Compositions and methods are disclosed for inhibiting the release of a proinflammatory cytokine from a vertebrate cell, and for inhibiting an inflammatory cytokine cascade in a patient. The compositions comprise a vertebrate HMGB A box, and an antibody preparation that specifically binds to a vertebrate HMGB B box. The methods comprise treating a cell or a patient with sufficient amounts of the composition to inhibit the release of the proinflammatory cytokine, or to inhibit the inflammatory cytokine cascade.