Suppressive effect of CTB glycoprotein (75 kDa) on IL-4 expression in primary-cultured lymphocytes treated with di(2-ethylhexyl) phthalate.

The purpose of this study is to determine the inhibitory effect of a glycoprotein isolated from Cudrania tricuspidata Bureau (CTB glycoprotein, 75 kDa) on di(2-ethylhexyl) phthalate (DEHP)-induced differentiation of T helper (Th) type 2 cells in T lymphocytes separated from mice. This experiment evaluated the activities of protein kinase C (PKC), mitogen-activated protein kinase (MAPK), transcription factors [signal transducer and activator of transcription (STAT)-6 and GATA-binding protein 3 (GATA3)], and Th2 cell-related cytokine [interleukin-4 (IL-4)] using immunoblotting and reverse transcription-polymerase chain reaction. Our results revealed that the CTB glycoprotein in the presence of DEHP inhibits the translocation of PKC from cytosol to membrane and the phosphorylation of p44/42 MAPK in primary cultured T lymphocytes. We also found that the CTB glycoprotein (100 microg/ml) has suppressive effects on transcriptional activation of STAT6, GATA3, and on the expression level of IL-4 in DEHP-treated T lymphocytes. The phosphorylation of STAT6 and GATA3 were collectively blocked by treatment with PKC inhibitor (staurosporine) as well as p44/42 MAPK inhibitor (PD 98059), respectively. The results from these experiments indicated that the CTB glycoprotein inhibits IL-4 expression, not IL-10 expression, on the stage of Th2 cell differentiation induced by DEHP in T lymphocytes. Hence, we speculate that the CTB glycoprotein has a strong inhibitory ability for expressions of allergy-related cytokines indirectly caused by DEHP in Th2 cell differentiation of the primary cultured mouse T lymphocytes.