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Infect. Immun., Jun 1996, 1937-1943, Vol 64, No. 6
A Darji, A Beschin, M Sileghem, H Heremans, L Brys and P De Baetselier
Experimental infections of mice with the African trypanosome Trypanosoma
brucei lead to a profound state of T-cell unresponsiveness in the lymph
node cell (LNC) compartment. This suppression is mediated by
macrophage-like cells which inhibit interleukin 2 (IL-2) secretion and
down-regulate IL-2 receptor expression (M. Sileghem, A. Darji, R. Hamers,
M. Van de Winkel, and P. De Baetselier, Eur. J. Immunol. 19:829- 835,
1989). Similar suppressive cells can be generated in vitro by pulsing
2C11-12 macrophage hybridoma cells with opsonized T. brucei parasites
(2C11-12P cells). Cocultures of 2C11-12P cells and LNCs secrete higher
levels of gamma interferon (IFN-gamma), and the hyperproduction of
IFN-gamma was found to be confined to CD8+ lymphoid cells. Elimination of
CD8+ cells from cocultures of 2C11-12P cells and LNCs restores the T-cell
proliferative response. Furthermore, addition of neutralizing
anti-IFN-gamma antibodies to the cocultures reduces the level of
suppression and concomitantly restores the level of IL-2 receptor
expression. Hence, IFN-gamma plays a cardinal role in this in vitro model
for T. brucei-elicited immunosuppression. Cocultures of LNCs and 2C11-12P
cells in a two-chamber culture system further demonstrated that cell-cell
contact is required for hyperproduction of IFN-gamma and, moreover, that
IFN-gamma cooperates with a 2C11-12P- derived diffusible factor to exert
its suppressive activity. Finally, tumor necrosis factor alpha (TNF-alpha
produced by 2C11-12P cells was found to be implicated in the
hyperproduction of IFN-gamma, since addition of neutralizing anti-TNF-alpha
antibodies to cocultures reduced the level of suppression and concomitantly
abrogated the hyperproduction of IFN-gamma. Collectively, our findings
indicate that T. brucei-elicited suppressive 2C11-12 macrophage cells
differentially influence T-cell subpopulations: (i) CD8+ cells are signaled
via cell- cell contact to produce IFN-gamma, and TNF-alpha is implicated in
this process, and (ii) locally produced IFN-gamma and macrophage-released
factors act in concert to inhibit CD4+ and CD8+ T-cell proliferative
responses.
Copyright © 1996, American Society for Microbiology
In vitro simulation of immunosuppression caused by Trypanosoma brucei: active involvement of gamma interferon and tumor necrosis factor in the pathway of suppression
Unit of Cellular Immunology, Flemish Interuniversity Institute of Biotechnology, University of Brussels (V.U.B.), Sint Genesius Rode, Belgium.
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