Influence of interleukin 6 on the function of secondary cultures of human thyrocytes

Interleukin 6 has been suggested as second mediator of the effects of interleukin 1 in some cell systems. Interleukin 1 has previously been shown to inhibit the function of human thyrocytes in secondary cultures. We have therefore studied the influence of interleukin 6 (10(-1)-5.10(7) U/l) on the function of thyroid cells. Recombinant interleukin 6 slightly inhibited the production of cAMP, but failed to influence the production of thyroglobulin or the DNA content. Endotoxins (lipopolysaccharides from Salmonella abortus equi or Yersinia enterocolitica) had only a slightly inhibitory effect on thyroid cell functions, and the effect of interleukin 6 could not by itself be explained by endotoxin contamination. The effect of interleukin 6 did not mimic effects on thyroid cells afforded by recombinant interleukin 1 alpha and 1 beta. Furthermore, antibodies to interleukin 6 were not able to inhibit the interleukin 1 beta-induced inhibition of thyroid cell functions. In conclusion, it is unlikely that interleukin 6 by itself mediates the biological effects of interleukin 1 on human thyroid cells.