Richard W. Erickson

Role of C5a in Multiorgan Failure During Sepsis

In humans with sepsis, the onset of multiorgan failure (MOF), especially involving liver, lungs, and kidneys, is a well known complication that is associated with a high mortality rate. Our previous studies with the cecal ligation/puncture (CLP) model of sepsis in rats have revealed a C5a-induced defect in the respiratory burst of neutrophils. In the current CLP studies, MOF occurred during the first 48 h with development of liver dysfunction and pulmonary dysfunction (falling arterial partial pressure of O2, rising partial pressure of CO2). In this model an early respiratory alkalosis developed, followed by a metabolic acidosis with increased levels of blood lactate. During these events, blood neutrophils lost their chemotactic responsiveness both to C5a and to the bacterial chemotaxin, fMLP. Neutrophil dysfunction was associated with virtually complete loss in binding of C5a, but binding of fMLP remained normal. If CLP animals were treated with anti-C5a, indicators of MOF and lactate acidosis were greatly attenuated. Under the same conditions, C5a binding to blood neutrophils remained intact; in tandem, in vitro chemotactic responses to C5a and fMLP were retained. These data suggest that, in the CLP model of sepsis, treatment with anti-C5a prevents development of MOF and the accompanying onset of blood neutrophil dysfunction. This may explain the protective effects of anti-C5a in the CLP model of sepsis.

Complement-Induced Impairment of Innate Immunity During Sepsis

This study defines the molecular basis for defects in innate immunity involving neutrophils during cecal ligation/puncture (CLP)-induced sepsis in rats. Blood neutrophils from CLP rats demonstrated defective phagocytosis and defective assembly of NADPH oxidase, the latter being due to the inability of p47phox to translocate from the cytosol to the cell membrane of neutrophils after cell stimulation by phorbol ester (PMA). The appearance of these defects was prevented by in vivo blockade of C5a in CLP rats. In vitro exposure of neutrophils to C5a led to reduced surface expression of C5aR and defective assembly of NADPH oxidase, as defined by failure in phosphorylation of p47phox and its translocation to the cell membrane, together with failure in phosphorylation of p42/p44 mitogen-activated protein kinases. These data identify a molecular basis for defective innate immunity involving neutrophils during sepsis.

Induction of gp91-phox, a component of the phagocyte NADPH oxidase, in microglial cells during central nervous system inflammation.

Gp91-phox is an integral component of the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase complex that generates reactive oxygen species (ROS) in activated circulating phagocytes. The authors previously demonstrated that gp91-phox knockout (KO) mice show significant protection from neuronal injury after cerebral ischemia–reperfusion injury, suggesting a pivotal role for this enzyme. Moreover, results from chimeric mice suggested that elimination of gp91-phox from both circulating phagocytes and a putative central nervous system (CNS) source were required to confer neuroprotection. In the current study, the authors demonstrated gp91-phox–specific immunostaining of perivascular cells in the CNS of control rats. However, after transient cerebral ischemia, gp91-phox–positive phagocytes were observed within the core ischemic region and activated microglial cells were positive in the penumbra. Such activated microglial cells were also gp91-phox–positive in the CNS of a chimpanzee with mild meningitis. Finally, in humans, both normal adult CNS tissues and isolated fetal microglial cells expressed gp91-phox mRNA. These microglia also expressed mRNA for the five other known components that comprise the NADPH oxidase complex. These data strongly suggest that microglial cells may contain a functionally active NADPH oxidase capable of generating ROS during CNS inflammation.

The effects of lebrikizumab in patients with mild asthma following whole lung allergen challenge.

Interleukin 13 (IL13) is a T‐helper type 2 (Th2) cytokine associated with inflammation and pathology in allergic diseases such as bronchial asthma. We have shown that treatment with lebrikizumab, an anti‐IL13 monoclonal antibody, significantly improves prebronchodilator forced expiratory volume in 1 s (FEV1) in a subset of subjects with uncontrolled asthma.

The mechanism of activation of NADPH oxidase in the cell-free system: the activation process is primarily catalytic and not through the formation of a stoichiometric complex.

It is commonly assumed that activation of the superoxide-generating NADPH oxidase requires the formation of a stable complex between flavocytochrome b-245 (the gp91phox/p22phox heterodimer) and the cytosolic cofactors p47phox, p67phox and Rac2. This association is thought to convert flavocytochrome b-245, which contains the NADPH-binding site, flavin and haem centres, from an inactive into an active state. Here we provide evidence that, in the cell-free system, this activation process does not necessarily require the formation of a stable stoichiometric complex between the phox proteins. To explain this data we propose the hypothesis that p67phox (and possibly Rac2), are capable of activating flavocytochrome b-245 in a catalytic fashion, where a single molecule of p67phox (or Rac2) is capable of activating multiple flavocytochrome b-245 molecules.