Late-phase expression of a murine cytomegalovirus immediate-early antigen recognized by cytolytic T lymphocytes

The cloned murine cytolytic T-lymphocyte line IE1-IL and several
sublines detect a murine cytomegalovirus immediate-early (IE)
membrane determinant in conjunction with Ld class I major
histocompatibility glycoprotein. The lines retained cytolytic
activity, strict antigen specificity, and self-restriction even
when adapted to long-term, antigen-independent growth in the
presence of interleukin-2 only (M. J. Reddehase, H.-J. Bühring, and
U. H. Koszinowski, J. Virol. 57:408-412). These attributes allowed
us to use IE1-IL as a stable, monospecific probe for tracing the
expression of the IE membrane antigen throughout the viral
replication cycle. Presentation of the antigen at the cell membrane
proved to be most effective when expression of IE genes in infected
mouse embryo fibroblasts was selectively enhanced by consecutive
cycloheximide-actinomycin D treatment, whereas without enhancement
high numbers of IE1-IL cytolytic T lymphocytes were required to
demonstrate the antigen in the IE phase. In the early phase of
infection when IE genes were no longer transcribed, cytolysis was
not observed, although IE proteins were detectable in the nuclei of
the infected cells. Without application of inhibitors IE membrane
antigen expression was most prominent during the late phase of
infection. Reinitiation of transcription from the genomic region
encoding the major IE protein (pp89) and de novo synthesis of pp89
correlated with this reexpression of the IE membrane antigen.