Linoleic Acid Inhibition of Naturally Occurring Lymphocytotoxicity to Breast Cancer-Derived Cells Measured by a Chromium-51 Release Assay2

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Abstract
Long-chain unsaturated free fatty acids have been shown to inhibit the immune responses of lymphocytes in vivo and in transformation and macrophage inhibition factor assays in vitro. The purpose of this study was to test the effect of linoleic acid on naturally occurring lymphocytotoxicity in a 51Cr release microcytotoxicity assay with the use of a human breast carcinoma cell line (AlAb) as source of the target cells. In the presence of increasing concentrations of linoleic acid, a linear decrease in lymphocytotoxicity was observed with complete inhibition at concentrations of 0.05–0.07 mg/ml. Concentrations of linoleic acid greater than 0.07 mg/ml resulted in nonspecific toxicity to target cells but not to lymphocytes as determined by trypan blue exclusion tests. When lymphocytes were pretreated with linoleic acid, washed, and then tested for cytotoxicity in the absence of linoleic acid, suppression of lymphocytotoxicity was still demonstrated. When leukocytes were depleted of macrophages, cytotoxicity in the absence of linoleic acid was enhanced 50–100%; complete inhibition of cytotoxicity was still observed at 0.05 mg linoleic acid/ml. When B- and T-cell populations were separated, each population showed typical decreases in lymphocytotoxicity in the presence of linoleic acid; however, the B-cell fraction (containing “null” cells) was two to three times more efficient at cell killing than was the T-cell fraction.

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