Dextran sulfate acts as an endothelial cell protectant and inhibits human complement and natural killer cell-mediated cytotoxicity against porcine cells.
BACKGROUND
The innate immune system, including complement and natural killer (NK) cells, plays a critical role in activation and damage of endothelial cells (ECs) during xenograft rejection. The semisynthetic proteoglycan analog dextran sulfate (DXS, molecular weight 5,000) is known to inhibit the complement and coagulation cascades. We hypothesized that DXS may act as an "EC-protectant" preventing complement and NK lysis by functionally replacing heparan sulfate proteoglycans that are shed from the EC surface on activation of the endothelium.


METHODS
Binding of DXS to ECs, deposition of human complement, cytotoxicity, and heparan sulfate expression after exposure to normal human serum were analyzed by flow cytometry. The efficacy of DXS to protect ECs from xenogeneic NK cell-mediated cytotoxicity was tested in standard 51Cr-release assays.


RESULTS
DXS dose-dependently inhibited all three pathways of complement activation. Binding of DXS to porcine cells increased on treatment with human serum or heparinase I and correlated positively with the inhibition of human complement deposition. This cytoprotective effect of DXS was still present when the challenge with normal human serum was performed up to 48 hr after DXS treatment of the cells. DXS incubation of porcine ECs with and without prior tumor necrosis factor-alpha stimulation reduced xenogeneic cytotoxicity mediated by human NK cells by 47.3% and 25.3%, respectively.


CONCLUSIONS
DXS binds to porcine cells and protects them from complement- and NK cell-mediated injury in vitro. It might therefore be used as a novel therapeutic strategy to prevent xenograft rejection and has potential for clinical application as an "EC protectant."
D000818:Animals; D000925:Anticoagulants / Q000378:metabolism / Q000494:pharmacology*; D001011:Aorta / Q000166:cytology; D001798:Blood Proteins / Q000494:pharmacology; D002478:Cells, Cultured; D003167:Complement Activation / Q000187:drug effects; D003169:Complement Inactivator Proteins / Q000494:pharmacology*; D016264:Dextran Sulfate / Q000378:metabolism / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004730:Endothelium, Vascular / Q000166:cytology / Q000187:drug effects* / Q000276:immunology; D006084:Graft Rejection / Q000188:drug therapy / Q000276:immunology; D019763:Heparin Lyase / Q000494:pharmacology; D006801:Humans; D066298:In Vitro Techniques; D007694:Killer Cells, Natural / Q000187:drug effects* / Q000276:immunology; D013552:Swine; D014183:Transplantation, Heterologous / Q000276:immunology
D000925:Anticoagulants; D001798:Blood Proteins; D003169:Complement Inactivator Proteins; D016264:Dextran Sulfate; D019763:Heparin Lyase