Incidence of anti-mouse IgG in normal subjects and patients with autoimmune thyroid disease.

Serum antibodies to mouse IgG occasionally interfere with two-site immunometric assays in which mouse monoclonal antibodies are used. We examined the titers of antibodies to mouse IgG in serum samples from normal subjects and patients with autoimmune thyroid disease (AITD) using an enzyme-linked immunosorbent assay. Anti-mouse IgG antibodies were positive in 7/119 patients with Graves' disease (5.9%) and 3/60 patients with Hashimoto's thyroiditis (5.0%). One of the 15 patients with a thyroid neoplasm (6.7%) also had antibodies to mouse IgG, as did 5/60 healthy subjects (8.3%). These antibodies were either of the IgG or IgM class. There was no significant difference in the incidence of positive anti-mouse IgG antibody between normal subjects and patients with AITD. It is important to note this high incidence of antibodies to mouse IgG due to the potential of interference with immunometric assays employing mouse monoclonal antibodies.