Journal of Virology, February 2001, p. 1124-1131, Vol. 75, No. 3
0022-538X/01/$04.00+0 DOI: 10.1128/JVI.75.3.1124-1131.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Department of Virology1 and Department of Neuroscience,2 Lerner Research Institute, The Cleveland Clinic Foundation, Cleveland, Ohio 44195
Received 1 June 2000/Accepted 2 November 2000
Human parainfluenza virus type 3 (HPIV3) is one of the major causes
of bronchiolitis, pneumonia, and croup in newborns and infants.
Cellular immunity involving major histocompatibility complex (MHC)
class I and class II molecules plays an important role in controlling
virus infection. Several viruses have been shown to down-regulate gamma
interferon (IFN-
)-mediated MHC class II expression. In this
communication, we show that HPIV3 strongly inhibits the IFN-
-induced
MHC class II expression in HT1080 human fibrosarcoma cells. The culture
supernatant of HPIV3-infected cells also inhibited IFN-
-induced MHC
class II expression, a phenomenon that was found to be due, in large
part, to alpha/beta interferon (IFN-
/
). Expression of MHC class I
and intercellular adhesion molecule 1 occurred efficiently in cells
simultaneously infected with HPIV3 and treated with IFN-
, indicating
that the inhibitory effect of HPIV3 was specific to MHC class II. STAT1 activation was not affected by HPIV3 at early postinfection times but
was partially inhibited at later times. These data suggested that the
potent inhibition of MHC class II expression was, in major part, due to
a defect downstream of STAT1 activation in the IFN-
-induced MHC
class II expression pathway. Class II transactivator (CIITA) is the
unique mediator of IFN-
-induced transcription from the MHC class II
promoter. By RNase protection analysis, CIITA expression was found to
be strongly inhibited in HPIV3-infected cells. The culture supernatant
containing IFN-
/
, on the other hand, inhibited MHC class II
expression without affecting STAT1 and CIITA expression. These data
indicate that HPIV3 inhibits IFN-
-induced MHC class II expression
primarily by the viral gene products targeting CIITA and additionally
by inducing IFN-
/
to target one or more steps further downstream.
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