Abstract
Phenazine pigments secreted by P.aeruginosa inhibit lymphocyte blastogenic responses. We studied the mechanism of inhibition of two model compound, PYO and OHP on the T-cell cycle. Peripheral blood mononuclear cells (PBMC) were stimulated with the mitogen, Concanavalin A (Con A) or with the following steps of T-cell activation were studied: 1. Increase in cytosolic-free Ca2+ using Quin-2 fluorescence. 2. Production of Interleukin 2 (IL-2) using the CTLL-20 cell line. 3. Expression of IL-2 receptors (IL-2R) using monoclonal antibodies and flow cytometry. 4). Uptake of 3H-Thymidine (3HTdR). Results with Con A activated PBMC are shown in the table.Lower concentrations of PYO and OHP inhibited Con A-induced 3H TdR uptake synergistically. In ionomycin-activated blastogenesis, 3H TdR uptake was strongly inhibited by PYO (94%), but only to a minor degree by OHP (30%). Therefore, PYO and OHP inhibit T-cell activation at different steps of the signal transduction pathway. OHP blocks the increase in cytosolic Ca2+ and PYO acts at a later step not by-passed by ionomycin. Locally secreted phenazine pigments, even in small amount, may act synergistically to inhibit cellular immune responses necessary to eradicate chronic infections with P.aeruginosa.
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