Role of bacterial lipopolysaccharide and lymphokine in the regulation of macrophage activation: correlates between secretion of plasminogen activator and tumor lysis.

The effects of bacterial lipopolysaccharide (LPS) and lymphokine (LK) upon the activation of murine C57BL/6 peritoneal macrophages (M phi) were studied. Enhancement of the secretion of plasminogen activator (PA) by lymphokine did not require, nor was significantly boosted by LPS. In contrast, lysis of tumor target cells required LPS in addition to lymphokine confirming prior studies (1-3). Once macrophages were induced to secrete PA, LPS suppressed its release but did not directly interfere with fibrinolysis. These findings are consistent with the concept that induction of PA secretion may represent an earlier step in activation than the acquisition of cytolytic potential (4, 5) and that LPS is important both in the regulation of macrophage proteases and mediation of tumor cell lysis (2, 6).