Evidence for multiple lytic pathways used by cytotoxic T lymphocytes

Area of Science:

• Immunology
• Cellular Biology

Background:

• Previous research questioned the role of degranulation in cytotoxic T-lymphocyte (CTL) mediated cytotoxicity.
• This study provides a deeper investigation into CTL lysis mechanisms.

Purpose of the Study:

• To elucidate the distinct pathways utilized by CTLs for target cell lysis.
• To investigate the role of degranulation, calcium (Ca2+), and protein kinase C (PKC) activity in CTL-mediated cytotoxicity.

Main Methods:

• CTL-mediated lysis was analyzed using three inhibitors: 4,4'-diisothiocyano-2,2'-disulfonic acid stilbene, EGTA (to chelate Ca2+), and prolonged PMA exposure to exhaust PKC.
• The dependence of lysis pathways on Ca2+, PMA sensitivity, degranulation, and protein synthesis was assessed.

Main Results:

• Three distinct CTL lysis pathways were identified: Pathway I (Ca2+-dependent, PMA-sensitive, degranulation-independent), Pathway II (Ca2+-independent, PMA-insensitive, degranulation-independent), and a third pathway involving degranulation observed in some CTL clones.
• Pathway I is the primary mechanism for most target cells, while Pathway II is induced by specific target cells, leading to the apparent shutdown of Pathway I.
• Pathway II does not require protein synthesis and results in target cell DNA solubilization.

Conclusions:

• CTLs employ multiple, distinct pathways for target cell lysis, with degranulation not being a universal requirement.
• The induction of a Ca2+-independent lysis pathway (Pathway II) highlights the adaptability of CTLs in targeting specific cells.
• A subset of CTLs utilizes a degranulation-dependent pathway, potentially influenced by interleukin-2 (IL-2) levels.