Expression of rheumatoid factor idiotypes 17.109, 6B6.6 and 4C9 in the sera of Pima Indians

Hypothesis: the humoral immune response to oral bacteria provides a stimulus for the development of rheumatoid arthritis

Rheumatoid arthritis (RA) and adult periodontitis share common pathogenetic mechanisms and immunologic and pathological findings. One oral pathogen strongly implicated in the pathogenesis of periodontal disease, Porphyromonas gingivalis, possesses a unique microbial enzyme, peptidylarginine deiminase (PAD), the human equivalent of which has been identified as a susceptibility factor for RA. We suggest that individuals predisposed to periodontal infection are exposed to antigens generated by PAD, with de-iminated fibrin as a likely candidate, which become systemic immunogens and lead to intraarticular inflammation. PAD engendered antigens lead to production of rheumatoid factor-containing immune complexes and provoke local inflammation, both in gingiva and synovium via Fc and C5a receptors.

Inter-relationships between rheumatoid arthritis and periodontal disease. A review

This review considers the considerable similarities between periodontal disease and rheumatoid arthritis (RA). While the etiology of these two diseases may differ, the underlying pathogenic mechanisms are remarkably similar and it is possible that individuals manifesting both periodontitis and RA may suffer from a unifying underlying systemic dysregulation of the inflammatory response. In light of these findings, the implications for the use of disease-modifying medications in the management of these two chronic inflammatory conditions is apparent. Further longitudinal studies and medication-based intervention studies are required to determine just how closely these two conditions are allied.

A rheumatoid factor specific mimotope identified by a peptide display library

We screened a 10 amino acid peptide display library in filamentous phage with B'20, a monoclonal high affinity IgM rheumatoid factor (RF) expressing the VkIIIa-dependent 4C9 idiotype. Using direct and indirect selection techniques, 12 B'20 reactive peptides were identified, 9 of which belonged to one of two motifs. Binding of B'20 to phage-bearing peptides was inhibited by both IgG and 4C9 antiidiotype. Synthetic peptides corresponding to the two motifs inhibited the Fc binding of a low avidity IgA B'20 construct. Purified IgM from 6/8 RF-positive RA patients and 8/11 monoclonal RFs with VkIII-encoded light chains bound to the phage, whereas none of the four monoclonal RFs with VkI or VkII encoded light chains bound. Phage binding appeared to be RF specific. Three 4C9 positive/RF negative cell lines from RA patients did not bind to phage nor did three B'20 mutants that had lost RF specificity, whereas two mutants that retained RF specificity also retained phage binding. We propose that there is a common epitope(s) recognized by VkIII encoded RFs that is mimicked by the structure of these peptides. Such mimotopes might be exploited to design novel agents that interfere with autoantibody binding.

Rheumatoid factor from periodontitis patients cross-reacts with epitopes on oral bacteria

OBJECTIVES

The objective of this study was to determine the antigenic specificity of rheumatoid factor (RF) that had previously been reported in the serum of patients with periodontitis.

DESIGN

IgM-RF was isolated from the serum of five RF-seropositive rheumatoid arthritis patients and 14 RF-seropositive periodontitis and examined for specificity to human IgG and selected oral bacteria.

METHODS

IgM-RF was prepared by affinity chromatography on human IgG columns. Human IgG antibody to Capnocytophaga gingivalis, Fusobacterium nucleatum, and Actinobacillus actinomycetemcomitans was isolated by binding and elution of antibody from the bacteria, followed by purification using a rabbit anti-IgG affinity column.

MAIN OUTCOME MEASURE

Binding of the isolated IgM-RF was determined using an enzyme-linked immunosorbent assay (ELISA). The antigens used for detection of binding included isolated human IgG, human IgG antibody bound to the bacteria, and the bacteria alone. Inhibition of the IgM-RF binding with IgG or Fc gamma was used to assess the specificity of the reactivity with IgG and/or the bacteria.

RESULTS

The results showed that the IgM-RF reacted with polyclonal human IgG nonspecifically bound to microtiter plates. The reactivity of the IgM-RF was increased when incubated with IgG that bound as antibody to C. gingivalis, F. nucleatum or A. actinomycetemcomitans. However, the IgM-RF did not bind with increased intensity to the specific IgG antibody preparations or to IgG preparations lacking antibody to these micro-organisms. Additionally, the IgM-RF preparations bound to surface components of both C. gingivalis and F. nucleatum. Blocking studies showed that Fc gamma but not IgG inhibited IgM-RF binding to both micro-organisms.

CONCLUSIONS

These findings indicate that the RF detected in the serum of some periodontitis patients may be elicited by certain micro-organisms in the subgingival plaque. Furthermore, C. gingivalis and F. nucleatum appear to express surface antigen epitopes that are antigenically related to determinants on IgG can induce cross-reactive IgM-RF.

Molecular characterization of monoclonal IgM derived from human B cell lines expressing the 4C9 rheumatoid factor associated idiotype

Ten human monoclonal B cell lines that express the RF associated Id 4C9 were analyzed using an immunogenetic approach. Five of eight tested lines were also strongly positive for the 6B6.6 Id. We found that all the 4C9/6B6.6 positive lines expressed VkIIIa light chain genes. In contrast, 4C9 reactivity was also found on a cell line expressing a VkIIIb light chain gene and on a line expressing a V light chain gene. The two anti-Ids recognized a linear light chain determinant on Humkv328 encoded light chains but also a conformational determinant on Vg encoded light chains that appeared to be dependent on the presence of a heavy chain. Idiotypic reactivity occurred on both RF positive and RF negative antibodies. Within this idiotypic system, the basis for idiotypic reactivity and RF reactivity is complex, subject to both heavy and light chain gene usage and sensitive to small numbers of somatic mutations.