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Window of vulnerability of vaccinia virus-infected cells to natural killer (NK) cell-mediated cytolysis correlates
R R Brutkiewicz1, S J Klaus, R M Welsh
1Department of Pathology, University of Massachusetts Medical Center, Worcester 01655.
Abstract:
A time course study was performed in order to determine if vaccinia virus (VV)-infected targets were more susceptible to murine natural killer (NK) cell-mediated lysis during a discrete period of time postinfection. Activated NK cells were used in short-term (e.g. 4 h) assays in order to avoid a further in vitro activation of the NK cells by interferon (IFN) and to test the innate susceptibility of target cells to lysis. The sensitivity of VV-infected L929 cells to lysis by NK cells increased as the infection progressed, reached a peak at approximately 24 h postinfection, and subsequently declined to levels lower than that of uninfected cells. This window of vulnerability was not due to an increase in the number of effector/target cell conjugates, which continually decreased as the VV infection progressed. Triggering of NK cells was measured by the influx of 45Ca2+. Target cells treated with IFN induced less 45Ca2+ uptake, whereas cycloheximide treatment of targets caused a greater influx of 45Ca2+ into the effector cells. When L929 cells were infected with VV for various time intervals and used in the triggering assays, an enhanced triggering of the effectors corresponding to the time of enhanced susceptibility of the target cells to lysis was detected. Quantitative decreases in H-2Kk and Dk class I antigens were observed following VV infection of target cells as measured by FACS analysis using alloantibodies. Qualitative changes in H-2 class I antigens were also observed, as detected by a loss in VV-infected target cell susceptibility to lysis by allospecific cytotoxic T lymphocytes (CTL) at a time when they were highly sensitive to killing by NK cells and VV-specific CTL. These results show that virus-infected targets may become innately more sensitive to lysis by NK cells at discrete time points after infection and that the susceptibility to lysis correlates with enhanced triggering of NK cells and reduced H-2 class I antigen expression.
Insights
Vaccinia virus (VV)-infected cells show increased susceptibility to natural killer (NK) cell lysis during a specific 24-hour window post-infection. This enhanced killing correlates with NK cell triggering and reduced MHC class I expression on infected targets.
Area of Science:
- Immunology
- Virology
- Cell Biology
Background:
- Natural killer (NK) cells are crucial for innate immunity against viral infections.
- Viral infections can modulate host cell susceptibility to immune responses.
- Understanding the dynamics of NK cell-mediated lysis of virus-infected cells is vital for immune evasion strategies.
Purpose of the Study:
- To determine the temporal susceptibility of vaccinia virus (VV)-infected cells to murine NK cell-mediated lysis.
- To investigate the mechanisms underlying this susceptibility, including effector-target cell conjugation and NK cell triggering.
- To analyze changes in host cell surface antigen expression post-VV infection.
Main Methods:
- Time-course study of VV-infected L929 cells incubated with activated NK cells in short-term 45Ca2+ influx assays.
- Measurement of effector/target cell conjugate formation.
- Flow cytometry (FACS) analysis of H-2Kk and Dk class I antigen expression.
- Assessment of susceptibility to lysis by allospecific cytotoxic T lymphocytes (CTL).
Main Results:
- VV-infected cells exhibited increased sensitivity to NK cell lysis, peaking around 24 hours post-infection.
- This heightened susceptibility was associated with enhanced NK cell triggering (45Ca2+ influx), not increased conjugate formation.
- VV infection led to quantitative and qualitative down-regulation of H-2 class I antigens, affecting CTL recognition but not NK cell sensitivity.
- Infected cells showed reduced susceptibility to CTLs while becoming more sensitive to NK cell-mediated killing.
Conclusions:
- Virus-infected target cells can exhibit innate susceptibility to NK cell lysis at specific time points post-infection.
- This transient vulnerability is linked to enhanced NK cell triggering and a decrease in MHC class I expression.
- NK cells play a critical role in controlling viral infections by targeting infected cells during specific windows of susceptibility.