ANTAGONISM BY IL-4 AND IL-10 OF ENDOTOXIN-INDUCED TISSUE FACTOR ACTIVATION IN MONOCYTIC THP-1 CELLS - ACTIVATING ROLE OF CD14 LIGATION

Background. Monocytic tissue factor (TF), initiating the extrinsic blo od coagulation pathway, is often upregulated under septic or inflammat ory conditions. The complex activating mechanism remains largely uncle ar and no effective strategy has been firmly established. In this stud y, we? used a model monocytic cell line (human leukemic THP-1 promonoc ytes) to address (1) the nature of TF activation in response to bacter ial endotoxin and (2) the application of antiinflammatory cytokines in relieving monocytic hypercoagulation. Results. TF in THP-1 cells was substantially activated by exposure to bacterial endotoxin (LPS; 5 mu g/ml) for 6 h. Human recombinant IL-4 (500 ng/ml) and IL-10 (500 ng/ml ) inhibited TF activation induced by LPS. To determine if these cytoki nes depressed LPS recognition resulting in such inhibition, we employe d an anti-CD14 mAb (UCHM-1; Sigma Chemical) to address the role of CD1 4 in LPS transmembrane signaling. LPS-induced TF activation was depres sed by 35% upon inclusion of the anti-CD14 mAb (1:10 dilution). This a ntibody alone mimicked TF activation which accounted for 35% of the LP S-induced TF activation, suggesting the activating role of CD14 ligati on. In addition, the anti-CD14 mAb elicited the production of nitric o xide (NO) which was found to be independent of TF activation. NO produ ction could serve as an independent index for monitoring LPS recogniti on. IL-4 depressed the anti-CD14 mAb-induced TF activation as well as NO elicitation, indicating the blockade of CD14 ligation. In contrast, IL-10 showed differential inhibitory activities. TF activation induce d by either LPS or anti-CD14 mAb was inhibited by IL-10 which did not show any inhibition on NO elicitation under these conditions. In a sep arate approach, neither IL-4 nor IL-10 inhibited phorbol ester-induced NO elicitation, More direct evidence came from an epifluorescent demo nstration showing that IL-4 blocked binding of FITC-conjugated LPS and anti-CD14 mAb to THP-1 cells. Conclusions. Taken together, the result s suggest that LPS action in relation to TF activation consists of CD1 4-independent and -dependent signaling including CD14 ligation. We als o showed that antiinflammatory cytokines (IL-4 and -10) significantly depressed TF activation. IL-4 antagonized CD14-dependent LPS recogniti on leading to the depression in TF activation. (C) 1998 Academic Press .