Immune complexes and complement catabolism in ankylosing spondylitis

Relation of microscopic haematuria in ankylosing spondylitis to circulating IgA containing immune complexes

Ankylosing spondylitis (AS) is associated with IgA nephropathy. To study the pathogenetic mechanism of this association the presence of haematuria and circulating IgA containing immune complexes (IgA ICs) in 70 patients with AS was determined. In this retrospective study haematuria was present in 15 patients and 25 patients had IgA ICs. Circulating IgA ICs were shown in 9/15 (60%) of the patients with haematuria and in 16/55 (29%) of those without haematuria. These results suggest that IgA ICs in patients with ankylosing spondylitis have a pathogenetic role in causing IgA nephropathy.

Absence of IgA nephropathy in patients with ankylosing spondylitis

In 40 patients with ankylosing spondylitis (AS) no evidence for IgA nephropathy was obtained. This conclusion was based on the absence of hematuria and on the inability to find an increased incidence of IgA-containing immunoglobulin deposits in skin biopsies. Increased Clq binding assay was only found in those AS patients with anterior uveitis. In 26% of the skin biopsies perivascular mononuclear cell infiltrates were observed, and immunoglobulin deposits were seen in 65%. These facts suggest that the immunologic system is involved in the pathogenesis of this disease.

Immunology of multisystem ocular disease

In this review based on Prof. James' 1983 George Nelms Wise Lecture, the authors summarize proven and speculated relationships involved in the immunology of multisystem ocular disease. Extensive tables elucidate the mechanisms underlying such conditions as, systemic lupus erythematosus, polyarteritis nodosa, Sjögren's syndrome, Wegener's granulomatosis, scleritis, sarcoidosis, Behcet's disease, idiopathic retinal vasculitis, sympathetic ophthalmia, Vogt-Koyanagi-Harada syndrome, and dysthyroid eye disease.

The in-vivo metabolism of C3 in ankylosing spondylitis

Turnover studies with radioactively labelled C3 were performed in 7 patients with ankylosing spondylitis and in 14 healthy individuals . As a group the patients had a moderately higher fractional catabolic rate of C3 than the controls. A possible explanation is that the complement system is activated by immune complexes. The serum levels of C3 were high. The hypercatabolism was therefore more than compensated for by an increased synthesis rate.

The absence of circulating immune complexes in patients with ankylosing spondylitis

Sera from 50 patients with well-defined ankylosing spondylitis were examined for circulating immune complexes using both a Clq binding (fluid phase) assay and a Raji cell assay. No more than five of the patients assessed had circulating immune complexes by either one of these techniques and none were positive in both. This result is in contrast to the high prevalence in sera from unselected patients with rheumatoid arthritis and systemic lupus used as positive controls.

Circulating immune complexes in patients with ankylosing spondylitis

EDTA plasma samples from 13 patients with ankylosing spondylitis (AS) were fractionated on Sephadex G-200 and the quantities of C3 and IgG within the first protein peak determined by a sensitive haemagglutination-inhibition assay. Seven patients with AS had G3 detectable in the first peak and this was associated with an increased concentration of IgG in the corresponding fraction. These 7 patients had more active disease but did not have more peripheral arthritis. Our results indicate that circulating immune complexes capable of initiating complement activation are present in the circulation of patients with ankylosing spondylitis.

Failure to find C1q-binding material and anti-IgG antibodies in ankylosing spondylitis

C1q-binding immune complexes (C1C), anti-IgG antibodies (anti-IgG Ab), and complement levels were investigated in the serum of 37 patients with ankylosing spondylitis (AS). In all these studies the mean levels observed in patients with AS were similar to those in 31 normal subjects. Moreover, no significative difference in either CIC or anti-IgG Ab levels was observed when the patients were classified in different clinical forms according to the localisation (peripheral and central) or to the gravity (mild and severe) of the AS. In a parallel study increased CIC and anti-IgG Ab levels were found in most of the 81 patients with seropositive or seronegative rheumatoid arthritis.

Soluble immune complexes in human disease

The great variety in biochemical properties of immune complexes occurring in human and animal disease states has made the detection of such complexes a difficult task. Variability in immune complex size, specificity, and interaction with humoral or cellular receptor systems, such as complement and phagocytes, suggests different pathogenic properties. The introduction of radioimmunoassays and the recently improved knowledge of the immune complex-receptor interactions have lead to the description of a large number of detection procedures, which in turn has widened the catalogue of diseases associated with immune complexes. This widespread occurrence of soluble immune complexes has lead many investigators to think that such complexes may occur either as a transient physiological phenomenon, important for fast clearance of the antigen, or as primary pathogenic factors triggering inflammatory reactions. Among the 50 procedures for immune complex detection known today, the article will select some pertinent tests, which will be discussed with respect to their specificity, sensitivity, and reproducibility. Furthermore, it is well known that when applied to the study of a patient group with one particular immune complex disease, various tests will result in different percentages of patients having complexes. This observation is due to differences in the underlying principle on which the various tests are based. Thus immune complexes must be further characterized with respect to their size, to the antibody class or specificity involved and, most difficult, to the antigenic specificity which participates in the complex. Recent advances in such experimental characterization of immune complexes in vitro and in the clinical evaluation of patients with complement activation associated to the presence of immune complexes will be discussed.