The effect of phorbol myristate acetate on human lymphocytes: An ultrastructural study

Phorbol myristate acetate (PMA), a tumour promoter, acts as an agglutinin and as a stimulator of human lymphocytes. Agglutination begins within 1 hr and is macroscopically evident within 24 hr. The ultrastructural findings in lymphocytes stimulated with PMA after 48 and 72 hr show blast transformation of the nucleus, increase in cytoplasm and in ribosomes, and occasional “annulate lamellae.” Apart from the finding of “annulate lamellae” the changes are generally similar to those found in PHA stimulated lymphocytes. The function and significance of the “annulate lamellae” are not known but as they have been most often seen in malignant and embryonal cells they may be representative of a more fundamental dedifferentiation of the cells with PMA as opposed to PHA.