Increased cystatin F levels correlate with decreased cytotoxicity of cytotoxic T cells
Background: Cystatin F is a protein inhibitor of cysteine peptidases that is expressed predominantly in immune cells, localised in the endosomal/lysosomal pathway. In cytotoxic immune cells cystatin F inhibits both the major pro-granzyme convertases, cathepsins C and H, responsible for activation of granzymes, and cathepsin L that is involved in perforin activation. Since perforin/granzyme is one of the main pathways employed for target cell killing by cytotoxic lymphocytes, defects in the activation of either granzymes or perforin can affect their cytotoxic potential.
Methods: A model of reduced T cell cytotoxicity, using TALL-104 cell line treated by ionomycin or by immunosuppressive cytokine transforming growth factor beta was established. Levels of cystatin F were assessed by western blot and interaction of cystatin F with cathepsins C, H and L was analysed. In addition, activities of cathepsins C, H and L and granzyme B in TALL-104 cells were determined.
Results: Reduced cytotoxicity correlated well with increased levels of cystatin F and, consequently, with attenuated specific activities of cathepsins C, H and L and of granzyme B. Co-localisation of cystatin F with cathepsins C, H and L was confirmed, as well as interactions between cystatin F and target cathepsins.
Conclusions: Cystatin F is designated as a possible regulator of T cell cytotoxicity.