Capacity to solubilize immune complexes in sera and synovial fluids from patients with rheumatoid arthritis

Characterisation of the size and composition of circulating immune complexes in patients with rheumatoid arthritis

The size and composition of circulating immune complexes in the sera of patients with rheumatoid arthritis (RA) were studied in relation to different manifestations of the disease. Circulating immune complexes from the sera of 94 patients (50 with extra-articular disease) and 10 matched controls were fractionated by sucrose density gradient ultracentrifugation. The composition, immunoglobulin and rheumatoid factor (RF) concentrations within each of the fractions were determined by a sensitive enzyme linked immunosorbent assay (ELISA). Intermediate size (14S-21S) IgG complexes containing RF activity and 22S IgG-IgM RF complexes were found in the sera of 40 patients with RA, while intermediate size complexes of self associated IgG RF and larger size complexes (greater than 22S) of IgG RF and IgM RF were associated with extra-articular features of RA (50% of extra-articular disease). Complexes containing IgA were found in the sera of many patients with RA, and dimeric IgA RF mainly in patients with extra-articular disease. These results support the view that whereas small size circulating immune complexes are of no primary pathogenic importance in synovitis, large size (greater than 22S) circulating immune complexes may play a role in extra-articular disease in RA. Current understanding of the formation of large complexes provides a biological explanation for their occurrence and effects.

Immune-complex vasculitis: role of complement and IgG-Fc receptor functions

Vasculitis contributes a major component to the pathogenesis of rheumatic diseases and glomerulonephritis. A common feature of these diseases is the presence of serum immune complexes (IC) which may be deposited in blood vessel walls. The modification of the size and solubility of IC by the classical and alternative complement pathways, and the recent demonstration of the role of cellular complement receptors and IgG-Fc receptors in the handling of IC, now allow a better understanding of the pathogenesis of the severe forms of vasculitis. When complement deficiencies are present, the handling of IC is impaired, and vasculitis results. New blood tests for Factor VIII-related antigen, alkaline ribonuclease, plasma thrombospondin, and anti-neutrophil cytoplasmic antibody correlate with the presence of selected types of vasculitis. In addition, tissue thromboplastin release after application of defined tourniquet pressure can also detect subtle blood vessel injury. These new tests may allow diagnosis without risky organ biopsies. Advances in the diagnosis and treatment of vasculitis will also be discussed.

The role of polymeric IgA in complement-mediated solubilization of IgG and IgA immune complexes

Sera from patients with IgA nephropathy (IgAN) have a reduced capacity to solubilize immune complexes. The in vitro complement-mediated solubilization of immune complexes containing IgG (bovine serum albumin [BSA]-anti-BSA) or IgA (DNP29-BSA-anti-DNP) was decreased, despite normal serum levels of complement. The close correlation between low values for complement-mediated solubilization and high serum levels of polymeric IgA and/or IgA rheumatoid factor indicates that these macromolecules interfere with the process. These findings suggest that polymeric IgA produced during stimulation of mucosae specifically interferes with immune complex solubilization. Further studies are necessary to elucidate the mechanisms. The decreased complement-mediated solubilization in patients with IgAN could be responsible for persistently high levels of immune complexes containing IgA or IgG in the circulation and their continual deposition in the mesangium.

Circadian and diurnal variation of circulating immune complexes, complement-mediated solubilization, and the complement split product C3d in rheumatoid arthritis

Nine patients with active classical rheumatoid arthritis (ARA criteria) were studied with reference to circadian variation of immunological and clinical parameters. Complement-mediated solubilization (CMS) of immune complexes (IC) and the level of circulating IC were found to be inversely related with low CMS and increased IC levels in the morning, and vice versa in the afternoon. Bed rest and exercise did not influence these fluctuations. The C3d concentration in plasma was increased but showed no diurnal or circadian periodic fluctuations when the levels were corrected for fluctuations in plasma albumin concentration. Clinical assessment by means of pain score exhibited marked variations, with high scores in the morning, and lower in the daytime, whereas measurements of Ritchie's joint index showed no consistent pattern. The circadian variations in CMS, serum IC and clinical parameters indicate the need to collect blood specimens and perform clinical examinations of patients at a fixed time of day.

Inhibitory effect of IgM rheumatoid factor on immune complex solubilization capacity and inhibition of immune precipitation

Purified IgM rheumatoid factors (RF; 3 monoclonal and 2 polyclonal) were shown to inhibit, in a dose-dependent manner, 2 complement-mediated functions, i.e., the immune complex solubilization capacity and the inhibition of immune precipitation. Inhibition of immune complex solubilization capacity occurred only if RF was added at the same time as, but not after, addition of the complement source. Experimental evidence suggests that the effects of RFs were not related to their anticomplementary activity, but rather required the attachment of RF to the Fc region of the IgG molecule. Although no clinical data are available so far, it might be plausible that these newly described properties of RF have biologic relevance.