A study of the kinetics of RNA and DNA synthesis in PWM-stimulated lymphocytes revealed that RNA synthesis preceded the onset of DNA synthesis by approximately 24 hr and that DNA synthesis and transformation was maximal between 66 to 78 hr. Histochemical and radioautographic studies on PWM stimulated cultures indicated that at 72 hr 50 to 60% of the cell population had been transformed by PWM, and that a distinct cell type bearing cytologic resemblance to the early plasma cell had emerged. The RNA sedimentation profile for newly synthesized RNA in PWM-stimulated cells showed that a large peak of 45 to 50 S material was formed after 24 and 40 hr. PWM thus produces a distinctive transformation of human peripheral blood lymphocytes.

Plant lectins with blood group specificity for mammalian red cells were first described more than 50 years ago (1). As part of this body of knowledge it is of special interest that in 1908 Landsteiner and Raubitschek (2) demonstrated the presence of a panhemagglutinin in saline extracts of the red kidney bean, Phaseolus vulgaris. In succeeding decades an increasing number of plant lectins were identified. However, it was only in 1960 that the lectin from Phaseolus vulgaris, phytohemagglutinin (PHA) was recognized as being distinctive by virtue of its possessing the additional properties of leukagglutination (3, 4) and mitogenic activities for human peripheral blood lymphocytes (5-10). For a time it appeared that among an extensive spectrum of plant lectins PHA might be unique in this regard. However, Fames et al. (11) have recently reported that extracts of Phytolacca americana, pokeweed (PWM), although apparently lacking hemagglutinafing and leukagglutinating activity induced transformation of human lymphocytes in vitro. In this laboratory, further studies of the properties of the pokeweed extracts disclosed that this material did in fact possess hemagglutinating and leukagglutinating activities; moreover, it was ascertained that the properties of pokeweed differed from PHA in a number of important respects.In this report we will present data on the biological and chemical properties of the pokeweed mitogen and in the subsequent papers, consider the unique cytologic, biochemical, and fine structural features of the PWM-transformed cells (12, 13).

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