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Journal of Virology, February 2000, p. 1985-1993, Vol. 74, No. 4
Institute for Virology and Immunobiology,
University of Würzburg, D-97078
Würzburg,1 and Institute for
Virology, University of Marburg, D-35011
Marburg,2 Germany
Received 16 August 1999/Accepted 22 November 1999
Immunosuppression induced by measles virus (MV) is associated with
unresponsiveness of peripheral blood lymphocytes (PBL) to mitogenic
stimulation ex vivo and in vitro. In mixed lymphocyte cultures and in
an experimental animal model, the expression of the MV glycoproteins on
the surface of UV-inactivated MV particles, MV-infected cells, or cells
transfected to coexpress the MV fusion (F) and the hemagglutinin (H)
proteins was found to be necessary and sufficient for this phenomenon.
We now show that MV fusion-inhibitory peptides do not interfere with
the induction of immunosuppression in vitro, indicating that MV
F-H-mediated fusion is essentially not involved in this process.
Proteolytic cleavage of MV F0 protein by cellular
proteases, such as furin, into the F1-F2
subunits is, however, an absolute requirement, since (i) the inhibitory activity of MV-infected BJAB cells was significantly impaired in the
presence of a furin-inhibitory peptide and (ii) cells expressing or
viruses containing uncleaved F0 proteins revealed a
strongly reduced inhibitory activity which was improved following
trypsin treatment. The low inhibitory activity of effector structures containing mainly F0 proteins was not due to an impaired
F0-H interaction, since both surface expression and
cocapping efficiencies were similar to those found with the authentic
MV F and H proteins. These results indicate that the fusogenic activity
of the MV F-H complexes can be uncoupled from their immunosuppressive
activity and that the immunosuppressive domains of these proteins are
exposed only after proteolytic activation of the MV F0 protein.
0022-538X/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Proteolytic Cleavage of the Fusion Protein but Not
Membrane Fusion Is Required for Measles Virus-Induced Immunosuppression
In Vitro
*
Corresponding author. Mailing address: Institute for
Virology of the University of Würzburg, Versbacher Str. 7, D-97078 Würzburg, Germany. Phone: 49-931-201-3895. Fax:
49-931-201-3934. E-mail: s-s-s{at}vim.uni-wuerzburg.de.
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