Granzyme A-deficient mice retain potent cell-mediated cytotoxicity

Area of Science:

• Immunology
• Cellular Biology
• Molecular Biology

Background:

• Granzyme A, a serine proteinase in cytotoxic T lymphocytes and natural killer cells, was thought to be crucial for target cell DNA fragmentation.
• Its precise biological role in cell-mediated cytotoxicity remained to be fully elucidated.

Purpose of the Study:

• To investigate the in vivo biological function of Granzyme A.
• To determine if Granzyme A is essential for cell-mediated cytotoxicity.

Main Methods:

• Generation of Granzyme A-deficient mouse models using homologous recombination.
• Confirmation of Granzyme A absence via Western blot, enzyme assays, and RT-PCR.
• Assessment of cytotoxic T cell and natural killer cell functions in vitro and ex vivo.
• Evaluation of Granzyme A-deficient mice in viral (LCMV) and bacterial (Listeria) infection models, and in syngeneic tumor eradication.

Main Results:

• Granzyme A-deficient mice were generated and confirmed to lack Granzyme A expression in activated T cells.
• Deletion of Granzyme A did not affect the expression of other granule components (granzymes B-G, perforin).
• Granzyme A-deficient mice displayed normal hematopoietic development and health.
• Cytotoxic T cells and natural killer cells from deficient mice showed comparable membrane disruption, apoptosis, and DNA fragmentation capabilities.
• Granzyme A-deficient mice effectively cleared viral and bacterial infections and eradicated tumors similarly to wild-type mice.

Conclusions:

• Granzyme A is not essential for the primary mechanisms of cell-mediated cytotoxicity, including target cell apoptosis and DNA fragmentation.
• The study challenges the long-held assumption of Granzyme A's critical role in immune surveillance and effector functions.
• Granzyme A-deficient mice serve as a valuable model for further dissecting the nuances of immune cell-mediated killing.