Cathepsin-B-dependent apoptosis triggered by antithymocyte globulins: a novel mechanism of T-cell depletion.
Antithymocyte globulins (ATGs), the immunoglobulin G (IgG) fraction of sera from rabbits or horses immunized with human thymocytes or T-cell lines, are used in conditioning regimens for bone marrow transplantation, in the treatment of acute graft-versus-host disease, in the prevention or treatment of acute rejection in organ transplantation, and in severe bone marrow aplasia. In nonhuman primates, ATGs induce rapid, dose-dependent, T-cell depletion in peripheral lymphoid tissues, where apoptotic cells can be demonstrated in T-cell zones. We show here that increasing ATG concentrations in vitro resulted in reduced lymphocyte proliferative responses, associated with a rapid increase in the percentage of apoptotic cells. Apoptosis did not require prior exposure to interleukin-2, nor did it result in CD178/CD95 or tumor necrosis factor/tumor necrosis factor receptor (TNF/TNF-R) interactions; it was therefore clearly different from activation-induced cell death. Cytochrome c release, caspase-9, and caspase-3 activation were not implicated, excluding a direct involvement of the intrinsic mitochondrial pathway. The cysteine protease inhibitor E64d and cathepsin-B-specific inhibitors conferred significant protection, whereas apoptosis was associated with the release of active cathepsin B into the cytosol. These data demonstrate a role for cathepsin B in T-cell apoptosis induced by ATGs at concentrations achieved during clinical use.
Michallet
Marie-Cécile
MC
Laboratoire d'Immunopharmacologie, Institut National de la Santé et de la Recherche Médicale U503 and U404, Centre d'Etudes et de Recherche en Virologie et Immunologie, Lyon, France.
Saltel
Frederic
F
Preville
Xavier
X
Flacher
Monique
M
Revillard
Jean-Pierre
JP
Genestier
Laurent
L
D000961:Antilymphocyte Serum / Q000008:administration & dosage / Q000494:pharmacology*; D017209:Apoptosis; D020169:Caspases; D002401:Cathepsin B / Q000378:metabolism / Q000502:physiology*; D045304:Cytochromes c; D003600:Cytosol; D004305:Dose-Response Relationship, Drug; D006801:Humans; D008213:Lymphocyte Activation / Q000187:drug effects; D008212:Lymphocyte Depletion / Q000379:methods*; D008247:Lysosomes; D013601:T-Lymphocytes / Q000166:cytology
D000961:Antilymphocyte Serum; D045304:Cytochromes c; D020169:Caspases; D002401:Cathepsin B