TNF-alpha is secreted by monocytes in transit to become macrophages, but not by peripheral blood monocytes, following OK-432 (lyophilized S. pyogenes) stimulation.

OK-432, penicillin-killed Streptococcus pyogenes, is used in treating lymphangiomas and carcinomas. We have studied proinflammatory interleukin (IL) secretion following OK-432 stimulation of total blood, peripheral blood mononuclear cell (PBMC) and purified monocytes in vitro. OK-432 stimulation of purified monocytes gave IL-1beta, IL-1RA, IL-6, IL-12p40 and tumour necrosis factor (TNF)-alpha response. OK-432 stimulation of cells within blood did, however, not yield TNF-alpha secretion. When PBMC or monocytes were cultured in low-attachment wells a decreased IL secretion was observed compared to adherent cells. Inhibition of Syk kinase with piceatannol, only at high, non-specific doses, but not PI3 kinase inhibition with LY294002 or Wortmannin, decreased monocyte IL response to OK-432. This shows that beta(1-3)-integrin receptor function is not necessary for monocyte OK-432-stimulated TNF-alpha secretion. Direct blockage of the beta(2)-integrin (CD18) receptor by anti-CD18 antibody was also unable to prevent the stimulating effects of OK-432 in human monocytes. On the other hand, Syk phosphorylation is elevated upon adherence of monocytes and this is further increased by OK-432 stimulation, as shown by Western blot. The Fc-receptor was also ruled out as a main receptor of the OK-432 monocyte response. In conclusion, TNF-alpha secretion is only found in monocytes removed from blood. This TNF-alpha secretion is not mediated through the beta(1-3)-integrin receptors. OK-432 may act as a target-seeking substance whereby only monocytes adhered, e.g. to a tumour cell, become cytotoxic in part explaining why OK-432 is well suited as a cancer treatment drug.