Phagocytosis of bacteria and production of intracellular reactive oxygen components and hydrolyzing enzymes such as proteases that may be released in the extracellular milieu upon activation. Recently, the formation of neutrophil extracellular traps, a mechanism that allows neutrophils to retain antimicrobial activity after death, has been identified as an additional mechanism and alternative for death by necrosis or apoptosis. A side effect of these efficient antimicrobial mechanisms and release of highly active molecules and hydrolyzing enzymes is partial tissue destruction. To provide the rapid and adequate immune response that is restricted in time to the duration of the infection and to avoid chronic inflammation, precise control of local neutrophil accumulation and activation is essential. One of the mechanisms that regulate neutrophil recruitment and activation is enzyme-induced posttranslational modification of ELR+ CXC chemokines. In fact, the ELR+ CXC chemokine CXCL7 only becomes activated upon proteolytic removal of a large part of the NH2-terminal region. For other ELR+ CXC chemokines the activity has been reported to be up-regulated upon limited truncation of the NH2- terminus by specific enzymes such as plasmin, thrombin, matrix metalloproteases, etc. However, further truncation within the ELR motif results in almost complete inactivation of all ELR+ CXC chemokines. Numerous posttranslationally modified natural forms of the different ELR+ CXC chemokines have been identified and partially characterized. Leukocyte-derived conditioned medium contains at least 10 different truncated and also citrullinated forms of the most potent human ELR+ CXC chemokine, CXCL8. Incubation of CXCL8 with the myeloid aminopeptidase CD13 results in the removal of one or two amino acids from the 77 amino acid CXCL8. The Arg in position 5 is a crucial amino acid for cleavage of CXCL8 into CXCL8 by the serine proteases plasmin and thrombin. CXCL8 truncated by five to eight NH2-terminal residues, becomes a three- to ten-fold more potent neutrophil attractant and angiogenic molecule in vitro and in vivo. Citrullination of natural CXCL8 by peptidylarginine deiminase -2 or PAD-4 also occurs specifically on Arg in position 5. Citrullination significantly reduces the capacity of CXCL8 to induce neutrophil extravasation without affecting its angiogenic activity. However, intravenously injected citrullinated CXCL8 is a more potent mobilizer of mature neutrophils to the blood stream. In addition to proteolytic truncation and citrullination, alternative cleavage of the signal peptide results in a natural CXCL8 form with two extra NH2-terminal amino acids, i.e. CXCL8 containing 79 amino acids or CXCL8. Significant amounts of natural elongated CXCL8 and truncated CXCL8 and CXCL8 have been reported to be produced by lymphocytes, monocytes and fibroblasts. Since these forms co-elute on chromatographic GSK1363089 columns with other CXCL8 forms the individual forms were not readily available as pure proteins for the evaluation of their biological activity. Here we produced the different CXCL8 forms by Fmoc solid phase peptide synthesis.