Functional channel formation associated with cytotoxic T-cell granules

Area of Science:

• Immunology
• Cell Biology
• Biophysics

Background:

• Cytotoxic T-lymphocytes (CTLs) are crucial for adaptive immunity.
• CTLs induce target cell death through granule exocytosis.
• The precise mechanism of CTL-mediated cytolysis remains under investigation.

Purpose of the Study:

• To investigate the functional and structural properties of cytotoxic T-lymphocyte granules.
• To determine if these granules form ion channels and their characteristics.
• To explore the role of these channels in T-cell mediated cytotoxicity.

Main Methods:

• Subcellular fractionation using Percoll gradients to enrich lymphocyte granules.
• Assays for hemolytic activity and membrane depolarization.
• Planar bilayer electrophysiology to characterize ion channel formation.
• Transmission electron microscopy for ultrastructural analysis of granule proteins.

Main Results:

• Granule-enriched fractions exhibited potent hemolytic activity in the presence of calcium (Ca2+).
• Isolated granules induced rapid, Ca2+-dependent membrane depolarization in J774 macrophage-like cells.
• Granules formed large-conductance (1-6 nS) Ca2+-dependent ion channels in planar bilayers.
• These channels were poorly selective, permeable to monovalent and divalent ions, and resistant to potential-induced closing.
• Ultrastructural analysis revealed ring-like structures in granule proteins incubated with Ca2+.

Conclusions:

• Cytotoxic T-lymphocyte granules can form functional, Ca2+-dependent ion channels.
• These channels exhibit properties consistent with a role in the cytolytic process.
• The formation of these channels and associated structures may be a key mechanism in CTL-induced cell death.