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Infect Immun, April 1998, p. 1299-1308, Vol. 66, No. 4
0019-9567/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Glycosphingolipids as Novel Targets for T-Cell
Suppression by the B Subunit of Recombinant Heat-Labile
Enterotoxin
Robert L.
Truitt,1,2,3,*
Carrie
Hanke,1
Jay
Radke,2
Reinhold
Mueller,1,2 and
Joseph T.
Barbieri2,3
Department of
Pediatrics,1
Department of
Microbiology,2 and
Cancer
Center,3 Medical College of Wisconsin,
Milwaukee, Wisconsin
Received 20 October 1997/Returned for modification 11 December
1997/Accepted 8 January 1998
Heat-labile enterotoxin subunit B (LTB) is a noncatalytic protein
derived from Escherichia coli that binds to ganglioside GM1, a glycosphingolipid on the surface of mammalian cells.
In this study, the effects of recombinant LTB (rLTB) on murine
lymphocytes were examined in vitro. T and B cells readily bound
fluorescein isothiocyanate-labeled rLTB. CD8+ T
cells bound twice as much as CD4+ T cells and B cells.
Exposure of T-cell subsets and B cells to rLTB abrogated
mitogen-driven proliferation. CD8+ T cells were more
susceptible to rLTB than either CD4+ T cells or B
cells. There were differences in the sensitivity of lymphocytes from
various strains of mice to rLTB. This was attributed to qualitative and
quantitative differences in the CD4+ T cells. rLTB
induced apoptosis in both T-cell subsets, but the level was
significantly higher in CD8+ T cells. Apoptosis peaked
at around 8 h after exposure to rLTB and incubation at
37°C. Binding to ganglioside GM1 was essential for
suppression, since rLTB/G33D, a mutant which does not bind GM1, failed to inhibit proliferation or induce
apoptosis. Naive T cells, which were acutely sensitive to rLTB,
became more resistant after activation. Conversely,
activated T cells regained their sensitivity to rLTB when they reverted
back to a resting state. A 1-h pulse with rLTB was sufficient to
inhibit T-cell proliferation and cytotoxic-T-lymphocyte generation in
primary mixed lymphocyte reaction cultures. CD8+ T cells
were preferentially depleted in these cultures. rLTB also induced
functional modifications in T cells as indicated by inhibition of
gamma interferon secretion after polyclonal activation. Thus,
rLTB may have immunomodulatory properties independent of its ability to
induce apoptosis.
*
Corresponding author. Mailing address: Department of
Pediatrics, Medical College of Wisconsin, 8701 Watertown Plank Rd.,
Milwaukee, WI 53226. Phone: (414) 456-4163. Fax: (414) 456-6543. E-mail: rtruitt{at}mcw.edu.
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