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Cell-mediated cytotoxicity in perforin-less mice
Abstract:
We have used a perforin-less (PO) mouse to explore alternate CTL-mediated lytic pathways. PO mice are unable to overcome an infection with LCMV in vivo. Nevertheless, splenocytes from infected mice show vigorous, antigen-specific cytotoxicity that requires the presence of the Fas antigen on target cells. The Fas lytic pathway is virtually indistinguishable, in terms of kinetics and magnitude of cytotoxicity, from perforin/granzyme-mediated lysis. It is rapidly induced in CTL upon occupation of the TcR, and requires protein synthesis for full expression. Upon removal of the activating signal, the capacity for fas-mediated lysis rapidly disappears. PO mice infected with LCMV also undergo what appears to be a CD8-mediated immunopathology, and rarely live beyond one month. The precise basis of this pathology is unknown at present. Given the widespread distribution of Fas in mice, particularly on inflamed tissues, the complete failure to clear virus from any tissue or organ is surprising.
Insights
Perforin-less mice demonstrate Fas-mediated cytotoxicity against viral infections, highlighting an alternative pathway for cytotoxic T lymphocytes (CTLs). Despite this, they fail to clear LCMV, suggesting Fas-mediated lysis alone is insufficient for viral clearance.
Area of Science:
- Immunology
- Cellular Biology
- Virology
Background:
- Cytotoxic T lymphocytes (CTLs) are crucial for viral clearance, primarily utilizing the perforin/granzyme pathway.
- Perforin-less (PO) mice provide a model to investigate alternative CTL-mediated lytic mechanisms.
- Lymphocytic choriomeningitis virus (LCMV) infection in PO mice reveals limitations in immune defense.
Purpose of the Study:
- To explore alternative CTL-mediated lytic pathways in the absence of perforin.
- To characterize the role of Fas antigen in CTL cytotoxicity in PO mice during LCMV infection.
- To understand the immunopathology and viral clearance limitations in PO mice.
Main Methods:
- Utilizing perforin-less (PO) mice infected with LCMV.
- Assessing antigen-specific cytotoxicity of splenocytes from infected PO mice.
- Investigating the requirement of Fas antigen and T cell receptor (TcR) signaling for CTL-mediated lysis.
- Monitoring disease progression and survival rates in infected PO mice.
Main Results:
- Splenocytes from infected PO mice exhibit robust, antigen-specific cytotoxicity dependent on Fas.
- Fas-mediated lysis kinetics and magnitude are comparable to perforin/granzyme-mediated lysis.
- Fas-mediated lysis is rapidly induced upon TcR engagement and requires protein synthesis.
- PO mice develop CD8-mediated immunopathology and have a significantly reduced lifespan.
- Despite Fas expression on inflamed tissues, PO mice fail to clear LCMV from any organ.
Conclusions:
- Fas-mediated cytotoxicity represents a significant alternative CTL lytic pathway, compensating for the lack of perforin.
- While Fas-mediated lysis is potent, it is insufficient for complete viral clearance of LCMV.
- The development of immunopathology in PO mice suggests complex immune dysregulation beyond simple lytic pathway deficiency.
- Further research is needed to elucidate the precise mechanisms underlying immunopathology and viral persistence in the absence of perforin.