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.
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.
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.
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.
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.
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.