In vitro and in vivo effects of interferon on the response of human lymphocytes to mitogens.

Previous studies have shown that addition of IFN to the assay in vitro inhibits the proliferative response of lymphocytes to mitogens, whereas long term treatment by IFN in vivo has no major effect on the mitogen responsiveness of tumour patient's lymphocytes. Possible reasons for the discrepancy between the results obtained following treatment by IFN in vitro and in vivo were investigated. It was observed that the proliferative response of tumour patients lymphocytes to various mitogens was not affected to any major extent 24 hr after a single injection of 3 million units of interferon-alpha (IFN-alpha). Lymphocytes from tumour patients and healthy donors were found not to differ in their susceptibility to IFNs' anti-proliferative effect in vitro. Pure IFN-beta, present in the assay throughout the incubation period, inhibited the response of lymphocytes to polyclonal mitogens and PPD showing IFN and not contaminants in the preparations to be responsible for this effect. Although the presence of IFN in the assay throughout the incubation period inhibited the proliferative response of lymphocytes, pre-treatment of these cells with IFN-alpha in vitro was found to have no major effect on their response to mitogens. We conclude that the lack of effect on the proliferative response of lymphocytes following treatment by IFN in vivo, is probably due to the fact that the lymphocytes were only treated with IFN prior to the assay.