Inhibitory effects of mitogens on adenoidal lymphocytes in vitro

Cultures of human adenoidal lymphocytes exposed briefly to either phytohemagglutinin (PHA), Staphylococcus filtrate (Staph-F), concanavalin-A (Con-A), or pokeweed mitogen (PWM) incorporate increased amounts of thymidine earlier than replicate cultures exposed continuously to the mitogens. These effects can begin in the first 24 hr of culture and are seen maximally between 36 and 72 hr. Once a blastogenic response is established, PHA or PWM can diminish that response. Inhibition with PWM requires that the initial stimulation was with this mitogen, while PHA can inhibit blastogenesis to both PHA and PWM-stimulated cells. Because these mitogens can have a paradoxical effect on adenoidal lymphocytes, being capable of both initiating and inhibiting DNA synthesis, this phenomena should be kept in mind when such systems are utilized for the evaluation of antigens and drug effects.