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Prostaglandin E₂ Suppresses NK Activity In Vivo and Promotes Postoperative Tumor Metastasis in Rats

From the Neuroimmunology Research Unit (IY, RM, GS, KS, ER, NA, SB-E), Department of Psychology, Tel Aviv University, Tel Aviv, Israel; and School of Nursing (GGP), Johns Hopkins University, Baltimore, Maryland.

Correspondence: Address correspondence and reprint requests to: Shamgar Ben-Eliyahu, PhD, Department of Psychology, Tel Aviv University, Tel Aviv 69978, Israel; Fax: 972-3-640-9547; E-mail: shamgar{at}post.tau.ac.il

Background: Prostaglandins (PGs) were shown in vitro to suppress several functions of cellular immunity. It is unclear, however, whether physiological levels of PGs can suppress cellular immunity in vivo and whether such suppression would compromise postoperative host resistance to metastasis.

Methods: Fischer 344 rats were administered PGE₂ in doses (18 to 300 µg/kg subcutaneously) that increased the serum levels approximately 2- to 4-fold. We then assessed the number and activity of circulating natural killer (NK) cells, as well as rats’ resistance to experimental metastasis of a syngeneic NK-sensitive tumor (MADB106). To study whether endogenously released PGs after surgery compromise these indices, we tested whether laparotomy adversely affects them and whether a cyclooxygenase-synthesis inhibitor, indomethacin (4 mg/kg), attenuates these effects.

Results: PGE₂ dose-dependently suppressed NK activity per NK cell and dose-dependently increased 4- and 24-hour MADB106 lung tumor retention (LTR); 240 µg/kg of PGE₂ quadrupled the number of lung metastases counted 3 weeks later. Selective depletion of NK cells abrogated the promotion of LTR by PGE₂. Surgery significantly suppressed NK activity and increased MADB106 LTR, and indomethacin halved these effects without affecting nonoperated rats.

Conclusions: PGE₂ is a potent in vivo suppressor of NK activity, and its postoperative release may promote tumor recurrence.

Key Words: Animals • NK cells • Cytotoxicity • Tumor immunology

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