Complement-activating properties of immune complexes are suppressed by IgM rheumatoid factor and enhanced by IgG rheumatoid factor

The lupus patient with positive rheumatoid factor

Background Patients with systemic lupus erythematosus (SLE) may form clusters with clinical manifestations and autoantibodies. Objective The objective of this report is to study whether SLE patients with positive rheumatoid factor (RF) have a special clinical and/or serological profile. Methods A retrospective study of 467 SLE patients seen at a single rheumatology unit was conducted. Epidemiological data (age, gender, age at disease onset, ethnic background and tobacco use), clinical data (malar rash, photosensitivity, oral ulcers, discoid lesions, serositis, glomerulonephritis, convulsions, psychosis, hemolytic anemia, leukopenia, lymphocytopenia, arthritis and hypothyroidism) and serological profile (anti-dsDNA, anti-Ro/SS-A, anti-La/SS-B, anti-RNP, anti-Sm, IgG aCL, IgM aCL, lupus anticoagulant, direct Coombs and RF) were collected. Patients with positive and negative RF were compared. Results RF was found in 24.9% of the sample. In univariate analysis, RF was positively associated with butterfly rash ( p = 0.04), anti-Ro ( p = 0.03), anti-Sm antibodies ( p = 0.01) and hypothyroidism ( p = 0.01) and negatively associated with glomerulonephritis ( p = 0.003). Logistic regression showed that only glomerulonephritis ( p = 0.03; OR = 0.45; 95% CI = 0.21-0.93) and anti-Ro ( p = 0.009; OR = 2.3; 95% CI = 1.24-4.57) were independent associations. Conclusion In our sample RF was associated with protection from glomerulonephritis and with higher prevalence of anti-Ro antibodies.

The stimulation of Toll-like receptors by nuclear antigens: a link between apoptosis and autoimmunity

As immunologists have long understood, effective responses to foreign antigens require adjuvants. It is now apparent that the initiation of autoimmune disease is comparably facilitated by adjuvant activity. In the case of antinuclear antibodies, it seems that DNA itself can serve as an endogenous adjuvant. Similar to many of the microbial adjuvants, mammalian DNA mediates its effect through a Toll-like receptor--in this case, TLR9.

Modulation of antigen-antibody complexations by immunoglobulins

In this investigation, the modulating effects of non-immune human IgG and rheumatoid factors (RFs) on antigen-antibody complexations were studied. Non-immune human IgG, as well as RF, were found to inhibit the binding of antigen to specific antibodies of both human and rabbit origin. In addition, human immunoglobulins were also able to modify the composition of preformed antigen-antibody complexes. The effects were detected by immunological methods in two different antigen-antibody systems (human serum albumin-rabbit anti-HSA and tetanus toxoid-human anti-TT). Changes in biological activities could be followed by employing enzymes (glucose-6-phosphate dehydrogenase and human placental alkaline phosphatase) as antigens. The outcome of the effects was found to be dependent on the ratio of antigen to antibody, the antigen-binding properties of the antibody and its origin, and on the properties of the immunoglobulins added. The observed changes could not be explained only by the presence of specific antibodies in the immunoglobulin preparations. The ability of immunoglobulins to modulate antigen-antibody complexations may provide a rationale for the large amounts of non-specific immunoglobulins in the circulation by preventing premature precipitation and promoting the elimination of antigenic molecules.

Rheumatoid factors

Rheumatoid factors (RFs) have been studied for over 50 years and are probably the most written about of any antibody. Nevertheless, the etiology of these RFs and the precise role they play in the pathogenesis of rheumatoid arthritis (RA) and juvenile rheumatoid arthritis (JRA) remain a major interest. When RFs participate in the generation of inflammation in RA and JRA, they probably do so by forming immune complexes (IC) or are themselves able to bring about the inflammatory response. Their presence has been associated with more severe disease, vasculitis, and systemic symptoms. The present review summarises the literature over the last few years on new and interesting findings on RF. This review covers an update on RF assays, RF cross-reactivity, specificity studies, immune complex formation, RF lymphocyte studies, and RF binding.

Possible role of microbial IgG Fc-binding proteins in rheumatoid arthritis

IgG Fc binding substances (receptors) are widespread among pathogenic microorganisms. The receptors from Staphylococcus aureus, streptococci of group A, C and G as well as Herpes-infected cells bind to the interface between the CH2 and CH3 domains i.e. to His 435, Tyr 436 and possibly also His 433 and/or 310. Most rheumatoid factors (RF) from patients with rheumatoid arthritis show a similar binding pattern. Hence, it has been shown that antibodies to microbial IgG Fc receptors (S. aureus and group A streptococci type M15) and RF are idiotypic-anti-idiotypic antibody "partners" i.e. that RF are the "internal images" of microbial IgG Fc binding proteins. Group A streptococci possessing IgG Fc receptors elicit higher titres of RF when injected in rabbits as compared to group A streptococci without IgG Fc receptors. The streptococcal IgG Fc receptors exhibit a diversity of preferences for subclasses of human IgG, some of them showing allotype preferences. Such allotypes are also recognized by certain RF. IgG RF are able to self-associate thereby forming immune complexes which can activate the complement cascade as well as stimulate release of prostaglandins and (probably) interleukin-1. Since these factors have been assigned an important pathogenic role in rheumatoid arthritis, self-aggregating IgG RF, proposed to be induced by microbial IgG Fc receptors might be an important pathogenic factor in rheumatoid arthritis because rheumatoid arthritis is the only known condition where synthesis of RF takes place in the synovia.

Rheumatoid factor modulation of neutrophil superoxide generation enhancing activity of preformed immune complexes

Heat aggregated human (HAG) IgG pretreated with total rheumatoid factors isolated from the serum of rheumatoid arthritis patients showed decreased superoxide generation enhancing activity as compared with HAG pretreated with buffer alone. Similarly, monoclonal IgM rheumatoid factor isolated from the serum of a patient with macroglobulinemia complicated by rheumatoid arthritis inhibited superoxide generation enhancing activity of HAG. On the other hand, superoxide generation enhancing activity of BSA-antiBSA immune complexes was not affected by preincubation with rheumatoid factors isolated from the sera of either rheumatoid arthritis patients or the macroglobulinemia patient. Rheumatoid factors isolated from rheumatoid arthritis serum were fractionated by high performance liquid chromatography and IgM-class and IgG-class rheumatoid factors were obtained. IgG-class rheumatoid factor significantly enhanced the superoxide generation enhancing activity of HAG, whereas IgM rheumatoid factor inhibited it. Rheumatoid arthritis sera showed significantly higher superoxide generation enhancing activity than normal sera. HAG preincubated with rheumatoid arthritis sera showed significantly lower superoxide generation enhancing activity than HAG preincubated with normal sera. These results suggest that factors inhibiting superoxide generation enhancing activity of HAG are present in rheumatoid arthritis sera, and that the responsible is IgM rheumatoid factor, whereas IgG rheumatoid factor enhances it. The factors that express superoxide generation enhancing activity in rheumatoid arthritis sera are suggested to be intermediate size immune complexes.