Affinity Purification of IgG Subclasses and the Distribution of Thyroid Auto‐Antibody Reactivity in Hashimoto's Thyroiditis

Abstract

To delineate accurately the IgG subclass distribution of thyroid auto-antibodies, sera from nine patients with Hashimoto's thyroiditis were fractionated into IgG subclasses by complete depletion of the other IgG subclasses on affinity columns. All IgG subclass fractions contained thyroglobulin and microsomal (or thyroid peroxidase) antibody activity, although when compared to the total serum concentrations of IgG subclasses, IgG4 antibodies were overrepresented. However, in contrast to recent studies, this particular subclass never predominated--IgG4 antibody levels being exceeded by those of the IgG1 and IgG2 subclasses; it seems likely that these differences relate to varying sensitivity for different subclasses in previously used assay methods. This pattern of subclass activity differed from that of tetanus toxoid antibodies, which were found in six subjects. There was no light chain restriction within any subclass, showing that the overproduction of IgG4 thyroid antibodies is not of monoclonal origin. The functional affinity of subclasses for both thyroid antigens varied between patients, but IgG2 subclass fractions showed the highest functional affinity in the majority of samples. We also found that IgG2 subclass thyroid antibodies were ineffective in eliciting antibody-dependent cell-mediated cytotoxicity, as distinct from the other three subclasses. Our results show that thyroid antibodies are less restricted in their IgG subclass distribution and patients are less heterogeneous than previously described. Moreover, IgG2 thyroid antibodies are quantitatively important and differ in relative functional affinity and effector function from IgG1 and IgG4 thyroid antibodies.

Comparison of the IgG Subclass Distribution of Anti-thyroid Peroxidase Antibodies in Healthy Subjects with That in Patients with Chronic Thyrolditis.

“…Dilutions of the monoclonal antibodies to the IgG subclasses were as follows: HP6001 (anti-IgGI) 1/2,000; HP6008 (anti-IgG2) 1/2,000; CG-01 (anti-IgG3) 1/3,000; DG-01 (anti-IgG4) 1/4,000. The results are expressed in a similar manner to those reported by Weetman et al [7] as follows: the absorbances given by all four IgG subclass-specific monoclonals are summed and the individual absorbances are expressed as a percentage of this total. Determinations of all four subclasses were done simultaneously and the percentage distribution of antibody activity within each subclass was calculated when the total of the absorbances for all four subclasses was higher than 1.0.…”

“…On the one hand, Kotani et al [1 2] reported that anti-TPO antibodies consisted mainly of the IgGI subclass, followed by the IgG2 subclass, although TPO is the major antigen in microsomes. A recent report by Weetman et al [7] showed that antibodies to Tg and Mc were less restricted in their IgG subclass distribution than previously described. Our data concerning the distribution of the IgG subclasses of anti-TPO antibodies in patients with chronic thyroiditis closely resemble those of anti-Mc antibodies reported by Parkes et al [10] or Jansson et al [ 11 ].…”

Recognition by recombinant autoimmune thyroid disease-derived Fab fragments of a dominant conformational epitope on human thyroid peroxidase.

“…Sera from individual patients contain different proportions of TPO antibodies of subclasses IgG1 and IgG4 and, in some patients, IgG2 (32,38 9 sera analyzed are shown (Fig. 6).…”

“…Thus, in some patients the SP epitope is predominantly IgGl, in others IgG4, and in a few IgG2. IgG3 TPO autoantibodies are only rarely present (32,38). There is no information on the IgG subclass distribution or light chain type of autoantibodies against the linear epitopes described above.…”

The presence of thyroid peroxidase antibody of IgG2 subclass is a risk factor for thyroid dysfunction in chronic hepatitis C patients

“…Our previous study on 168 newly diagnosed Hashimoto's thyroiditis patients demonstrated that the prevalence of TPOAb IgG2 subclass was significantly higher in hypothyroidism (51.5%) and subclinical hypothyroidism (33.3%) than in euthyroidism (11.9%) (39). Weetman et al (40) IgG2 had the highest relative functional affinity and differed in effector function from IgG1 and IgG4 thyroid antibodies. IgG2 expression is induced by IFN-gamma (IFN-g) (41).…”