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Reactivity of agalactosyl IgG with rheumatoid factor
Yuji Imafuku1, Hiroshi Yoshida, Yuji Yamada
1Department of Clinical Laboratory Medicine, Fukushima Medical University, 1-Hikarigaoka, 960-1247, Fukushima, Japan. yuji@fmu.ac.jp
Background:
The difference in the reactivity of rheumatoid factor (RF) with agalactosyl IgG and galactosyl or intact IgG is controversial.
Methods:
ELISAs for IgM-RF, using agalactosyl IgG and galactosyl IgG as a coated antigen, were developed. The sera of patients with RA, systemic lupus erythematosus (SLE), chronic liver diseases (CLD) and healthy subjects were measured for IgM-RF. An absorption test was performed using these IgGs with or without heat-pretreatment to determine any differences in the antigenicity between agalactosyl IgG and intact IgG.
Results:
IgM-RF titers were higher against agalactosyl IgG than those against both heated-intact and intact IgG in three of nine RA patients' sera. Three other serum samples showed similar titers against all three forms of IgG and the remaining three serum samples showed varied results. IgM-RF titers were higher in sera of RA patients than those of SLE, CLD and healthy subjects. Absorptions of RA sera showed that RF was completely absorbed by 5x of absorptions with agalactosyl IgG as well as intact IgG.
Conclusions:
The reactivity of IgM-RF is higher with agalactosyl IgG than with heated-intact or intact IgG. The antigenic epitopes of agalactosyl and intact IgG were shown to be closely similar by the absorption test.