Inhibitory and stimulatory effects of Pseudomonas aeruginosa pyocyanine on human T and B lymphocytes and human monocytes.

Pyocyanine, a pigment produced by Pseudomonas aeruginosa, has dual dose-dependent stimulatory as well as inhibitory effects on immune responses in vitro as measured by DNA synthesis of human T and B lymphocytes, interleukin-2 (IL-2) production by human T lymphocytes, immunoglobulin production by human B lymphocytes, and monokine production by human monocytes. In general, stimulatory activity was found at low concentrations of pyocyanine, whereas high concentrations of the pigment resulted in an inhibition of responses. At a pyocyanine concentration of 0.1 micrograms/ml or less the proliferation of T and B lymphocytes was enhanced, but at 0.5 micrograms/ml it was suppressed. IL-2 production by T lymphocytes was enhanced at concentrations up to 0.5 micrograms/ml but totally inhibited at 1.0 micrograms/ml. The differentiation of B lymphocytes to become immunoglobulin-producing cells was also enhanced in the presence of low doses of pyocyanine, whereas secretion of immunoglobulin by B lymphocytes was suppressed at all concentrations of pyocyanine. In contrast to the dual effects of pyocyanine on lymphocyte response, lipopolysaccharide-induced IL-1 and tumor necrosis factor release by monocytes was markedly enhanced by low as well as high concentrations of pyocyanine. From these results we conclude that this property of pyocyanine may lead to suppression of specific defense mechanisms and enhance harmful inflammatory reactions of the host during infection with Pseudomonas aeruginosa.