Circular dichroism of immune complexes with rheumatoid factor activity

Area of Science:

• Immunology
• Structural Biology
• Biochemistry

Background:

• Rheumatoid factor (RF) activity is associated with certain immunoglobulin G (IgG) complexes.
• The structural integrity of IgG in these complexes has not been fully elucidated.
• Circular dichroism (CD) spectroscopy is a sensitive method for assessing protein secondary and tertiary structures.

Purpose of the Study:

• To compare the circular dichroism (CD) spectra of IgG complexes with RF activity and monomeric IgG without RF activity.
• To investigate the structural characteristics of immunoglobulins isolated from RF-active IgG complexes.
• To determine if unique structural features exist in RF-associated IgG.

Main Methods:

• Isolation of IgG complexes with RF activity and monomeric IgG from the same individual's serum.
• Circular dichroism (CD) spectroscopy was employed to analyze IgG structure in the near and far ultraviolet regions.
• Specific antiserum was used to isolate immunoglobulins with unique determinants from RF-active IgG complexes.

Main Results:

• IgG complexes with RF activity exhibited significantly deviant CD spectra in the near UV region compared to monomeric IgG.
• Deviant CD spectra were observed both before and after dissociation of the RF-active IgG complexes.
• Immunoglobulins isolated using specific antiserum showed distinct CD spectra in the far UV region, differing from both normal IgG and other RF-active IgG.

Conclusions:

• The structure of IgG in RF-active complexes is significantly different from that of normal IgG.
• Unique structural conformations are present in specific immunoglobulins associated with RF activity.
• These findings confirm structural alterations in IgG involved in RF activity and highlight distinct structural subsets within RF-associated immunoglobulins.