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Infect. Immun., May 1995, 1800-1805, Vol 63, No. 5
CH Mody, DE Buser, RM Syme and DE Woods
Pseudomonas aeruginosa is a gram-negative bacterium that is responsible for
devastating acute and chronic infections, which include bronchiectasis in
cystic fibrosis, nosocomial pneumonia, and infection of burn wounds.
Previous studies have demonstrated that these patients have impaired host
responses, including cell-mediated immune responses, which are important in
anti-Pseudomonas host defense. The P. aeruginosa exoproduct, exoenzyme S,
has a number of characteristics which suggest that it might be important in
cell-mediated immunity. To determine whether 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 measuring [3H]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 response occurred on day 7, with 4 x 10(5) PBMC per
microtiter well when cells were stimulated with 10 micrograms exoenzyme S
per ml. [3H]thymidine uptake correlated with an increase in the number of
mononuclear cells, indicating that proliferation occurred. In unseparated
PBMC, T cells, and to a lesser extent B cells, proliferated. Purified T
cells proliferated, while purified B cells proliferated only after the
addition of irradiated T cells. Thus, T lymphocytes are necessary and
sufficient for the proliferative response to exoenzyme S. We speculate that
exoenzyme S from P. aeruginosa is important in T-lymphocyte-mediated host
defense to P. aeruginosa. In strategies to enhance impaired cell-mediated
immunity, exoenzyme S should be considered as a potential stimulant.
Copyright © 1995, American Society for Microbiology
Pseudomonas aeruginosa exoenzyme S induces proliferation of human T lymphocytes
Department of Internal Medicine, University of Calgary, Alberta, Canada.
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