TNF receptor-associated factor (TRAF) proteins are candidate signal transducers that associate with the cytoplasmic domains of members of the tumor necrosis factor (TNF) receptor superfamily. The role of TRAFs in the TNF-R2 and CD40 signal transduction pathways, which result in the activation of transcription factor NF-kappa B, was investigated. Overexpression of TRAF2, but not TRAF1 or TRAF3, was sufficient to induce NF-kappa B activation. A truncated derivative of TRAF2 lacking an amino-terminal RING finger domain was a dominant-negative inhibitor of NF-kappa B activation mediated by TNF-R2 and CD40. Thus, TRAF2 is a common mediator of TNF-R2 and CD40 signaling.

Sepsis in humans is a difficult condition to treat and is often associated with a high mortality rate. In this study, we induced sepsis in rats using cecal ligation and puncture (CLP). In rats depleted of the complement factor C3, CLP led to very short survival times (about 4 days). Of the rats that underwent CLP ('CLP rats') that were C3-intact and treated with preimmune IgG, most (92%) were dead by 7 days. Blood neutrophils from these rats contained on their surfaces the powerful complement activation product C5a. This group had high levels of bacteremia, and their blood neutrophils when stimulated in vitro had greatly reduced production of H2O2, which is known to be essential for the bactericidal function of neutrophils. In contrast, when companion CLP rats were treated with IgG antibody against C5a, survival rates were significantly improved, levels of bacteremia were considerably reduced, and the H2O2 response of blood neutrophils was preserved. Bacterial colony-forming units in spleen and liver were very high in CLP rats treated with preimmune IgG and very low in CLP rats treated with IgG antibody against C5a, similar to values obtained in rats that underwent 'sham' operations (without CLP). These data indicate that sepsis causes an excessive production of C5a, which compromises the bactericidal function of neutrophils. Thus, C5a may be a useful target for the treatment of sepsis.

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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.

In earlier experiments, exogenous administration of secretory leukocyte protease inhibitor (SLPI) suppressed acute lung injury induced by deposition of IgG immune complexes. In the current studies we examined the mechanism of the protective effects of SLPI in this model. The presence of SLPI in the IgG immune complex-model of lung injury reduced the increase in extravascular leakage of 125I-albumin, the intensity of up-regulation of lung vascular intercellular adhesion molecule-1, and the numbers of neutrophils accumulating in the lung. The presence of SLPI caused greatly reduced activation (ie, nuclear translocation) of the transcription nuclear factor-kappaB (NF-kappaB) in lung cells but did not suppress activation of lung mitogen-activated protein kinase. SLPI did not alter NF-kappaB activation in alveolar macrophages harvested 30 minutes after initiation of lung inflammation. In the presence of SLPI, content of tumor necrosis factor-alpha, CXC chemokines, and C5a in bronchoalveolar fluids was unaffected. In the inflamed lungs, inhibition of NF-kappaB activation by SLPI was associated with elevated levels of lung IkappaBbeta (but not IkappaBalpha) protein in the absence of elevated mRNA for IkappaBbeta. When instilled into normal lung, SLPI also caused similar changes (increases) in lung IkappaBbeta. Finally, in the lung inflammatory model used, the presence of anti-SLPI caused accentuated activation of NF-kappaB. These data confirm the anti-inflammatory effect of SLPI in lung and point to a mechanism of anti-inflammatory effects of SLPI. SLPI appears to function as an endogenous regulator of lung inflammation.