PSEUDOMONAS-AERUGINOSA EXOENZYME-S INDUCES PROLIFERATION OF HUMAN T-LYMPHOCYTES

Pseudomonas aeruginosa is a gram-negative bacterium that is responsibl e for devastating acute and chronic infections, which include bronchie ctasis in cystic fibrosis, nosocomial pneumonia, and infection of burn wounds. Previous studies have demonstrated that these patients have i mpaired host responses, including cell-mediated immune responses, whic h are important in anti-Pseudomonas host defense. The P. aeruginosa ex oproduct, exoenzyme S, has a number of characteristics which suggest t hat it might be important in cell-mediated immunity. To determine whet her exoenzyme S activates lymphocytes to proliferate, peripheral blood mononuclear cells (PBMC) from normal volunteers were stimulated with purified exoenzyme S, and the lymphocyte response was assessed by meas uring [H-3]thymidine uptake and by counting the number of cells after various times in culture. Ninety-five percent of healthy adult donors had a lymphocyte response to exoenzyme S, The optimal lymphocyte respo nse occurred on day 7, with 4 x 10(5) PBMC per microtiter well when ce lls were stimulated with 10 mu g exoenzyme S per mi, [H-3]thymidine up take correlated with an increase in the number of mononuclear cells, i ndicating that proliferation occurred, In unseparated PBMC, T cells, a nd to a lesser extent B cells, proliferated. Purified T cells prolifer ated, while purified B cells proliferated only after the addition of i rradiated T cells. Thus, T lymphocytes are necessary and sufficient fo r the proliferative response to exoenzyme S, We speculate that exoenzy me S from P. aeruginosa is important in T-lymphocyte-mediated host def ense to P. aeruginosa, In strategies to enhance impaired cell-mediated immunity, exoenzyme S should be considered as a potential stimulant.