<prompt> All of the following are mediators of acute inflammation exceptTumor necrosis factor _alfaIL1MyeloperoxidaseProstaglandins  <response>: ref Robbins 9e p83 Myeloperoxidase MPO is a heme-containing enzyme that, in the presence of peroxide and halide ions, is effective in killing various microorganisms; in addition, it exes a wide variety of extracellular functions. Polymorphonuclear leukocytes PMN are the main source of this enzyme. 