Effect of Pseudomonas aeruginosa exotoxin a on PHA-induced lymphocyte proliferation.

P. aeruginosa Exotoxin A induced a dose dependent suppression of PHA-stimulated human lymphocyte proliferation. The suppressor effect was not reversed by interleukin 2 (IL-2) added to the culture medium. Expression of IL-2 receptors (IL-2R) on PHA-blasts a well as their ability for IL-2 binding were decreased by Exotoxin A. Kinetic studies of IL-2 production showed that IL-2 activity was still present in cultures of lymphocytes activated for 72 hours with PHA and Exotoxin A. In contrast, supernatants of lymphocyte cultures activated with PHA and Exotoxin A for 18 hours had low activity of IL-2. Hence, Exotoxin A probably could decrease the utilization of IL-2 due to either inhibition of IL-2R expression or suppression of their ability for IL-2 binding.