Stroke alters respiratory burst in neutrophils and monocytes

Stroke-induced immune alterations predispose patients to infections. Although the relationship between stroke and the adaptive immune system has been investigated in detail, to date it is unknown whether the innate immune system, which forms the first line of antibacterial defense, is also impaired in patients with stroke. Therefore, we investigated whether chemotaxis, phagocytosis, oxidative burst, degranulation of defensins, and NETosis in monocytes and in neutrophil granulocytes are altered in patients with stroke compared with controls.

Sixty-three patients having acute ischemic stroke were recruited within 12 hours of symptom onset; blood was sampled on admission and on days 1, 3, 5, and 7. Thirty-seven age-matched controls were also recruited. Cell migration, phagocytosis, and oxidative burst of phagocytes were determined in vitro. Human neutrophil peptides 1 to 3 and serum metanephrine levels were measured by enzyme-linked immunosorbent assay, and NETosis was quantified by immunohistochemistry.

The key mechanisms required for bacterial killing, oxidative burst, and NETosis were significantly reduced in samples taken from patients with stroke compared with controls, whereas migration, phagocytic function, and defensin production remained unimpaired in monocytes and granulocytes from patients with stroke.

Stroke-induced immune alterations include impairment of the first-line defense performed by specialized phagocytes against bacteria. The hypothesis that these changes enhance susceptibility to acquired infections is supported by our observation that on admission oxidative burst in monocytes was more impaired in patients with stroke with subsequent stroke-associated infections.