Elevated prostaglandin E2 production by monocytes is responsible for the depressed levels of natural killer and lymphokine-activated killer cell function in patients with breast cancer

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Abstract
Background. Human natural killer (NK) cells mediate spontaneous cytotoxicity against tumor cells and represent the main precursors of lymphokine‐activated killer (LAK) cell activity. A comparison of some aspects of NK and LAK cell activity was undertaken in 85 preoperative patients with breast cancer and 75 healthy donors. Methods. NK cell activity (tested in 18‐hour cultures of effector peripheral blood mononuclear cells [PBMC] with K562 or MOLT‐4 tumor target cells) was significantly diminished in these patients as it was the fully mature LAK cell activity (i.e., interleukin‐2 (IL‐2)‐in‐duced cytotoxicity in PBMC) against NK resistant target cells. Using immunoenzymatic methods we showed that the reduced NK cell activity was due to abnormally high levels of prostaglandin E2 (PGE2) produced by monocytes in culture. Results. PGE2 was found to suppress the production of IL‐2 in these cultures. Removal of monocytes from PBMC restored to almost normal levels the deficient NK and LAK cell activity in patients with breast cancer and was also associated with a normalization in the levels of PGE2 and IL‐2. Indomethacin and gamma‐interferon (IFN‐γ) increased the NK and LAK cell activity in these patients up to the levels of healthy donors. When highly purified CD56+ cells (obtained by an immunomagnetic isolation technique) were used as effector cells, no differences in LAK cell activity could be noticed between healthy donors and patients with cancer. FACS and northern blot analyses demonstrated a PGE2‐mediated down‐regulation of IL‐2 receptor (IL‐2R) expression on CD56+ cells that correlated with reduced LAK cell activity. This inhibitory effect of PGE2 was noticeable in long‐term LAK cultures and was abrogated in the presence of IFN‐γ or indomethacin. Conclusion. This study may have important implications in the potentiation of NK and LAK cell activity for immunotherapeutic protocols in patients with breast cancer.