According to product labeling, Infliximab neutralizes the biological activity of TNFα by binding with high affinity to the soluble (free floating in the blood) and transmembrane (located on the outer membranes of T cells and similar immune cells) forms of TNFα and inhibits or prevents the effective binding of TNFα with its receptors. Infliximab (Remicade) and Humira (another TNF antagonist) are in the subclass of "anti-TNF antibodies" (they are in the form of naturally occurring antibodies), and are capable of neutralizing all forms (extracellular, transmembrane, and receptor-bound) of TNF alpha. Enbrel, a third TNF antagonist, is in a different subclass (receptor-construct fusion protein), and, because of its modified form, cannot neutralize receptor-bound TNFa. Additionally, the anti-TNF antibodies Humira and infliximab (Remicade) have the capability of lysing cells involved in the inflammatory process, whereas the receptor fusion protein apparently lacks this capability. Although the clinical significance of these differences have not been absolutely proven, they may account for the differential actions of these drugs in both efficacy and side effects.
Infliximab has high specificity for TNFα, and does not neutralize TNF beta (TNFβ, also called lymphotoxin α), an unrelated cytokine that uses different receptors from TNFα. Biological activities that are attributed to TNFα include: induction of proinflammatory cytokines such as interleukin (IL) 1 and IL 6, enhancement of leukocyte movement or migration from the blood vessels into the tissues by increasing the permeability of endothelial layer of blood vessels; and increasing the release of adhesion molecules. Infliximab prevents disease in transgenic mice (a special type of mice that are biologically engineered to produce a human form of TNFα and which are used to test the results of these drugs that might be expected in humans). These experimental mice develop arthritis as a result of their production of human TNFα, and when administered after disease onset, infliximab allows eroded joints to heal.
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