The regulation of CD95 ligand expression and function in CTL

Area of Science:

• Immunology
• Cellular Biology

Background:

• Previous studies suggested CD95 Ligand (CD95L) expression on cytotoxic T lymphocytes (CTLs) requires new transcription upon target recognition.
• This proposed mechanism aimed to ensure CTL specificity by safeguarding cognate target cell killing.

Purpose of the Study:

• To investigate the regulation of CD95L expression and function in in vivo primed, alloreactive CTLs from perforin-deficient mice.
• To determine if CD95L requires new transcription or can be recruited from preformed stores for CTL-mediated cytotoxicity.

Main Methods:

• Utilized perforin-deficient (P0) mice to isolate alloreactive peritoneal exudate CTLs (PEL).
• Assessed CD95L-mediated cytotoxicity using inhibitors of protein transport (brefeldin A), protein synthesis (emetine), and DNA transcription (actinomycin D).
• Confirmed CD95L mRNA and surface expression via RT-PCR and flow cytometry (Fas-Fc, CD95L Abs).

Main Results:

• CD95L-based cytotoxicity was inhibited by brefeldin A but not by emetine or actinomycin D.
• CD95L mRNA and surface expression were detected in freshly isolated PEL.
• PEL maintained CD95L expression and cytotoxic activity in culture without restimulation.
• PEL exhibited target cell-specific killing, indicating regulation despite functional CD95L.

Conclusions:

• CTLs, specifically PEL, utilize pre-existing CD95L, likely stored in the Golgi or on the cell surface.
• The TCR-triggered recruitment of preformed CD95L, rather than de novo synthesis, controls CD95L-based specific lysis.
• This finding refines the understanding of CTL specificity and cytotoxic mechanisms.