Determination of IgG subclasses and avidity of antithyroid peroxidase antibodies in patients with subclinical hypothyroidism - a comparison with patients with overt hypothyroidism.
OBJECTIVE
To evaluate the immunoglobulin G subclasses of anti-TPO and antibody avidity in patients with subclinical hypothyroidism (sH), overt hypothyroidism (H) and a control group (C).


METHODS
According to the TSH, fT4 and anti-TPO antibody levels, appraised by immunometric assays, 95 female patients were divided into three groups (sH, H and C). IgG subclass levels and avidity were measured by a homemade ELISA. Results were analyzed by nonparametric tests and Spearman's rank correlation.


RESULTS
The predominant IgG subclasses detected in both case groups were IgG1 and IgG4 with a significantly higher level of IgG4 in the sH group. Consequently, the IgG1/IgG4 ratio was significantly lower in sH patients.


CONCLUSIONS
The higher levels of IgG4 anti-TPO reduced significantly the IgG1/IgG4 ratio in sH patients. These results permit to envisage that increasing this ratio could be useful as a positive predictive factor for the development of overt disease in such patients.
Silva
L M
LM
Department of Internal Medicine - Endocrinology, Vale do Itajaí University, Itajaí Brazil. lireda@melim.com.br
Chavez
J
J
Canalli
M H B
MH
Zanetti
C R
CR
D000328:Adult; D000368:Aged; D019138:Antibodies, Blocking / Q000276:immunology*; D000915:Antibody Affinity / Q000502:physiology*; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D006801:Humans; D007037:Hypothyroidism / Q000276:immunology*; D007074:Immunoglobulin G / Q000032:analysis / Q000145:classification / Q000276:immunology*; D007453:Iodide Peroxidase / Q000276:immunology*; D008875:Middle Aged; D011237:Predictive Value of Tests; D013960:Thyroid Function Tests; D013967:Thyroiditis, Autoimmune / Q000276:immunology*; D013972:Thyrotropin / Q000097:blood; D013974:Thyroxine / Q000097:blood
D019138:Antibodies, Blocking; D007074:Immunoglobulin G; D013972:Thyrotropin; D007453:Iodide Peroxidase; D013974:Thyroxine