Methotrexate inhibits LPS-induced tumor necrosis factor production in vivo

We investigated the effects of methotrexate (MTX) on the production of tumor necrosis factor (TNF), nitric oxide (NO) and interleukin-10 (IL-10) in vivo. Administration of low doses of MTX (450 mug/kg once a week for 4 weeks) in Balb/c mice resulted in a significant inhibition of the systemic release of TNF and NO upon LPS challenge, whereas the production of IL-10 remained unchanged. These anti-inflammatory effects of MTX were exerted at the macrophage level since peritoneal macrophages from mice, injected for 4 weeks with MTX produced lower levels of TNF than cells from control mice upon LPS stimulation ex vivo. In parallel, we found that MTX-treated mice were less susceptible to a lethal challenge with LPS and D-galactosamine. MTX did not inhibit TNF release after injection of Concanavalin A (ConA) or anti-CD3 monoclonal antibody (mAb), indicating that MTX does not inhibit TNF production at the T cell level. We conclude that repeated administration of a low dose of MTX in mice is associated with a decreased production of TNF by macrophages upon LPS activation.