Further studies on ring shaped nucleoli and micronucleoli of human peripheral lymphocytes

Peripheral human lymphocytes were studied in short term tissue cultures to provide more information on the relationship between ring shaped nucleoli and micronucleoli in these cells. The cultivation of peripheral lymphocytes with actinomycin D produced a transformation of ring shaped nucleoli to micronucleoli. Therefore, nucleolar types and particularly micronucleoli cannot indicate the lymphocytic origin. THe horse-shoe like nucleoli or beaded ring shaped nucleoli possibly represent intermediate nucleolar stages between ring shaped nucleoli and micronucleoli. Ring shaped nucleoli apparently reflect low nucleolar RNA synthesis and micronucleoli a complete inhibition of this process.