Modulation of natural and interleukin-2-induced tumour-cytolytic activities by the members of a protein family related to beta-thromboglobulin.

A preparation of three C-terminal fragments of the platelet protein beta-thromboglobulin was previously described to have immunomodulatory properties on phagocytic cells. One of the components is obviously identical to the recently described neutrophil-activating peptide 2 (NAP-2). In further investigations on this protein preparation (called factor C) we are able to show an additional influence on the tumour-cytolytic activities of mononuclear cells. Total neutralization of the factor C effect, by treating a factor C preparation with specific monoclonal antibody C24 prior to application in cell culture, proved that the effect is really restricted to factor C proteins. If factor C is given in combination with natural interleukin-2 (IL-2) a dose-dependent suppression of IL-2-mediated natural killer lymphokine-activated killer activity can be measured, which is first detectable 72 h after addition of factor C. Suppression does not occur if the both factors are added within a time interval of more than 12 h. Depletion of monocytes from mononuclear cells has no effect on factor-C-mediated cytotoxicity, demonstrating that factor C acts directly on lymphoid cells.