Trauma and aggressive homeostasis management

Natural antibodies bridge innate and adaptive immunity

Natural Abs, belonging to isotypes IgM, IgG3, and IgA, were discovered nearly half a century ago. Despite knowledge about the role of the polyreactive natural IgM in pathogen elimination, B cell survival and homeostasis, inflammatory diseases, and autoimmunity, there is a lack of clarity about the physiological role of natural IgG and natural IgA because they appear incapable of recognizing Ags on their own and are perceived as nonreactive. However, recent research revealed exciting functions of natural IgG in innate immunity. Natural IgG:lectin collaboration swiftly and effectively kills invading pathogens. These advances prompt further examination of natural Abs in immune defense and homeostasis, with the potential for developing novel therapeutics. This review provides new insights into the interaction between natural Abs and lectins, with implications on how interactions between molecules of the innate and adaptive immune systems bridge these two arms of immunity.

Molecular interaction between natural IgG and ficolin--mechanistic insights on adaptive-innate immune crosstalk

Recently, we found that natural IgG (nIgG; a non-specific immunoglobulin of adaptive immunity) is not quiescent, but plays a crucial role in immediate immune defense by collaborating with ficolin (an innate immune protein). However, how the nIgG and ficolin interplay and what factors control the complex formation during infection is unknown. Here, we found that mild acidosis and hypocalcaemia induced by infection- inflammation condition increased the nIgG:ficolin complex formation. Hydrogen-deuterium exchange mass spectrometry delineated the binding interfaces to the CH2-CH3 region of nIgG Fc and P-subdomain of ficolin FBG domain. Infection condition exposes novel binding sites. Site-directed mutagenesis and surface plasmon resonance analyses of peptides, derived from nIgG and ficolin, defined the interacting residues between the proteins. These results provide mechanistic insights on the interaction between two molecules representing the adaptive and innate immune pathways, prompting potential development of immunomodulatory/prophylactic peptides tunable to prevailing infection conditions.

Natural IgG antibodies provide innate protection against ficolin-opsonized bacteria

For nearly five decades since its discovery, the role of natural IgG, which pre-exists in neonates and uninfected individuals, has remained unclear due to the general perception that natural antibodies lack affinity for pathogens. Here, we show for the first time that natural IgG recognizes a spectrum of bacteria through lectins like ficolin and mannose binding lectin (MBL). Infection-inflammation condition markedly increased the affinity of natural IgG for bacteria associated with ficolins. After opsonization with IgG:ficolin complex, the bacteria were phagocytosed by monocytes via FcγRI. Infection of C3(-/-) mice indicated that the natural IgG-mediated immune complex was formed independently of C3. AID(-/-) mice lacking IgG were susceptible to infection, unless reconstituted with natural IgG. Thus, we have proven that natural IgG is not quiescent; rather, it plays a vital and immediate role in immune defense. Our findings provide a fresh perspective on natural antibodies, opening new avenues to explore host-microbe interaction.

Valproic acid reduces autophagy and promotes functional recovery after spinal cord injury in rats

Secondary damage is a critical determinant of the functional outcome in patients with spinal cord injury (SCI), and involves multiple mechanisms of which the most important is the loss of nerve cells mediated by multiple factors. Autophagy can result in cell death, and plays a key role in the development of SCI. It has been recognized that valproic acid (VPA) is neuroprotective in certain experimental animal models, however, the levels of autophagic changes in the process of neuroprotection by VPA treatment following SCI are still unknown. In the present study, we determined the extent of autophagy after VPA treatment in a rat model of SCI. We found that both the mRNA and protein levels of Beclin-1 and LC3 were significantly increased at 1, 2, and 6 h after SCI and peaked at 2 h; however, Western blot showed that autophagy was markedly decreased by VPA treatment at 2 h post-injury. Besides, post-SCI treatment with VPA improved the Basso-Beattie-Bresnahan scale, increased the number of ventral horn motoneurons, and reduced myelin sheath damage compared with vehicle-treated animals at 42 days after SCI. Together, our results demonstrated the characteristics of autophagy expression following SCI, and found that VPA reduced autophagy and enhanced motor function.

Pathophysiological condition changes the conformation of a flexible FBG-related protein, switching it from pathogen-recognition to host-interaction

Although homeostatic disturbance of the blood pH and calcium in the vicinity of tissue injury/malignancy/local infection seems subtle, it can cause substantial pathophysiological consequences, a phenomenon which has remained largely unexplored. The fibrinogen-related proteins (FREPs) containing fibrinogen-like domain (FBG) represent a conserved protein family with a common calcium-binding region, implying the presence of elements responsive to physiological perturbation. Here, we studied the molecular interaction between a representative FREP, the M-ficolin, and an acute phase blood protein, the C-reactive protein (CRP), both of which are known to trigger and control seminal pathways in infection and injury. Using hydrogen-deuterium exchange mass spectrometry, we showed that the C-terminal region of M-ficolin FBG underwent dramatic conformational change upon pH and calcium perturbations. Biochemical and biophysical assays showed that under defined pathophysiological condition (pH 6.5, 2.0 mM calcium), the FBG:CRP interaction occurred more strongly compared to that under physiological condition (pH 7.4, 2.5 mM calcium). We identified the binding interface between CRP and FBG, locating it to the pH- and calcium-sensitive C-terminal region of FBG. By site-directed mutagenesis, we determined H284 in the N-acetylglucosamine (GlcNAc)-binding pocket of the FBG, to be the critical CRP-binding residue. This conformational switch involving H284, explains how the pathophysiologically-driven FBG:CRP interaction diverts the M-ficolin away from GlcNAc/pathogen-recognition to host protein-protein interaction, thus enabling the host to regain homeostatic control. Our elucidation of the binding interface at the flexible FBG domain provides insights into the bioactive centre of the M-ficolin, and possibly other FREPs, which might aid future development of immunomodulators.

Local inflammation induces complement crosstalk which amplifies the antimicrobial response

By eliciting inflammatory responses, the human immunosurveillance system notably combats invading pathogens, during which acute phase proteins (CRP and cytokines) are elevated markedly. However, the Pseudomonas aeruginosa is a persistent opportunistic pathogen prevalent at the site of local inflammation, and its acquisition of multiple antibiotic-resistance factors poses grave challenges to patient healthcare management. Using blood samples from infected patients, we demonstrate that P. aeruginosa is effectively killed in the plasma under defined local infection-inflammation condition, where slight acidosis and reduced calcium levels (pH 6.5, 2 mM calcium) typically prevail. We showed that this powerful antimicrobial activity is provoked by crosstalk between two plasma proteins; CRPratioL-ficolin interaction led to communication between the complement classical and lectin pathways from which two amplification events emerged. Assays for C4 deposition, phagocytosis, and protein competition consistently proved the functional significance of the amplification pathways in boosting complement-mediated antimicrobial activity. The infection-inflammation condition induced a 100-fold increase in CRPratioL-ficolin interaction in a pH- and calcium-sensitive manner. We conclude that the infection-induced local inflammatory conditions trigger a strong interaction between CRPratioL-ficolin, eliciting complement-amplification pathways which are autonomous and which co-exist with and reinforce the classical and lectin pathways. Our findings provide new insights into the host immune response to P. aeruginosa infection under pathological conditions and the potential development of new therapeutic strategies against bacterial infection.

Independent determinants of early death in critically ill surgical patients

Abnormalities in cardiocirculatory, respiratory, or coagulatory parameters are frequent after major surgery, but so far, no study has investigated their predictive value for early intensive care unit (ICU) mortality. We aimed to describe and quantify the relation between these parameters that are routinely determined on ICU admission and early death after complex surgery. Individual patient data were available from a local ICU database. We performed a retrospective observational cohort study using prospectively collected data from March 1, 1993, through February 28, 2005. A cohort of 4,214 cases who were admitted to the ICU immediately after operation was analyzed. We studied age, sex, number of red blood cell units transfused on admission day, and admission values for heart rate, systolic blood pressure, hemoglobin concentration, partial thromboplastin time, prothrombin time, respiratory function (Pao2/Fio2 ratio), and body temperature for their association with 4-day mortality. Effects were adjusted for the underlying disease and for disease severity during the first 24 h after admission. We used generalized additive models to fit continuous variables individually before combining them into the final generalized model. We found an independent linear association between the number of transfused red blood cell units, partial thromboplastin time, and body temperature with acute outcome. A smoothed model described the independent interaction between admission blood pressure and early death. Only values of less than 80 mmHg were associated with an increased risk of 4-day mortality. According to these results, bleeding complications after ICU admission should be treated aggressively to prevent early death of the patient. However, normotensive conditions do not seem to be required to prevent early mortality. Whether rapid rewarming may improve outcome needs further rigorous study.