Effect of Pokeweed Mitogen (pwm) on Lymphocyte Lysosomes

Resting blood lymphocytes in vitro undergo transformation into large, blastlike, dividing cells following incubation with phytohemagglutinin (PHA), a plant lectin from Phaseolus vulgaris (1). Farnes et al. (2) found another phytomitogen in saline extracts of the plant Phytolacca americana (pokeweed). Although both PHA and the pokeweed mitogen (PWM) induce nonspecific transformation of lymphocytes which differs markedly from specific transformation by antigens (3), the chemical composition and the biological effects of these agents are by no means entirely identical. PWM has been shown to possess a molecular weight much lower than that of PHA (4, 10), and to induce in vitro the formation not only of blasts like PHA-induced ones but also of a unique intermediate-sized cell type with cytoarchitectural features of plasmablasts (5). In previous studies (6, 7), we have demonstrated the presence in human peripheral blood lymphocytes of acid hydrolase-rich granules which display many of the biochemical and structural characteristics of lysosomes in other tissues. Between 30 and 120 min after addition of PHA to intact, purified lymphocytes, redistribution of acid hydrolases (beta-glucuronidase, acid phosphatase) from a 20,000 g X 20 min granular fraction into the corresponding supernatant was observed. These changes were associated with increased fragility of hydrolase-rich granules derived from PHA-stimulated lymphocytes upon subsequent incubation with membrane-disruptive agents in vitro. For these, and other reasons, it was suggested that redistribution of acid hydrolases may play a role in remodeling processes of lymphocytes stimulated by PHA (6, 7). As a necessary test of this hypothesis, we have, therefore, determined whether pokeweed mitogen could also produce changes in enzyme distribution among subcellular fractions of human lymphocytes. MATERIALS AND METHODS