in the cryoprecipitates from nineteen rheumatoid patients; of these nineteen, fifteen had antiglobulins present in serum and fourteen had antiglobulins in their whole synovial fluids. Antinuclear antibody was detected in the cryoprecipitates from ten rheumatoid patients; only three patients had antinuclear antibodies in serum and/or whole synovial fluid. DNA was demonstrated in three cryoprecipitates and seven whole synovial fluids using an antiserum specific for calf thymus single strand DNA. When the cryoprecipitates were heat-denatured prior to testing, seventeen were shown to contain DNA antigens. The synovial fluids from one patient with Reiter's syndrome and one subject with psoriatic arthropathy also formed cryoprecipitates, but neither contained antiglobulin or antinuclear antibody activity. These observations suggest that the cryoprecipitates in rheumatoid synovial fluids contain several different antibodies and antigens, including antiglobulins, immunoglobulins, antinuclear antibody and DNA. It is postulated that these cryoprecipitates may represent cold insoluble antigen—antibody complexes.