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Published on: January 2, 2013
Functional defects of NK cells treated with chloroquine mimic the lytic defects observed in perforin-deficient mice
M Austin Taylor1, M Bennett, V Kumar
1Graduate Program in Immunology, Department of Pathology, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA. austin01@utsw.swmed.edu
Abstract:
NK cells are the primary effectors mediating acute rejection of incompatible bone marrow cell grafts. To reduce rejection, we evaluated the ability of chloroquine (CHQ) to prevent perforin-dependent NK cell activity. Perforin is a key cytotoxic component released from the lytic granules of activated NK cells. Generation of functional perforin requires an acidic protease activity that occurs in the secretory, lytic lysosomes. Our hypothesis was that CHQ, a lysosomotropic reagent, would raise the pH of the acidic compartment in which perforin is processed and thereby block perforin maturation and cytotoxicity. We have measured NK cytotoxicity in vivo by clearance of YAC-1 tumor cells from the lungs and by rejection of incompatible bone marrow transplants and in vitro by cytolysis of YAC-1 and Jurkat cells. The engraftment of bone marrow cells was monitored by recolonization of the spleen with hemopoietic cells from transplants of MHC class I-deficient bone marrow cells into lethally irradiated recipient mice. Transplant rejection was compared in two inbred strains of mice: 129, which apparently use perforin-dependent cytotoxicity, and C57BL/6, in which rejection can be perforin-independent. CHQ treatment reduced NK cell activity in 129 mice in which perforin is important for mediating rejection. CHQ affected the fraction of NK cell cytolysis that was Fas independent. In addition, we found that CHQ prevents perforin processing by LAK cells in vitro. These data indicate that CHQ may impair rejection of incompatible bone marrow transplants and other functions mediated by NK and cytotoxic T cells.
Insights
Chloroquine (CHQ) can reduce NK cell activity by preventing perforin maturation, a key molecule in transplant rejection. This study shows CHQ may help prevent bone marrow transplant rejection and other immune responses.
Area of Science:
- Immunology
- Cell Biology
- Pharmacology
Background:
- Natural Killer (NK) cells are crucial in acute rejection of incompatible bone marrow transplants.
- Perforin is a key cytotoxic protein released by NK cells, essential for graft rejection.
- Perforin maturation relies on acidic conditions within secretory lysosomes.
Purpose of the Study:
- To investigate if chloroquine (CHQ) can inhibit perforin-dependent NK cell activity and reduce transplant rejection.
- To determine if CHQ, as a lysosomotropic reagent, interferes with perforin processing by altering lysosomal pH.
Main Methods:
- NK cell cytotoxicity was assessed in vivo (tumor cell clearance, bone marrow transplant rejection) and in vitro (cell lysis assays).
- Bone marrow engraftment was monitored in mice following transplantation of MHC class I-deficient cells.
- Transplant rejection was compared between mouse strains with perforin-dependent (129) and perforin-independent (C57BL/6) NK cell activity.
Main Results:
- CHQ treatment significantly reduced NK cell activity in 129 mice, where perforin-dependent cytotoxicity is critical for rejection.
- CHQ impacted the Fas-independent component of NK cell-mediated cytolysis.
- In vitro experiments demonstrated that CHQ inhibits perforin processing by lymphokine-activated killer (LAK) cells.
Conclusions:
- Chloroquine impairs perforin maturation and NK cell cytotoxicity, potentially by increasing lysosomal pH.
- CHQ shows promise in reducing the rejection of incompatible bone marrow transplants.
- The findings suggest CHQ could be a therapeutic agent to modulate NK and cytotoxic T cell functions.
