PHAGOCYTIC-ACTIVITY OF FRTL-5 RAT-THYROID FOLLICULAR CELLS AS MEASURED BY INGESTION OF FLUORESCENT LATEX BEADS

A rat thyroid cell line (FRTL-5) was used to study the phagocytic acti vity of thyroid follicular cells using fluorescent latex beads and flo w cytometric analysis. Morphologic studies demonstrated that latex bea ds were engulfed and located within cytoplasmic vacuoles of thyrocytes . Flow cytometric evaluation of cell suspensions revealed high levels of fluorescence in cells engulfing latex beads. Using thyrotropin (TSH ) as a stimulator of thyroid function and human interleukin-1 beta as an inhibitor, protocols were established for measuring the effects of these substances on either basal or TSH-induced phagocytosis. Cells ex posed to latex beads over time in basal (OH) or TSH-containing medium had an increase in time-dependent phagocytic activity which was maxima l after 24 or 8 h, respectively. Treatment of FRTL-5 cells with either a stimulator or an inhibitor revealed maximal change in phagocytic ac tivity after 72 h as measured by the percentage of phagocytic cells as well as the mean fluorescence intensity. Phagocytic activity and iodi de trapping by FRTL-5 cells were qualitatively similar in both sensiti vity and magnitude of change in the assays used in this study. Phagocy tosis of fluorescent latex beads represents a sensitive nonradioactive assay of thyrocyte function whose regulation is similar to iodide tra pping. (C) 1995 Academic Press, Inc.