These findings suggest that the presence of high levels of functionally active TREM-1 in RA synovium may contribute to the development or maintenance of RA, or both. Inhibiting TREM-1 activity may, therefore, have a therapeutic effect on RA. High levels of soluble TREM-1 in the plasma of RA patients compared with healthy volunteers may indicate disease activity.

Tumor necrosis factor ␣ (TNF␣) is a pro-inflammatory cytokine that controls the initiation and progression of inflammatory diseases such as rheumatoid arthritis. Tpl2 is a MAPKKK in the MAPK (i.e. ERK) pathway, and the Tpl2-MEK-ERK signaling pathway is activated by the pro-inflammatory mediators TNF␣, interleukin (IL)-1␤, and bacterial endotoxin (lipopolysaccharide (LPS)). Moreover, Tpl2 is required for TNF␣ expression. Thus, pharmacologic inhibition of Tpl2 should be a valid approach to therapeutic intervention in the pathogenesis of rheumatoid arthritis and other inflammatory diseases in humans. We have developed a series of highly selective and potent Tpl2 inhibitors, and in the present study we have used these inhibitors to demonstrate that the catalytic activity of Tpl2 is required for the LPS-induced activation of MEK and ERK in primary human monocytes. These inhibitors selectively target Tpl2 in these cells, and they block LPS-and IL-1␤-induced TNF␣ production in both primary human monocytes and human blood. In rheumatoid arthritis fibroblast-like synoviocytes these inhibitors block ERK activation, cyclooxygenase-2 expression, and the production of IL-6, IL-8, and prostaglandin E 2 , and the matrix metalloproteinases MMP-1 and MMP-3. Taken together, our results show that inhibition of Tpl2 in primary human cell types can decrease the production of TNF␣ and other pro-inflammatory mediators during inflammatory events, and they further support the notion that Tpl2 is an appropriate therapeutic target for rheumatoid arthritis and other human inflammatory diseases.

Adenoviral delivery of genes to primary bovine chondrocytes, followed by culture in three-dimensional pellet format and evaluation of extracellular matrix protein metabolism, is a useful functional assay for assessing the role of genes on cartilage matrix synthesis and degradation.

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