Acid treatment enhances IL-2 activity of conditioned medium.

Although conditioned medium (CM) from human lymphocytes or mononuclear cells is the most readily available source of interleukin-2 (IL-2) for human T cell culture, its IL-2 activity in our experience is inconsistent. It is likely that this is, at least in part, due to the presence of toxic substances in the CM. Using CM from TPA/SEA induced human mononuclear cells, we have found that acid treatment (pH 2.0, greater than 30 min) significantly improves its ability to promote T cell growth. It is postulated that the selection process which occurs in cultures of mitogen stimulated T cells may result in cells which are sensitive to mitogen-induced lymphotoxins and that these are inactivated by the acid treatment. Since acid treatment did not similarly improve the T cell growth promoting ability of PHA induced, lectin-free commercial IL-2, there must be other differences between it and our CM, which play a role in T cell growth.