The unique structural and functional features of CXCL12

The CXC chemokine CXCL12 is an important factor in physiological and pathological processes, includingembryogenesis, hematopoiesis, angiogenesis and inflammation, because it activates and/or induces migration ofhematopoietic progenitor and stem cells, endothelial cells and most leukocytes. Therefore, CXCL12 activity istightly regulated at multiple levels. CXCL12 has the unique property of existing in six splice variants in humans,each having a specific tissue distribution and in vivo activity. Controlled splice variant transcription and mRNAstability determine the CXCL12 expression profile. CXCL12 fulfills its functions in homeostatic and pathologicalconditions by interacting with its receptors CXC chemokine receptor 4 (CXCR4) and atypical chemokine receptor 3(ACKR3) and by binding to glycosaminoglycans (GAGs) in tissues and on the endothelium to allow a properpresentation to passing leukocytes. Homodimerizaton and heterodimerization of CXCL12 and its receptors can altertheir signaling activity, as exemplified by the synergy between CXCL12 and other chemokines in leukocyte migrationassays. Receptor binding may also initiate CXCL12 internalization and its subsequent removal from theenvironment. Furthermore, CXCL12 activity is regulated by posttranslational modifications. Proteolytic removal ofNH2- or COOH-terminal amino acids, citrullination of arginine residues by peptidyl arginine deiminases or nitrationof tyrosine residues reduce CXCL12 activity. This review summarizes the interactions of CXCL12 with the cellularenvironment and discusses the different levels of CXCL12 activity regulation.

Chemoattractants and cytokines in primary ciliary dyskinesia and cystic fibrosis: key players in chronic respiratory diseases

Patients with primary ciliary dyskinesia(PCD)and cystic fibrosis(CF),two inherited disorders,suffer from recurrent airway infections characterized by persistent bacterial colonization and uncontrollable inflammation.Although present in high counts,neutrophils fail to clear infection in the airways.High levels of C-X-C motif chemokine ligand 8/interleukin-8(CXCL8/IL-8),the most potent chemokine to attract neutrophils to sites of infection,are detected in the sputum of both patient groups and might cause the high neutrophil influx in the airways.Furthermore,in CF,airway neutrophils are highly activated because of the genetic defect and the high levels of proinflammatory chemoattractants and cytokines(e.g.,CXCL8/IL-8,tumor necrosis factor-αand IL-17).The overactive state of neutrophils leads to lung damage and fuels the vicious circle of infection,excessive inflammation and tissue damage.The inflammatory process in CF airways is well characterized,whereas the lung pathology in PCD is far less studied.The knowledge of CF lung pathology could be useful to guide molecular investigations of the inflammatory processes in PCD lungs.Current available therapies can not completely remedy the chronic airway infections in these diseases.This review gives an overview of the role that chemoattractants and cytokines play in these neutrophil-dominated lung pathologies.Finally,the most frequently applied treatments in CF and PCD and new experimental therapies to reduce neutrophil-dominated airway inflammation are described.