Complement in human diseases: looking towards the 21st century

Meta-analysis of the effect of peritoneal lavage on survival in experimental peritonitis

Background

Morbidity and mortality associated with bacterial peritonitis remain a challenge for contemporary surgery. Despite great surgical improvements, death rates have not improved. A secondary debate concerns the volume and nature of peritoneal lavage or washout—what volume, what carrier and what, if any, antibiotic or antiseptic?

Methods

A literature search of experimental studies assessing the effect of peritoneal lavage following peritonitis was conducted using Medline, EMBASE and Cochrane databases. Twenty-three trials met predetermined inclusion criteria. Data were pooled and relative risks calculated.

Results

In an experimental peritonitis setting a mortality rate of 48·9 per cent (238 of 487) was found for saline lavage compared with 16·4 per cent (106 of 647) for antibiotic lavage (absolute risk reduction (ARR) 32·5 (95 per cent confidence interval (c.i.) 27·1 to 37·7) per cent; (P < 0·001). An ARR of 25·0 (95 per cent c.i. 17·9 to 31·7) per cent P < 0·001) was found for the use of saline compared with no lavage at all. The survival benefit persisted regardless of systemic antibiotic therapy. Antiseptic lavage was associated with a very high mortality rate (75·0 per cent).

Conclusion

Pooled data from studies in experimental peritonitis demonstrated a significant reduction in mortality with antibiotic lavage.

Localized-statistical quantification of human serum proteome associated with type 2 diabetes

BACKGROUND

Recent advances in proteomics have shed light to discover serum proteins or peptides as biomarkers for tracking the progression of diabetes as well as understanding molecular mechanisms of the disease.

RESULTS

In this work, human serum of non-diabetic and diabetic cohorts was analyzed by proteomic approach. To analyze total 1377 high-confident serum-proteins, we developed a computing strategy called localized statistics of protein abundance distribution (LSPAD) to calculate a significant bias of a particular protein-abundance between these two cohorts. As a result, 68 proteins were found significantly over-represented in the diabetic serum (p<0.01). In addition, a pathway-associated analysis was developed to obtain the overall pathway bias associated with type 2 diabetes, from which the significant over-representation of complement system associated with type 2 diabetes was uncovered. Moreover, an up-stream activator of complement pathway, ficolin-3, was observed over-represented in the serum of type 2 diabetic patients, which was further validated with statistic significance (p = 0.012) with more clinical samples.

CONCLUSIONS

The developed LSPAD approach is well fit for analyzing proteomic data derived from biological complex systems such as plasma proteome. With LSPAD, we disclosed the comprehensive distribution of the proteins associated with diabetes in different abundance levels and the involvement of ficolin-related complement activation in diabetes.

Immunology

The concept of forbidden foods that should not be eaten goes back to the Garden of Eden and apart from its religious meanings it may also have foreshadowed the concept of foods that can provoke adverse reactions. Thus we could say that allergic diseases have plagued mankind since the beginning of life on earth. The prophet Job was affected by a condition that following the rare symptoms described by the Holy Bible might be identified as a severe form of atopic dermatitis (AD). The earliest record of an apparently allergic reaction is 2621 B.C., when death from stinging insects was first described by hieroglyphics carved into the walls of the tomb of Pharaoh Menes depicting his death following the sting of a wasp. In 79 A.D., the death of the Roman admiral Pliny the Elder was ascribed to the SO₂-rich gases emanating from the eruption of Mount Vesuvius. Hippocrates (460–377 B.C.) was probably the first to describe how cow’s milk (CM) could cause gastric upset and hives, proposing dietetic measures including both treatment and prevention for CM allergy.

Identification of alternative pathway serum complement activity in the blood of the American alligator (Alligator mississippiensis)

Incubation of different dilutions of alligator serum with sheep red blood cells (SRBCs) that had not been sensitized with antibodies resulted in concentration-dependent hemolytic activity. This hemolytic activity was not affected by the presence of ammonium hydroxide and methylamine, known inactivators of the classical complement cascade. However, the hemolytic activities were inhibited by EDTA and salicylaldoxime, indicating that the alternate pathway is primarily responsible for these activities. Immunofixation of electrophoretically-resolved alligator serum proteins with antihuman C3 polyclonal antibodies resulted in detection of a protein antigenically similar to human C3 in alligator serum. SDS-PAGE, followed by Western blot analysis, revealed the presence of two alligator serum proteins with nearly identical molecular weights as human C3alpha and C3beta. SRBC hemolysis and antibacterial activity by alligator serum was significantly reduced in the presence of antihuman C3 antibodies. The hemolytic effect of alligator serum was shown to occur rapidly, with significant activity within 5 min and maximal activity occurring at 15 min. SRBC hemolysis was also temperature-dependent, with reduced activity below 15 degrees C and above 30 degrees C. These data suggest that the antibiotic properties of alligator serum are partially due to the presence of a complement-facilitated humoral immune response analogous to that described in mammalian systems.

Role of divalent metal ions in serum complement activity of the American alligator (Alligator mississippiensis)

Treatment of alligator serum with different concentrations of EDTA resulted in a concentration-dependent inhibition of serum-mediated sheep red blood cell (SRBC) hemolysis. This inhibition of serum-dependent hemolysis was observed for other chelators of divalent metal ions, such as phosphate and citrate. Treatment of alligator serum with 5 mM EDTA completely inhibited SRBC hemolysis, which could be totally restored by the addition of 5 mM Ca(2+) or Mg(2+), but not Cu(2+) or Ba(2+). These data indicate a specific need for Ca(2+) and/or Mg(2+) in the serum-mediated hemolysis of SRBCs. Kinetic analyses revealed that the addition of 30 mM EDTA 1 min after incubation of SRBCs with serum resulted in only 30% inhibition of hemolytic activity. However, addition of EDTA as early as 3 min post-incubation resulted in complete SRBC hemolysis. Pretreatment of serum with EDTA inhibited the hemolytic activity, but the activity could be restored in a time-dependent manner by the addition of Ca(2+)or Mg(2+). These data indicate that, as in human serum, the need for divalent metal ions occurs early in the alligator serum complement cascade.

Hepatitis C virus, cryoglobulinaemia, and vasculitis: immune complex relations

Several viruses are involved in the development of systemic vasculitides. Hepatitis C virus (HCV) has been shown to be closely related to mixed cryoglobulinaemia, an immune complex-mediated vasculitis. HCV particles and non-enveloped nucleocapsid protein participate in the formation of immune complexes. Once formed, immune complexes precipitate in many organs, including the skin, kidneys, and peripheral nerve fibres. Viral proteins confer peculiar physical and chemical properties on cryoimmunoglobulins. Since expansion of rheumatoid factor-synthesising B cells is the biological hallmark of mixed cryoglobulinaemia, it may be that the combination of rheumatoid factor activity and cryoprecipitability is responsible for the vasculitis. B-cell clonal expansion occurs primarily in the liver and correlates with a high intrahepatic viral load, pointing to a major role for HCV in the emergence and maintenance of B-cell clonalities. Recognition of HCV as an aetiological factor in most cryoglobulinaemic vasculitides has dramatically changed the approach to their treatment. Emphasis, in fact, is now placed on abatement of the viral load and deletion of B-cell clonalities.

Role of peritoneal mesothelial cells in peritonitis

Background

Peritoneal mesothelial cells have a remarkable capacity to respond to peritoneal insults. They generate an intense biological response and play an important role in the formation of adhesions. This review describes these activities and comments on their relationship to surgical drainage, peritoneal lavage and laparostomy in the management of patients with peritonitis.

Methods and results

Material was identified from previous review articles, references cited in original papers and a Medline search of the literature. The peritoneal mesothelium adapts to peritonitis by facilitating the clearance of contaminated fluid from the peritoneal cavity and inducing the formation of fibrinous adhesions that support the localization of contaminants. In addition, the fluid within the peritoneal cavity is a battleground in which effector mechanisms generated with the involvement of peritoneal mesothelial cells meet the contaminants. The result is a complex mix of cascading processes that have evolved to protect life in the absence of surgery.

Conclusion

Future advances in the management of patients with severe peritonitis may depend upon molecular strategies that modify the activity of peritoneal mesothelial cells.

Physiologic role of the complement system in host defense, disease, and malnutrition

The role of the complement system as a system merging early-phase innate immunity with later-phase acquired immunity has been established. C3 is a key protein of the complement system. It is activated in four pathways: (1) the alternative pathway, (2) the mannan binding protein pathway, (3) the C-reactive protein pathway, and (4) the natural IgM pathway in innate immunity. It is also activated in (1) a classic pathway, i.e., through an antigen-antibody complex, and (2) by injured host cells in acquired immunity. Activation of C3 results in a variety of immunologic reactions such as immune adherence, phagocytosis, antibody response, cytolysis, inflammation, and killing of pathogenic microorganisms. Pathologic pictures of the complement system in various diseases were reviewed. Attention was focused on hypocomplementemia in the malnourished state. In humans and in experimental animals, reduced complement levels, especially of C3, were observed in relation to lowered host defense against infection. Hypocomplementemia improved after nutritional rehabilitation with a concomitant improvement of the clinical picture and recovery of host resistance. Enhancement of C3 levels in malnourished or well-nourished rats resulted in heightened resistance against bacterial infections. On the basis of these experimental and clinical observations, we obtained clues to prevent or treat a compromised host defense system in malnourished states.

The pathobiology of peritonitis

The peritoneum is more than a mechanical covering that allows for the easy gliding of opposed peritoneal surfaces. The peritoneal mesothelial cells facilitate the action of powerful innate immune mechanisms. In addition, the peritoneal-associated lymphoid tissues contain unique cells that may play a crucial role in the localization of intraperitoneal infection. A clearer understanding of the molecular and cellular events underlying peritoneal functions in both the unstimulated and stimulated state will aid future treatment of peritonitis.

Complement receptors in HIV infection

The complement system plays an important role in the antimicrobial defense of the organism. Its components recognize a large variety of pathogens and target them for destruction, either directly by formation of a membrane attack complex or indirectly by recruiting phagocytic cells. In addition, it has several functions in cell activation, clearance of immune complexes, control of inflammatory reactions, chemotaxis and autoimmunity. For mediation of all these tasks of the complement system, complement receptor molecules on the cell surface play a key role. Current knowledge on structure, function, signal transduction and associated molecules is briefly summarized here. The role of complement receptors for human immunodeficiency virus (HIV)-associated pathogenesis is ambiguous and varies depending on cell type. On the one hand, complement receptors support the infected host to manage HIV infection and to defend itself, at least partially, against viral spreading throughout the organism. Such complement receptor-mediated supporting mechanisms are activation of immune cells and lysis of viral particles and infected host cells. On the other hand, HIV employs complement receptors to intrude more easily into various cell types, to become localized into lymph follicles and to activate viral replication in latently infected cells. This review summarizes the complex interaction of virus and complement receptors in HIV infection for different cell types.

In vitro accommodation of immortalized porcine endothelial cells: resistance to complement mediated lysis and down-regulation of VCAM expression induced by low concentrations of polyclonal human IgG antipig antibodies

The capacity of vascularized xenografts to survive in the face of normal levels of circulating antigraft antibodies and complement has been ascribed to a phenomenon referred to as "endothelial cell accommodation." The mechanisms whereby accommodation might occur have remained obscure. We have investigated this phenomenon in an in vitro system. A preparation of polyclonal immunoglobulin, human normal globulin (HNG), induced a change in the phenotype of immortalized porcine endothelial cells (IPEC) suggestive of accommodation; the cells became resistant to complement mediated lysis and displayed a reduced expression of surface VCAM and MHC class I. The accommodated phenotype only manifested after 72 hr incubation with HNG and was optimal after 120 hr. In an analysis of all the experiments performed, the development of resistance to complement mediated lysis appeared independent of the inducing dose of HNG. However, down-regulation of VCAM was only manifest when subsaturating doses were used. Our results suggest that IgG xenoreactive antibodies can mediate changes in porcine endothelial cell phenotype consistent with accommodation. The dependence on both time and dose of antibody applied might explain why accommodation has been difficult to achieve consistently in in vivo models of discordant xenotransplantation. By demonstrating a functional interaction between human VLA-4 and porcine VCAM, we speculate that the down-regulation in expression of VCAM on accommodated endothelium may have an important regulatory effect on traffic of inflammatory cells into xenografts. Our results have important implications for the development of strategies to promote accommodation of xenografts.

Peritoneal defences and peritoneum-associated lymphoid tissue

The peritoneum is mainly protected by the innate immune system. This consists of mechanical clearance of the peritoneal cavity, activation of complement, and the actions of polymorphonuclear neutrophils and macrophages. The specific immune system, which is mediated by the activity of lymphocytes, provides a secondary amplification system that may be of great importance for patients with intraperitoneal sepsis. This review provides an overview of the relevant innate immune mechanisms and explores the possible role of peritoneum-associated lymphoid tissue.