Among the Sp transcription fac tors, Sp1 has been extensively studied and is known to be widely only expressed and to play a role in the regulation of a vast array of genes. Thus, while not excluding a role for other nuclear factors our data confirm previous studies showing that IL 10 gene expression is controlled by the transcription factor Sp1 since mithramycin, an inhibitor of Sp1, almost completely abrogated LPS induced IL 10 production at the mRNA and protein level. EMSA assay confirmed this observation as it showed that mithramycin decreased the activation of the nuclear pro tein Sp1 after LPS stimulation. Transfection of HAM by antisense oligonucleotides to Sp1 could not be used as another approach to confirm the role of Sp1 in IL 10 induction by LPS, as after the time period required to silence Sp1 expression following 4 hrs transfection, HAMs were not anymore responsive to LPS for IL 10 production.
Interestingly, inhibition of MAPKs by their specific inhibitors, also abolished LPS induced Sp1 activation. These results are in accordance with previous studies showing that Sp1 phosphorylation can be induced by ERK and p38 MAP kinases. In addition the present study also showed that JNK MAP kinase is also required for the activation of Sp1 induced by LPS. The three MAP kinases seem however to have different contributions to LPS induced IL 10 in HAM, with a prominent role of p38 and ERK. IL 10 production by alveolar macrophages has been debated since some authors described the inability of alveolar macrophages to produce IL 10.
Other investigators related this to a reduced production of IL 10 to allergic inflammation. Our data clearly confirm IL 10 production by normal HAM, provide new information on the mechanisms involved in this produc tion and complete the studies of Boehringer et al who has studied the role of PP1 and PP2A in the regulation of LPS induced IL 10 in HAM. Conclusion Our study demonstrates the contribution of MAP kinases to IL 10 expression in HAM upon endotoxin activation, indicating that ERK and p38 and to a lesser extent JNK are involved. In addition we show that ERK, p38 and JNK are able to trigger the phosphorylation of Sp1, the major tran scription factor for the IL 10 gene. These findings are highly relevant to lung immunity, alveolar macrophages assuming front line defense mechanisms and IL 10 repre senting a key factor for mucosal tolerance and resolution of inflammatory responses.
Background Acute lung injury and acute respiratory distress syndrome are well defined and readily recog nised clinical disorders caused by many clinical insults to the lung or because of predispositions to lung injury. Sepsis and pneumonia are the main causes of Batimastat ALI clinically. ALI occurring during gram negative bacterial pneumonia and sepsis is caused in large part by lipo polysaccharide, a component of the cell walls of gram negative bacteria.