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

Bacteriological and molecular assessment of staphylococcal enterotoxin e in the blood of patients with rheumatoid arthritis

BACKGROUND

Rheumatoid arthritis (RA) is the most common chronic inflammatory disease of unknown etiology. In this regard, the role of bacterial superantigens (as an effective agent) were considered.

OBJECTIVES

This study aimed to assess staphylococcal enterotoxin E in the blood of patients with rheumatoid arthritis.

PATIENTS AND METHODS

A total of 83 blood samples of patients with RA were studied. All of patient's blood samples have been cultured. Polymerase chain reaction (PCR) and ELISA methods have been used to assess the existence of staphylococcal enterotoxin E (entE). The data were analyzed through descriptive statistics.

RESULTS

During this study and after sequential sub cultures, only 5 bacterial strains were isolated. Based on the results of biochemical tests, just one case was detected as Staphylococcus aureus. The result of molecular diagnosis of enterotoxin E gene was 13.25%. The results of ELISA were 40.96% positive for staphylococcal enterotoxin E.

CONCLUSIONS

In this study, staphylococcal enterotoxin E (superantigen E) was detected in the blood of patients with RA, but its origin is unknown, because no staphylococcus enterotoxin E producer was isolated. This finding could provide a good model for the diagnosis and treatment of RA. However, the results of this study have shown some evidence regarding endogenous origin of involved superantigens in patients with rheumatoid arthritis.

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.

Local production of IgA- and IgM-rheumatoid factors in adult periodontal disease

The enzyme-linked immunospot assay was used to enumerate both the number and the frequency of spontaneous IgG, IgA, and IgM immunoglobulin-secreting cells and IgA- and IgM-rheumatoid factor (RF)-producing cells present in the gingivae and peripheral blood of adult periodontitis patients. Cells from 29 patients were incubated on plates coated with human IgG, Fc, or F(ab')2 fragments and on plates coated with class-specific anti-human antibodies and secreted antibodies were subsequently visualized by means of an immunoenzymatic procedure. The data indicate that (1) IgA-RF- and IgM-RF-secreting cells are frequently present in the gingiva of adult periodontitis patients; (2) production of RF in gingivae of adult periodontitis patients occurs in the absence of demonstrable RF production by simultaneously obtained peripheral blood mononuclear cells, suggesting that local autoimmune reactions may occur in this disease; and (3) lack of correlation between IgA-RF and IgM-RF production in diseased gingiva suggests that the two RF isotypes are regulated independently of each other.

Molecular mimicries between human IgG, IgM rheumatoid factor and streptococcal IgG Fc receptors

A monoclonal IgM rheumatoid factor (RF) from a patient with mixed essential cryoglobulinaemia was found to bind to type M15 group A streptococci with high affinity. The reaction was exerted via the antibody combining sites since it was inhibited by F(ab')2 fragments of anti-idiotypic (Id) antibodies but not by F(ab')2 of anti-IgMFc or normal rabbit IgG. The streptococcal strain also possessed receptors for the Fc part of IgG. IgMRF and IgG attached to different sites on the streptococcal surface, since e.g. anti-Id did not inhibit the IgG Fc-receptor binding. Furthermore, it was found that the interaction between the streptococcal IgG Fc receptor and IgG--like the RF/IgG interaction--took place in the interface between C gamma 2 and C gamma 3 and that histidine 435, tyrosine 436 and/or one both of histidine 433 and 310 were involved.