Seby John, MD
Ruhnau J, Schulze K, Gaida B, Langner S, Kessler C, Bröker B, et al. Stroke Alters Respiratory Burst in Neutrophils and Monocytes. Stroke. 2014

Infections can cause stroke, and stroke increases the rate of infections. In fact, infection is the most common complication after stroke and contributes to poor functional outcome. Pneumonia for instance occurs in upto 22% of patients and is the leading cause of death after stroke. This bidirectional relationship is complex. Recall the parts of the immune system, it comprises the innate and adaptive immune systems, each differing with respect to how quickly and for how long it responds, central effector cell types and its specificity for pathogens. The association between the adaptive system and stroke has been well investigated, but the function of the innate system in stroke is unknown.

Ruhnau and colleagues studied functions of the innate immune system in patients with acute ischemic stroke. They found that migration, phagocytic function, and defensin production of the monocytes and granulocytes remained intact. However, key bactericidal mechanisms such as oxidative burst and NETosis were significantly reduced in acute stroke patients compared to healthy controls. Furthermore, admission oxidative burst of monocytes were more impaired in stroke patients who later went on to develop severe systemic infections. Despite the limitations of in vitro testing, the authors hypothesize that decreased bactericidal function is causally related to the increased risk of developing infections after stroke.

Factors such as aspiration, crural weakness, bedridden state, urinary incontinence etc. alone cannot entirely explain the increased risk of infection. Immunodeficiency of the innate and adaptive systems in addition offers a better explanation. This raises the question of short-term prophylactic antibiotics. The ESPIAS and PANTHERIS trials that studied this question found no benefit in outcomes, but may have been related to fluroquinolone neurotoxicity. In contrast, studies where minocycline, and mezlocillin/sulbactam (Mannheim Infection in Stroke Study) prophylaxis was used showed improved clinical outcomes. Lets hope that further knowledge of the immune system in stroke may aid in optimally selecting an antimicrobial regimen for prophylaxis, that can be tested in future trials.