Hypochlorous acid (HOCl) is produced in the human body by the family of mammalian heme peroxidases, mainly by myeloperoxidase, which is secreted by neutrophils and monocytes at sites of inflammation. This review discusses the reactions that occur between HOCl and the major classes of biologically important molecules (amino acids, proteins, nucleotides, nucleic acids, carbohydrates, lipids, and inorganic substances) to form free radicals. The generation of such free radical intermediates by HOCl and other reactive halogen species is accompanied by the development of halogenative stress, which causes a number of socially important diseases, such as cardiovascular, neurodegenerative, infectious, and other diseases usually associated with inflammatory response and characterized by the appearance of biomarkers of myeloperoxidase and halogenative stress. Investigations aimed at elucidating the mechanisms regulating the activity of enzyme systems that are responsible for the production of reactive halogen species are a crucial step in opening possibilities for control of the development of the body's inflammatory response.

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IntroductionTwo major responses are central to neutrophil leukocyte (polymorphonuclear neutrophil [PMN]) functioning: chemotaxis and phagocytosis. The migration of leukocytes is governed by chemotactic cytokines called chemokines. Chemokines are a large family of small chemotactic proteins divided into 4 subfamilies according to the positioning of cysteines in their primary sequences. Those whose first 2 cysteines are separated by one amino acid belong to the CXC (or ␣) subfamily and regulate the responses of PMNs. 1,2 Human CXC chemokines interact with the specific G-proteincoupled receptors CXCR1 and CXCR2. CXCR1 has high affinity for interleukin-8 (IL-8) and low affinity for other ␣-chemokines, neutrophil-activating peptide-2 (NAP-2), melanoma growthstimulatory activity (growth-regulated oncogene), and others, whereas CXCR2 shows a high affinity for all CXC chemokines that contain an N-terminal Glu-Leu-Arg motif. 3 Because it has long been shown that after phagocytosis the chemotactic responses of neutrophils are impaired, 4 we investigated the effect of phagocytic stimulation of human neutrophils on the expression of IL-8 receptors CXCR1 and CXCR2. Study design NeutrophilsNeutrophils were isolated from heparinized blood of healthy volunteers by dextran sedimentation of erythrocytes followed by centrifugation on Lymphoprep (Nycomed, Oslo, Norway) and lysis of residual erythrocytes with distilled water. 5,6 Approval was obtained from the institutional review board at the Institute of Hematology and Blood Transfusion, Minsk, Belarus, for these studies. Informed volunteer consent was obtained according to the Declaration of Helsinki. Neutrophils were 95% to 96% pure and more than 98% viable. Purified neutrophils were incubated at 37°C in RPMI containing 2% fetal calf serum (Hyclone, Logan, UT) at 2 to 3 ϫ 10 6 cells per milliliter in polypropylene tubes (Corning, NY) as described. 6 The cells were stimulated with heat-killed and opsonized 7 Saccharomyces cerevisiae (OSC; OSC/PMN ratio, 2:1), opsonized sheep red blood cells (SRBCs; 5:1), or opsonized zymosan particles (30 mg/mL; Sigma, St Louis, MO). All reagents and solutions were controlled for endotoxin contamination by means of Limulus amebocyte assay (E-toxate; Sigma). Phagocytic activity of PMNs was determined as described previously 8 in cell smears by means of Wright stain (Accustain; Sigma). Flow cytometry analysisNeutrophils were stained as described 6 with the use of our mouse monoclonal antibody (mAb) 6 E3 recognizing N-terminal amino acids 10 through 12 (Trp-Asp-Phe) of human CXCR1, mAb R115 to CXCR2, 9 kindly provided by Dr Ernst Brandt (Forschungszentrum, Borstel, Germany), mAb to receptor for complement fragment C5a (C5aR, CD88 10 ; all mAbs were immunoglobulin G1 [IgG1]), kindly donated by Prof Otto Goetze (Georg-August-University, Goettingen, Germany), or isotype control mAb and were analyzed by FACScan (Becton Dickinson, Mountain View, CA) by means of Lysis II software (Becton Dickinson). Confocal microscopySmears were fixed in acetone, permeab...