The decreased growth rate of obese strain chicken thyroid cells provides in vitro evidence for a primary target organ abnormality in chickens susceptible to autoimmune thyroiditis.

The obese (OS) strain of chickens develops severe autoimmune thyroiditis, whereas its progenitor, the Cornell (CS) strain, rarely does. To detect possible developmental abnormalities in the OS thyroid, CS and OS embryonic thyroid epithelia were cultured in vitro and compared in several assays for growth and DNA metabolism. It was found that OS thyroid cells incorporated less tritiated thymidine, reached lower saturation densities, and possessed a significantly longer doubling time (26.1 hr) than CS cells (17.6 hr). The decreased growth rate of OS thyroid cells correlated with their inability to condition their own media. These abnormalities in the embryonic development of OS thyroid cells were discussed in the context of factors predisposing to autoimmune thyroiditis.