Programmed cell death (apoptosis) can be found in normal thyroid tissue and in various
diseases affecting the thyroid gland. The Fas/Fas ligand (FasL) system is involved
in the induction of apoptosis in human thyrocytes. Cross-linking the Fas receptor
with its own ligand or with an antibody capable of oligomerizing with the receptor
induces programmed cell death. We investigated the role of Fas-induced apoptosis in
primary human thyrocytes in vitro. Cell cultures of normal human thyrocytes were prepared from specimens obtained during
surgery for uninodular goiter. Apoptosis was induced by incubation of the cells with
a monoclonal IgM anti-Fas antibody. The presence of apoptosis was determined by FACS
analysis of FITC-labelled annexin V binding combined with dye exclusion of propidium
iodide. We found a significant rate of Fas-induced apoptosis in normal thyrocytes
after activation with a monoclonal anti-Fas antibody. TSH was able to inhibit Fas-mediated
apoptosis in a dose-dependent manner. This effect was more pronounced when thyrocytes
were incubated in the presence of interferon-γ. Low concentrations of iodine were
able to inhibit apoptosis, while high concentrations of iodine increased the rate
of Fas-induced apoptosis. Our results show that Fas-mediated apoptosis is inducible
in normal human thyrocytes in vitro and is influenced by TSH and iodine. The Fas/FasL system may play an important role
in the regulation of cell number within the thyroid gland, and may be involved in
the processes leading to goiter in iodine deficiency.
Fas - Iodine - Thyrocytes - Apoptosis - TSH
