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Human Neutrophil Peptides and Phagocytic Deficiency in Bronchiectatic Lungs

¹ The Keenan Research Centre in the Li Ka Shing Knowledge Institute of St. Michael's Hospital, Toronto, Ontario, Canada; ² Department of Anaesthesia, ³ Department of Physiology, ⁴ Interdepartmental Division of Critical Care Medicine, and ⁵ Division of Respiratory Medicine, University of Toronto, Toronto, Canada; ⁶ Department of Medicine, Centre Hospitalier Universitaire de Sherbrooke, Quebec, Canada; and ⁷ Integrated Department of Immunology, National Jewish Health, Denver, Colorado

Correspondence and requests for reprints should be addressed to Haibo Zhang, M.D., Ph.D., Room 7-007, Queen Wing 30 Bond Street, Toronto, Ontario M5B 1W8, Canada. E-mail: zhangh{at}smh.toronto.on.ca

Rationale: A well-known clinical paradox is that severe bacterial infections persist in the lungs of patients with cystic fibrosis (CF) despite the abundance of polymorphonuclear neutrophils (PMN) and the presence of a high concentration of human neutrophil peptides (HNP), both of which are expected to kill the bacteria but fail to do so. The mechanisms remain unknown.

Objectives: This study examined several possible mechanisms to understand this paradox.

Methods: PMN were isolated from sputum and blood of subjects with and without CF or non-CF bronchiectasis for phagocytic assays. HNP isolated from patients with CF were used to stimulate healthy PMN followed by phagocytic tests.

Measurements and Main Results: PMN isolated from the sputum of the bronchiectatic patients display defective phagocytosis that correlated with high concentrations of HNP in the lung. When healthy PMN were incubated with HNP, decreased phagocytic capacity was observed in association with depressed surface Fc RIII, actin-filament remodeling, enhanced intracellular Ca²⁺, and degranulation. Treatment of PMN with an intracellular Ca²⁺ blocker or 1-proteinase inhibitor to attenuate the activity of HNP largely prevented the HNP-induced phagocytic deficiency. Intratracheal instillation of HNP in Pallid mice (genetically deficient in 1-proteinase inhibitor) resulted in a greater PMN lung infiltration and phagocytic deficiency compared with wild-type mice.

Conclusions: HNP or PMN alone exert antimicrobial ability, which was lost as a result of their interaction. These effects of HNP may help explain the clinical paradox seen in patients with inflammatory lung diseases, suggesting HNP as a novel target for clinical therapy.

Key Words: inflammation • innate immunity • lung injury

AT A GLANCE COMMENTARY Scientific Knowledge on the Subject Severe bacterial infections persist in bronchiectatic lungs despite the abundance of neutrophils and the presence of human neutrophil peptides (HNP), both of which are expected to kill the bacteria but fail to do so. The mechanisms remain unknown. What This Study Adds to the Field HNP or neutrophils alone exert antimicrobial ability, which was lost as a result of their interaction. This finding may explain the clinical paradox and suggests HNP as a novel target for clinical therapy in inflammatory diseases.