A Fab fragment of a recombinant, humanized monoclonal antibody directed against the proinflammatory cytokine tumor necrosis factor-alpha (TNF-alpha), with anti-inflammatory activity. Upon administration, certolizumab binds to TNF-alpha, preventing the interaction of this cytokine with endogenous cell surface receptors, thereby rendering TNF-alpha inactive and inhibiting TNF-mediated inflammatory responses. TNF-alpha is a protein involved in inflammation, cell survival, and apoptosis.