Relationship Between Thyroid Autoantibody Spectrotype and IgG Subclass

Abstract

The relationship between spectrotype and IgG subclass of autoantibodies to thyroglobulin (Tg) and thyroid peroxidase (TPO) has been investigated using sera from Hashimoto and Graves' patients. Isoelectric focussing (IEF) was carried out in gels over the range pI 3.5–9.5 followed by transblotting to nitrocellulose and probing the filters using ¹²⁵I-labelled TPO and Tg. As has been shown previously for Tg antibodies, TPO antibody focussed over different pl values in different patients but the spectrotypes for individuals were constant over 2–5 years. Further, the pI values for TPO and Tg autoantibodies appeared to be related to IgG subclass, for example IgGl Tg antibodies tended to focus nearer the cathode (PI 8.0–9.5) than IgG4 antibodies (PI 6.5–8.5) while antibodies of subclasses IgGl +2 + 4 produced spectrotypes covering a broad pI range (5.7–9.5). Consequently, it seems likely that the characteristic spectrotypes described by others for Tg autoantibodies. and those we now report for TPO antibodies, reflect the IgG subclass “fingerprints” which we suggest may be a measure of the ability of an individual to respond to different epitopes on these two thyroid antigens.

Key Words:

• Autoimmune thyroid disease
• IgG subclasses
• isoelectric focussing (IEF)
• spectrotype
• thyroglobulin autoantibody
• thyroid peroxidase autoantibody