Infliximab and the TNF-alpha system.

Infliximab, a chimeric monoclonal antibody against TNF-alpha, is efficacious in Crohn's disease (CD) and rheumatoid arthritis (RA). Its main mechanism of action is thought to be the induction of apoptosis. The present study evaluates in detail the effects of infliximab on the TNF-alpha system using peripheral blood monocytes and T cells as well as lamina propria lymphocytes from normal individuals and patients with CD, ulcerative colitis, and RA. Lymphocytes were studied in the resting state in the absence of strong stimuli that may obscure subtle findings. Infliximab did not change the numbers of viable cells. Rather, it caused monocytes to increase their release of soluble TNFR2, which serves to neutralize TNF-alpha, potentiating the action of infliximab. It reduced TNFR2 expression, thereby decreasing TNF-alpha responsiveness. These changes were due to upregulated production of TNFR2 rather than increased shedding. Infliximab did not cause rebound production of TNF-alpha transcripts that would counteract its effects. It specifically enhanced production of IL-10 but not proinflammatory cytokines secreted by leukocytes, thereby promoting an anti-inflammatory microenvironment. In addition, infliximab caused a rise in c-Jun amino-terminal kinase phosphorylation by monocytes. Thus infliximab manipulates the TNF-alpha system to promote its anti-TNF-alpha effects.