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Spontaneous Cytotoxicity (SCMC) of Normal Human Lymphocytes against a Human Melanoma Cell Line: A Phenomenon Due to a Lymphotoxin-Like Mediator¹

From the Department für Klinische Immunologie und Transfusionsmedizin der Medizinischen Hochschule, D-3000 Hannover, West-Germany and Kinderklinik der Universität München, D-8000 München 2 Lindwurmstrasse 4, West-Germany

Abstract

Spontaneous cell-mediated cytotoxicity (SCMC) of normal human lymphocytes against various allogenic tumor cell lines has recently been identified as a non-T lymphocyte function. In this study evidence is presented that SCMC against a human melanoma cell line (IGR3) involves a nonspecific lymphotoxin-like mediator(s) (LT), which is rapidly produced by lymphocytes that are retained on IgG-anti-IgG columns. LT was shown to inhibit in 48-hr cultures the DNA synthesis of growing IGR3 and HeLa cell monolayers. Furthermore, in short term ⁵¹Cr-release assays using IGR3 target cells, LT increased strongly the SCMC of normal allogeneic lymphocytes, although it exhibited little cytotoxicity by itself in this assay. LT was detectable in cell-free supernatants harvested after 6 hr from co-cultures of IGR3 melanoma cells and normal effector lymphocytes, but not in supernatants from melanoma cells alone or lymphocytes alone. Lymphocyte preparations that had been passed through IgG-anti-IgG columns had lost the capacity to generate LT and were poor effectors in SCMC. However, in the presence of LT, a small proportion of null cells, which pass through IgG-anti-IgG columns, was capable of inducing strong SCMC. Absorption of the supernatants, containing LT activity, with an insolubilized rabbit-anti-human IgG antiserum did not remove the mediator, suggesting that it is not an immunoglobulin.

Footnotes

¹ This work was supported by the Deutsche Forschungsgemeinschaft, personal grants Pe 151/3, Ei 106/3 and Ka 325/4.