MAPKs ERK and p38, but not JNK Phosphorylation, Modulate IL‐6 and TNF‐α Secretion Following OK‐432 In Vitro Stimulation of Purified Human Monocytes

Interaction between the immune system and cancer allows for the use of biological response modifiers, e.g. OK‐432, in cancer therapy. OK‐432, penicillin‐killed Streptococcus pyogenes, is used in treating carcinomas, but also lymphangiomas. We have studied the role of monocytes (MOs) in the immune response to OK‐432 by examining IL‐6 and tumour necrosis factor (TNF)‐α secretion after in vitro MO stimulation with OK‐432, to some extent in comparison with lipoteichoic acid (LTA) and lipopolysaccharide (LPS). LTA stimulation of whole blood gave IL‐6 but not TNF‐α secretion, as previously shown with OK‐432 stimulation, whereas both cytokines were secreted following LPS stimulation. Addition of the MAPK kinase (MAPKK) MEK inhibitor U0126 inhibited IL‐6/TNF‐α secretion in a dose‐dependent manner. Flow cytometry and to some extent Western blot (Wb) analyses showed that MAPK ERK, located downstream of MEK1/2, is predominantly phosphorylated at isolation from peripheral blood. Addition of the p38 MAP kinase inhibitor SB202190 decreased MO IL‐6/TNF‐α production upon OK‐432 stimulation in a dose‐dependent manner. Addition of the MAPK JNK inhibitor SP600125 did not systematically change the MO IL‐6/TNF‐α OK‐432 response. Flow cytometry showed that when stimulating the MOs before isolation from blood, LPS yielded ERK phosphorylation and LPS/LTA p38 phosphorylation, whereas OK‐432 had no effects on phosphorylation levels. In conclusion, we have shown that OK‐432 resembles TLR2 more than TLR4 stimulation of MOs and depends on MAPKK MEK and MAPK p38, but not on JNK phosphorylation. The MEK and p38 MO OK‐432 stimulation dependence is possibly related to the differentiation of cells of the MO lineage.