Control of human thyroid autoantibody production in SCID mice

In order to determine the phenotype of the cells required for thyroid autoantibody production, peripheral blood mononuclear cells (PBMC) from patients with autoimmune thyroid disease (AITD) were transferred to severe combined immunodeficient (SCID) mice. The production of human IgG, thyroglobulin (Tg) antibody and thyroid peroxidase (TPO) antibody in the SCID recipients was monitored for up to 4 months. PBMC from 10 of 13 AITD patients produced substantial IgG (> or = 100 micrograms/ml) and detectable Tg and TPO antibodies in recipient mice. PBMC pretreated to deplete or enrich T cells produced low or undetectable thyroid-specific antibody in SCID mice. Depletion of CD4+ T cells resulted in much lower or undetectable IgG, Tg and TPO antibodies compared with levels seen in recipients of control PBMC. By contrast, depletion of CD8+ T cells from the PBMC had no overall effect on autoantibody production, although with PBMC from some patients CD8+ depletion possibly enhanced both IgG and autoantibody production. In eight of 10 experiments, autoantibody levels reached maximal titres before total IgG levels peaked. It is considered that thyroid autoantibodies are produced from memory B cells activated in SCID mice and that this activation is T cell- and CD4+ T cell-dependent.