Fourier-transform infrared spectroscopy of human IgG Fc fragments, which are a promising drug for the treatment of autoimmune diseases.

IgG Fc fragments that expose regulatory rheumatoid factor epitopes (regRF epitopes) have emerged as a promising immunosuppressive drug. Immunization of rats with such Fc fragments reduced symptoms of experimental autoimmune diseases. The immunosuppressive effect of Fc fragments is based on stimulating the production of regRF, which kills activated CD4 T lymphocytes. The formation of regRF epitopes on Fc fragments was previously shown to be associated with a reduction in disulfide bonds in the fragments' hinge region. However, the structure of Fc fragments that bear regRF epitopes remained largely unclear. Infrared spectra were compared for lyophilized Fc fragments displaying regRF epitopes and Fc fragments without such epitopes. FTIR spectroscopy found no differences in the amide I, amide II, and amide III bands, indicating that there are no distinctive features in the secondary structure of Fc fragments bearing regRF epitopes. The distinctive feature of Fc fragments bearing regRF epitopes, irrespective of whether the free SH groups in the hinge were preserved or lost after lyophilization, is the presence of a band or a fine structure in the region containing the bending vibrations of the SH groups. Furthermore, the Fc fragments with regRF epitopes differ from those without in that they have a band in the absorption region of aromatic amino acid rings. Taken together, these facts suggest that the appearance of regRF epitopes results from changes in the tertiary structure of the hinge and the domains that occur when the hinge is reduced, and they also indicate that these conformational changes are resistant to subsequent changes in the state of cysteine residues in the hinge. Bands in the regions of aromatic amino acids and the bending vibrations of SH groups are markers of the presence of regRF epitopes on IgG Fc fragments. FTIR spectroscopy can be used to detect these epitopes.

Regulatory and other rheumatoid factors in rheumatoid arthritis patients with active disease or in remission.

BACKGROUND: Previously, we identified a regulatory rheumatoid factor (regRF), the production of which provides rats with resistance to collagen-induced arthritis (CIA). Immunization with conformers of IgG Fc fragments carrying epitopes specific to regRF reduces symptoms of CIA. The aim of this study was to determine whether there is a link between regRF levels and rheumatoid arthritis (RA) activity in humans in order to assess the potential of regRF as a therapeutic biotarget in RA. The variability of rheumatoid factor (RF) specificities present in the blood of RA patients was also studied. METHODS: The regRF were studied in RA patients with active disease and in remission. Variability in the specificities of RF associated with RA was studied by concurrent inhibition of RF latex fixation by variants of modified IgG. RESULTS: Patients in remission had regRF levels higher than in healthy subjects. The regRF in remission was characterized by tight binding to its antigen, as in healthy subjects. The regRF levels in patients with active RA varied dramatically, and regRF binding to its antigen was weak. The exacerbation of Still's disease coincided with low regRF levels and affinity, while an improvement in patient condition was associated with an increase in regRF levels and affinity. The RF specific to RA, which was detected by the RF latex-fixation method, was a nonhomogeneous population of antibodies that included RF to lyophilized IgG, to IgG immobilized on polystyrene, and to rabbit IgG. CONCLUSION: Stimulating regRF production might enable improved RA therapy.

Suppression of experimental autoimmune encephalomyelitis by IgG Fc fragments bearing regRF epitopes.

Previously we identified a rheumatoid factor, the production of which provides rats with resistance to experimental autoimmune diseases. It has been named regulatory rheumatoid factor (regRF). Immunization with conformers of IgG Fc fragments carrying epitopes specific to regRF reduces rat collagen-induced arthritis. The aim of this study was to determine whether IgG Fc fragments bearing regRF epitopes suppress experimental autoimmune encephalomyelitis, and to evaluate the potential of a strategy of stimulating production of regRF to treat multiple sclerosis. Two days after myelin basic protein injection, rats were immunized with Fc fragments exhibiting regRF epitopes, as well as with Fc fragments without those epitopes. The effect of Fc immunization on clinical signs of EAE and immunological parameters was evaluated. Stimulation of regRF production by IgG Fc fragments bearing regRF epitopes diminished EAE symptoms in rats, while immunization with Fc fragments without those epitopes worsened EAE. The improvement of EAE symptoms in rats treated with Fc fragments bearing regRF epitopes was associated with regRF production and with the relatively low number of blood CD4 T lymphocytes during disease development. In experiments involving immunizing intact rats and lymph node mononuclear cell cultures, Fc fragments bearing regRF epitopes decreased the CD4 T lymphocyte population indirectly, via regRF production. RegRF is a promising biotarget in MS, and Fc fragments bearing regRF epitopes are a potential therapeutic agent for MS.