Meningococcal disease and polymorphism of FcgammaRIIa (CD32) in late complement component-deficient individuals

Functional Interactions of Common Allotypes of Rhesus Macaque FcγR2A and FcγR3A with Human and Macaque IgG Subclasses

The rhesus macaque is an important animal model for AIDS and other infectious diseases. However, the investigation of Fc-mediated Ab responses in macaques is complicated by species-specific differences in FcγRs and IgG subclasses relative to humans. To assess the effects of these differences on FcγR-IgG interactions, reporter cell lines expressing common allotypes of human and rhesus macaque FcγR2A and FcγR3A were established. FcγR-mediated responses to B cells were measured in the presence of serial dilutions of anti-CD20 Abs with Fc domains corresponding to each of the four subclasses of human and rhesus IgG and with Fc variants of IgG1 that enhance binding to FcγR2A or FcγR3A. All of the FcγRs were functional and preferentially recognized either IgG1 or IgG2. Whereas allotypes of rhesus FcγR2A were identified with responses similar to variants of human FcγR2A with higher (H131) and lower (R131) affinity for IgG, all of the rhesus FcγR3A allotypes exhibited responses most similar to the higher affinity V158 variant of human FcγR3A. Unlike responses to human IgGs, there was little variation in FcγR-mediated responses to different subclasses of rhesus IgG. Phylogenetic comparisons suggest that this reflects limited sequence variation of macaque IgGs as a result of their relatively recent diversification from a common IGHG gene since humans and macaques last shared a common ancestor. These findings reveal species-specific differences in FcγR-IgG interactions with important implications for investigating Ab effector functions in macaques.

Human genetics of meningococcal infections

Neisseria meningitidis is a leading cause of bacterial septicaemia and meningitis worldwide. Meningococcal disease is rare but can be life threatening with a tendency to affect children. Many studies have investigated the role of human genetics in predisposition to N. meningitidis infection. These have identified both rare single-gene mutations as well as more common polymorphisms associated with meningococcal disease susceptibility and severity. These findings provide clues to the pathogenesis of N. meningitidis, the basis of host susceptibility to infection and to the aetiology of severe disease. From the multiple discoveries of monogenic complement deficiencies to the associations of complement factor H and complement factor H-related three polymorphisms to meningococcal disease, the complement pathway is highlighted as being central to the genetic control of meningococcal disease. This review aims to summarise the current understanding of the host genetic basis of meningococcal disease with respect to the different stages of meningococcal infection.

Mind the Gap: How Interspecies Variability in IgG and Its Receptors May Complicate Comparisons of Human and Non-human Primate Effector Function

The field of HIV research relies heavily on non-human primates, particularly the members of the macaque genus, as models for the evaluation of candidate vaccines and monoclonal antibodies. A growing body of research suggests that successful protection of humans will not solely rely on the neutralization activity of an antibody's antigen binding fragment. Rather, immunological effector functions prompted by the interaction of the immunoglobulin G constant region and its cognate Fc receptors help contribute to favorable outcomes. Inherent differences in the sequences, expression, and activities of human and non-human primate antibody receptors and immunoglobulins have the potential to produce disparate results in the observations made in studies conducted in differing species. Having a more complete understanding of these differences, however, should permit the more fluent translation of observations between model organisms and the clinic. Here we present a guide to such translations that encompasses not only what is presently known regarding the affinity of the receptor-ligand interactions but also the influence of expression patterns and allelic variation, with a focus on insights gained from use of this model in HIV vaccines and passive antibody therapy and treatment.

Seroprevalence of Antibody-Mediated, Complement-Dependent Opsonophagocytic Activity against Neisseria meningitidis Serogroup B in England

The correlate of protection for the licensure of meningococcal vaccines is serum bactericidal activity. However, evidence indicates that a complex situation and other mechanisms, such as antibody-mediated, complement-dependent opsonophagocytosis (OP), may play a role in protection and should be investigated in order to understand immunity to this disease. In this study, a high-throughput flow cytometric opsonophagocytic assay (OPA) was optimized. The assay measures the presence of killed fluorescently labeled Neisseria meningitidis within human granulocytes (differentiated HL60 cells) by flow cytometry, using IgG-depleted pooled human plasma as an exogenous source of complement. This method was found to be reliable and correlated with the results of an opsonophagocytic killing assay. The OPA was used to measure OP activity in 1,878 serum samples from individuals ranging from 0 to 99 years of age against N. meningitidis strain NZ98/254 (B:4:P1.7-2,4). The levels of OP activity in individual serum samples varied greatly. OP activity showed an initial peak in the 6- to 12-month age group corresponding to a peak in disease incidence. The OP activity dropped in childhood until the late teenage years, although there was still a higher percentage of individuals with OP activity than with protective bactericidal antibody titers. OP activity reached a peak in the 30- to 39-year age group and then declined. This later peak in OP activity did not coincide with the young adults in whom peak serum bactericidal activity and disease incidence occurred. The demonstration of OP activity when disease incidence is low and when protective bactericidal antibody titers are not detected may indicate a role for OP in protection from meningococcal disease in these age groups.

The role of B cells and humoral immunity in Mycobacterium tuberculosis infection

Mycobacterium tuberculosis remains a major public health burden. It is generally thought that while B cell- and antibody-mediated immunity plays an important role in host defense against extracellular pathogens, the primary control of intracellular microbes derives from cellular immune mechanisms. Studies on the immune regulatory mechanisms during infection with M. tuberculosis, a facultative intracellular organism, has established the importance of cell-mediated immunity in host defense during tuberculous infection. Emerging evidence suggest a role for B cell and humoral immunity in the control of intracellular pathogens, including obligatory species, through interactions with the cell-mediated immune compartment. Recent studies have shown that B cells and antibodies can significantly impact on the development of immune responses to the tubercle bacillus. In this review, we present experimental evidence supporting the notion that the importance of humoral and cellular immunity in host defense may not be entirely determined by the niche of the pathogen. A comprehensive approach that examines both humoral and cellular immunity could lead to better understanding of the immune response to M. tuberculosis.

Meningococcal disease and the complement system

Despite considerable advances in the understanding of the pathogenesis of meningococcal disease, this infection remains a major cause of morbidity and mortality globally. The role of the complement system in innate immune defenses against invasive meningococcal disease is well established. Individuals deficient in components of the alternative and terminal complement pathways are highly predisposed to invasive, often recurrent meningococcal infections. Genome-wide analysis studies also point to a central role for complement in disease pathogenesis. Here we review the pathophysiologic events pertinent to the complement system that accompany meningococcal sepsis in humans. Meningococci use several often redundant mechanisms to evade killing by human complement. Capsular polysaccharide and lipooligosaccharide glycan composition play critical roles in complement evasion. Some of the newly described protein vaccine antigens interact with complement components and have sparked considerable research interest.

Pharmacokinetics, pharmacodynamics and physiologically-based pharmacokinetic modelling of monoclonal antibodies

Development of monoclonal antibodies (mAbs) and their functional derivatives represents a growing segment of the development pipeline in the pharmaceutical industry. More than 25 mAbs and derivatives have been approved for a variety of therapeutic applications. In addition, around 500 mAbs and derivatives are currently in different stages of development. mAbs are considered to be large molecule therapeutics (in general, they are 2-3 orders of magnitude larger than small chemical molecule therapeutics), but they are not just big chemicals. These compounds demonstrate much more complex pharmacokinetic and pharmacodynamic behaviour than small molecules. Because of their large size and relatively poor membrane permeability and instability in the conditions of the gastrointestinal tract, parenteral administration is the most usual route of administration. The rate and extent of mAb distribution is very slow and depends on extravasation in tissue, distribution within the particular tissue, and degradation. Elimination primarily happens via catabolism to peptides and amino acids. Although not definitive, work has been published to define the human tissues mainly involved in the elimination of mAbs, and it seems that many cells throughout the body are involved. mAbs can be targeted against many soluble or membrane-bound targets, thus these compounds may act by a variety of mechanisms to achieve their pharmacological effect. mAbs targeting soluble antigen generally exhibit linear elimination, whereas those targeting membrane-bound antigen often exhibit non-linear elimination, mainly due to target-mediated drug disposition (TMDD). The high-affinity interaction of mAbs and their derivatives with the pharmacological target can often result in non-linear pharmacokinetics. Because of species differences (particularly due to differences in target affinity and abundance) in the pharmacokinetics and pharmacodynamics of mAbs, pharmacokinetic/pharmacodynamic modelling of mAbs has been used routinely to expedite the development of mAbs and their derivatives and has been utilized to help in the selection of appropriate dose regimens. Although modelling approaches have helped to explain variability in both pharmacokinetic and pharmacodynamic properties of these drugs, there is a clear need for more complex models to improve understanding of pharmacokinetic processes and pharmacodynamic interactions of mAbs with the immune system. There are different approaches applied to physiologically based pharmacokinetic (PBPK) modelling of mAbs and important differences between the models developed. Some key additional features that need to be accounted for in PBPK models of mAbs are neonatal Fc receptor (FcRn; an important salvage mechanism for antibodies) binding, TMDD and lymph flow. Several models have been described incorporating some or all of these features and the use of PBPK models are expected to expand over the next few years.

Genetics and genomics in pediatric septic shock

OBJECTIVES

Pediatric septic shock continues to be an important public health problem. Several investigative groups have applied genetic and genomic approaches as a means of identifying novel pathways and therapeutic targets, discovery of sepsis-related biomarkers, and identification of septic shock subclasses. This review will highlight studies in pediatric sepsis with a focus on gene association studies and genome-wide expression profiling.

DATA SOURCES

A summary of published literature involving gene association and expression profiling studies specifically involving pediatric sepsis and septic shock.

SUMMARY

Several polymorphisms of genes broadly involved in inflammation, immunity, and coagulation have been linked with susceptibility to sepsis, or outcome of sepsis in children. Many of these studies involve meningococcemia, and the strongest association involves a functional polymorphism of the plasminogen activator inhibitor-1 promoter region and meningococcal sepsis. Expression profiling studies in pediatric septic shock have identified zinc supplementation and inhibition of matrix metalloproteinase-8 activity as potential, novel therapeutic approaches in sepsis. Studies focused on discovery of sepsis-related biomarkers have identified interleukin-8 as a robust outcome biomarker in pediatric septic shock. Additional studies have demonstrated the feasibility and clinical relevance of gene expression-based subclassification of pediatric septic shock.

CONCLUSIONS

Pediatric sepsis and septic shock are increasingly being studied by genetic and genomic approaches and the accumulating data hold the promise of enhancing our future approach to this ongoing clinical problem.

Mechanisms and regulation of the gene-expression response to sepsis

Sepsis is defined as the systemic inflammatory response of the human host that is triggered by an invading pathogen. Despite tremendous advances in both our knowledge of and treatment strategies for this syndrome, sepsis remains among the major causes of morbidity and mortality in children worldwide. Thus, we hypothesize that an improved mechanistic understanding obtained via basic and translational science will continue to identify novel therapeutic targets and approaches. As a result, given the central importance of the alterations in gene expression in regulating the human host's physiologic response to a pathogen, we review the complex factors-genetics, transcriptional expression, and epigenetics-that regulate unique gene-expression patterns in pediatric sepsis and septic shock. We anticipate that emerging data from genetic, genomic, and other translation studies in pediatric sepsis will advance our biological understanding of this response and undoubtedly identify targets for newer therapies.

Functional and clinical consequences of Fc receptor polymorphic and copy number variants

Receptors for immunoglobulins (Fc receptors) play a central role during an immune response, as they mediate the specific recognition of antigens of almost infinite diversity by leucocytes, thereby linking the humoral and cellular components of immunity. Indeed, engagement of Fc receptors by immunoglobulins initiates a range of immunoregulatory processes that might also play a role in disease pathogenesis. In the circulation, five main types of immunoglobulins (Ig) exist - namely IgG, IgA, IgE, IgM and IgD and receptors with the ability to recognize and bind to IgG (Fc gamma receptor family), IgE (Fc epsilon RI and CD23), IgA (CD89; Fc alpha/microR) and IgM (Fc alpha/microR) have been identified and characterized. However, it is astonishing that nearly all the known human Fc receptors display extensive genetic variation with clear implications for their function, thus representing a substantial genetic risk factor for the pathogenesis of a range of chronic inflammatory disorders.

Infectious complications after chemotherapy and stem cell transplantation in multiple myeloma: implications of Fc gamma receptor and myeloperoxidase promoter polymorphisms

Multiple myeloma is associated with a high risk of infections. We hypothesized that Fc gamma receptor (FCGR) and myeloperoxidase (MPO) promoter gene polymorphisms influence the risk of infections after induction chemotherapy (IC) and autologous stem cell transplantation (ASCT). Retrospectively, we analysed 136 patient courses of IC and 113 procedures of ASCT. Genetic analyses were made with PCR techniques on genomic DNA. The incidence rate ratio of sepsis during ASCT in patients homozygous for the G-129MPO promoter type was 0.30 (95% CI: 0.09-0.96). The G-463AMPO promoter polymorphism was not associated with the risk of infections. The polymorphisms of FCGR2A, FCGR3A and FCGR3B were not convincingly associated with infections. The NA1 variant of FCGR3B was strongly skewed with other risk factors, and the results in IC and ASCT were conflicting. Further studies of the G-129AMPO promoter as a potential risk modifier for infections are relevant.

Prognostic value of phagocytic activity of neutrophils and monocytes in sepsis. Correlation to CD64 and CD14 antigen expression

The role of the phagocytic function of monocytes and neutrophils in sepsis has been poorly investigated. The present study evaluated the impact of the phagocytic activity of neutrophils and monocytes on the outcome of patients with severe sepsis. Thirty-one patients and 30 healthy individuals were enrolled in the study. The phagocytic activity of monocytes and neutrophils was evaluated during 24 h after admission and the results were correlated to the expression of CD64 on neutrophils and monocytes, CD14 antigen on monocytes, the Simplified Acute Physiology Score II and the patients' survival. A reduced phagocytic activity of neutrophils during the first 24 h after admission was a negative predictor for survival. Increased expression of CD64 antigen on polymorphonuclear cells (PMNs) and monocytes was favourably correlated to the patients' survival. In multivariate analysis the phagocytic activity of PMNs was the only independent predictor factor for survival. Patients with PMN phagocytic activity <37% had lower expression of CD64 on monocytes and PMNs and worse outcome, while those with phagocytic activity >37% had higher expression of CD64 on monocytes and PMNs and better outcome. Reduced phagocytic activity of neutrophils may represent a state of neutrophil inactivation similar to that previously described for monocytes during the compensatory anti-inflammatory response.

Genetic approach to pediatric septic shock

Septic shock is a complex and heterogeneous clinical syndrome, triggered by infection, and having significant morbidity and mortality in children. Emerging data indicate that the genetic make-up of the pediatric host may have a strong influence on the development and outcome of septic shock in children. Herein, we review this broad topic by focusing on pediatric-specific data (both recent and historical), as well as the broad topics of SNPs, genome-wide association studies and epigenetics. The historical and emerging data strongly suggest that a genetics-based perspective will need to be considered in future investigations and strategies aimed at improving the outcome of children with septic shock.

Induction of Fc gammaRIIA expression in myeloid PLB cells during differentiation depends on cytosolic phospholipase A2 activity and is regulated via activation of CREB by PGE2

Fc gammaRIIA expressed on neutrophils and monocytes has a fundamental role in combating bacterial infections. In the present study, the requirement of cytosolic phospholipase A2 (cPLA2) for induction of Fc gammaRIIA expression was studied in a model of cPLA2-deficient PLB-985 cells (PLB-D cells). Fc gammaRIIA was acquired only during differentiation of PLB but not of PLB-D cells induced by either 1,25-dihydroxyvitamin D3, retinoic acid, or interferon gamma. Addition of prostaglandin E2 (PGE2) to PLB-D cells undergoing differentiation restored the expression of Fc gammaRIIA protein, whereas addition of indomethacin to PLB cells during differentiation inhibited both the production of PGE2 and the expression of Fc gammaRIIA. Inhibition of PKA during PLB differentiation prevented Fc gammaRIIA expression, whereas dibutyryl cAMP (dbcAMP) induced its expression in both PLB and PLB-D cells. CREB phosphorylation and CREB-CRE interaction were detected only in differentiated PLB cells and not PLB-D cells and were inhibited by indomethacin. A reporter gene containing a Fc gammaRIIA gene promoter fragment with the CRE element was sufficient for CREB activation. Our results are the first to show that CREB activation is involved in up-regulation of Fc gammaRIIA expression in myeloid lineages. PGE2 formed via cPLA2 activates CREB through PKA and this process is dependent on development of PGE2 receptor 4.

Complement deficiency and disease: an update

Complement deficiencies are probably vastly under-diagnosed within clinical medicine. Judging from a Swedish study of C2 deficiency, a deficiency with an estimated prevalence of about 1/20,000 in Western countries, less than 10% of the deficiencies of the classical and alternative pathways and the late complement components are identified in Sweden. C1 inhibitor deficiency and deficiencies of MBL and MASP-2 were not included in the assessment. The introduction of new screening methods should facilitate detection of complement deficiencies in clinical practice. In our study of C2 deficiency (n=40), 57% of the patients had a history of invasive infection with encapsulated bacteria, mainly Streptococcus pneumoniae. This emphasizes the importance of the classical and/or the lectin pathway in defence against severe infection. Rheumatological disease, mainly systemic lupus erythematosus was present in 43% of the patients. In addition, a significant association was found between C2 deficiency and atherosclerosis. Complement-dependent disease mechanisms are discussed together with the potential importance of non-complement genes for disease expression in complement deficiencies. Analysis of larger patient groups is required in order to establish guidelines for investigation and treatment of patients with complement deficiency.

Fc RIIIb and Complement Component C7 Codeficiency in a Patient with Recurrence of Fulminant Meningococcal Septic Shock

Individuals with deficiencies of the late components of complement exhibit a susceptibility to the recurrence of meningococcal disease with a usually mild clinical presentation. We report the recurrence of fulminant meningococcal disease in a complement component C7-deficient patient. We found a total deficiency of FcgammaRIIIb on neutrophils, which could partially explain the unusually severe clinical presentation.

Genetic polymorphisms in sepsis

CONTEXT

Wide variability exists in the susceptibility to and outcome from sepsis even within similar intensive care unit populations. Some of this variability in the host may be due to genetic variation in genes coding for components of the innate immune response.

OBJECTIVE

To review the evidence for a genetic influence on the susceptibility to and outcome from sepsis.

DESIGN

Literature review.

PATIENTS

Variety of adult and pediatric patients with various critical illnesses and infections.

INTERVENTIONS

None.

MAIN OUTCOME MEASURES

Susceptibility to clinical symptoms of sepsis and outcome as measured by severity of disease and mortality.

RESULTS

Polymorphisms in genes coding for proteins involved in the recognition of bacterial pathogens (Toll-like receptor 4, CD14, Fc(gamma)RIIa, and mannose-binding lectin) and the response to bacterial pathogens (tumor necrosis factor-alpha, interleukin (IL)-1alpha, IL-1beta, IL-1 receptor agonist, IL-6, IL-10, heat shock proteins, angiotensin I converting enzyme, plasminogen activator inhibitor-1) can influence the amount or function of the protein produced in response to bacterial stimuli. Evidence is discussed suggesting that some of these genetic polymorphisms influence the susceptibility to and outcome from sepsis.

CONCLUSION

Host genetic variability in the regulatory and coding regions of genes for components of the innate immune system may influence the susceptibility to and/or outcome from sepsis. The disparate results observed in many studies of polymorphisms in sepsis emphasize the need for future studies to be larger, to include the analysis of multiple polymorphisms, and to be better designed with respect to control populations to identify the degree of influence that genetic variability has on sepsis.

Hereditary C2 deficiency in Sweden: frequent occurrence of invasive infection, atherosclerosis, and rheumatic disease

Although frequently asymptomatic, homozygous C2 deficiency (C2D) is known to be associated with severe infections and rheumatic disease. We describe the clinical findings in 40 persons with C2D from 33 families identified in Sweden over 25 years. Medical records covering 96% of the accumulated person-years were reviewed, giving a mean observation time of 39 years (range, 1-77 yr). Severe infection was the predominant clinical manifestation in the cohort: 23 patients had a past history of invasive infections, mainly septicemia or meningitis caused by Streptococcus pneumoniae, and 12 patients had repeated infections of this kind. Nineteen patients had at least 1 episode of pneumonia, and recurrent pneumonia was documented in 10 patients. Repeated infections occurred mainly during infancy and childhood. Systemic lupus erythematosus was found in 10 patients. Another 7 patients had undifferentiated connective tissue disease (n = 4) or vasculitis (n = 3). We found no correlation between susceptibility to invasive infection and rheumatologic disease. Cardiovascular disease occurred at a high rate, with a total of 10 acute myocardial infarctions and 5 cerebrovascular episodes in 6 patients. Causes of death among the C2D patients were infection (n = 5), acute myocardial infarction (n = 3), and cancer (n = 1). We suggest that severe infection may be the principal clinical manifestation of C2D. We also provide novel evidence for a possible role of C2D in the development of atherosclerosis consistent with findings in mannan-binding deficiency and experimental C3 deficiency. In addition, we confirm the well-known association between C2D and systemic lupus erythematosus.

Analysis of Fc gamma receptor II (CD32) polymorphism in populations of African and South Asian ancestry reveals east-west geographic gradients of allele frequencies

Analysis of FcgammaRIIA alleles in Pakistanis and in Trinidadians of South Asian, African and mixed ancestry revealed no significant differences between Trinidadian South Asians and Pakistanis. H131 homozygotes were more common among Trinidadian South Asians than among Africans and those of mixed ancestry. Comparison with other populations revealed east-west geographic gradients of allele frequencies.

Host genetic determinants of Neisseria meningitidis infections

The clinical presentation of infections caused by Neisseria meningitidis is highly diverse. Some patients develop meningitis, and others present with sepsis or even septic shock. After invasion of the bloodstream by the bacteria, three main cascade pathways are activated. These are the complement system, the inflammatory response, and the coagulation and fibrinolysis pathway. These pathways do not act independently but are able to interact with each other. Genetic polymorphisms among components of these pathways have been shown to be involved in the susceptibility, severity, and outcome of meningococcal disease. We review knowledge of genetic variations associated with susceptibility to and severity of meningococcal infection. Complement deficiencies and defects in sensing or opsonophagocytic pathways, such as the rare Toll-like receptor 4 single nucleotide polymorphisms (SNPs) and combinations of inefficient variants of Fcgamma-receptors, seem to have the most important role in genetically established susceptibility. Effect on severity has repeatedly been reported for FcgammaRIIa and plasminogen activator inhibitor type 1 (PAI1) polymorphisms. Outcome effects have been confirmed for SNPs in properdin deficiencies, PAI1 and combination of the -511C/T SNP in interleukin 1beta, and the +2018C/T SNP in interleukin RN. Conflicting results are reported for the effect of the -308G/A promoter polymorphism in tumour necrosis factor (TNF) alpha. These differences may reflect discrepancies in group definitions between studies or the influence of additional SNPs in the TNFalpha promoter, which can form haplotypes representing different cytokine production capacity. For several SNPs, the potential effect on susceptibility, severity, or outcome has not yet been confirmed in an independent study.

Complement component C7 deficiency in a Spanish family

Different genetic mutations have been described in complement component C7 deficiency, a molecular defect which is clinically associated with an increased susceptibility to neisserial recurrent infections, although some cases remain asymptomatic. In this work we report the genetic bases of C7 deficiency in one Spanish family. Exon-specific PCR and sequencing revealed a novel point mutation at nucleotide 615 (exon 6) leading to a stop codon (UGG to UGA) in the patient, his mother, and sister. This transversion causes the premature truncation of the C7 protein (W183X). Additionally, we detected a missense mutation at position 1135 (exon 9) located in the first nucleotide of the codon GGG (CGG), resulting in an amino acid change (G357R) in the patient, his father, as well as in his sister. This latter mutation had been previously described in individuals from Moroccan Sephardic Jewish ancestry. Since both heterozygous mutations were found in the patient as well as in his asymptomatic sister, we analyse other meningococcal defence mechanisms such as polymorphisms of the opsonin receptors on polymorphonuclear cells. Results showed that the patient and his sister bore identical combinations of FcgammaRIIA-H/R131 and FcgammaRIIIB-NA1/2 allotypes. Our results provide further evidence that the molecular pathogenesis of C7 deficiency as well as susceptibility to meningococcal disease are heterogeneous, since different families carry different molecular defects, although many of the C7 defects appear to be homogeneous in individuals from certain geographical areas. The missense mutation G357R would make an interesting topic of analysis with regard to meningococcal disease susceptibility in the Spanish population.

Redox regulation of Fcgamma receptor-mediated phagocytosis: implications for host defense and tissue injury

Recent advances in our understanding of the mechanisms that regulate acute and chronic inflammatory responses have revealed a key role for reactive oxygen intermediates in modulating the activation of neutrophils. Opsonized microbes and immune complexes initiate the oxidative burst by the engagement of receptors for immunoglobulin G, termed Fcgamma receptors. The regulation of phagocytic cell function by oxidant-sensitive signaling pathways optimizes host defense capabilities, but it also amplifies tissue damage. This review will focus on the cross-talk between Fcgamma receptors and reactive oxygen intermediates at sites of inflammation and its role in microbial immunity.

Bench-to-bedside review: genetic influences on meningococcal disease

This review discusses the possible involvement of a variety of genetic polymorphisms on the course of meningococcal disease. It has been shown that several common genetic polymorphisms can either influence the susceptibility to meningococcal disease or can account for a higher mortality rate in patients. Gene polymorphisms concerning antibody receptors, lipopolysaccharide (LPS) binding receptors or proteins, innate complement proteins as well as cytokines and hemostatic proteins are described. The study of genetic polymorphisms might provide important insights in the pathogenesis of meningococcal disease and could make it possible to identify individuals who are at risk of either contracting or dying from meningococcal disease.

Associations between Fc gamma receptor IIA polymorphisms and the risk and prognosis of meningococcal disease

BACKGROUND

In vitro studies have shown that the neutrophil Fc gamma receptor IIA (FcgammaRIIA) polymorphism influences the phagocytic capacity of neutrophils and the removal of encapsulated bacteria from the bloodstream. In particular, the R/R131 allotype is associated with less phagocytic activity.

SUBJECTS AND METHODS

We performed a case-control study to determine the influence of the FcgammaRIIA polymorphism (R/R131, R/H131, H/H131) on the risk and outcome of meningococcal disease. The polymorphisms were measured in 130 patients with microbiologically proven meningococcal disease diagnosed from 1987 to 1998 (cases) and 260 asymptomatic sex-matched blood donors (controls). Clinical manifestations and complications of meningococcal disease were recorded, and a prognostic score (based on age, hemorrhagic diathesis, neurologic signs, and the absence of preadmission antibiotic) therapy was calculated.

RESULTS

The distributions of FcgammaRIIA allotypes were similar in cases and controls. However, among patients with meningococcal infection, fulminant meningococcal disease (odds ratio [OR] = 3.9; 95% confidence interval [CI]: 1.0 to 16; P = 0.04) and meningococcemia without meningitis (OR = 3.0; 95% CI: 1.4 to 7.8; P = 0.004) were more common in those with the FcgammaRIIA-R/R131 allotype. Complications were also significantly more frequent in these patients. Of the 42 patients with the R/R131 allotype, 31 (74%) had an adverse prognostic score, compared with 7% (4 of 59) of those with the R/H131 allotype and 3% (1 of 29) of those with the H/H131 allotype (P <0.0001).

CONCLUSION

The FcgammaRIIA-R/R131 allotype is associated with more severe forms of meningococcal disease.

Fcgamma receptor polymorphisms in populations in Ethiopia and Norway

Seventy-seven healthy Ethiopians were genotyped for polymorphisms in the immunoglobulin G Fc receptors (FcgammaR) FcgammaRIIa, FcgammaRIIIa and FcgammaRIIIb, including the SH allele. The genotype and allele frequencies were compared with those of 96 healthy Norwegians. Ethiopians had higher frequencies of the SH-FcgammaRIIIb (P = 0.001), FcgammaRIIIa-158 V (P = 0.026) and FcgammaRIIIb-Na2 (P = 0.046) alleles. The genotype distributions of FcgammaRIIa, FcgammaRIIIa and FcgammaRIIIb, however, did not differ significantly from those of the Norwegians. The data were also compared with those reported from studies on other ethnic groups. The variation of different polymorphisms both within and between ethnic groups may influence differences in the incidence rates of infectious and autoimmune diseases.

Human receptors for immunoglobulin G: key elements in the pathogenesis of rheumatic disease

The structural diversity of Fc gammaR provides a mechanism by which IgG can elicit a broad range of cell responses. Fc gammaR vary in their affinity for IgG, their preference for IgG subclasses, the cell types in which they are expressed, and the intracellular signals which they elicit--stimulatory or inhibitory. Expansion in our knowledge of structure-function relationships among Fc gammaR has identified them as heritable risk factors for disease susceptibility and valuable targets for therapeutic modulation of the immune system.

New insights into endotoxin-induced activation of macrophages: involvement of a K+ channel in transmembrane signaling

LPS (endotoxins) activate cells of the human immune system, among which are monocytes and macrophages, to produce endogenous mediators. These regulate the immune response, but may also cause severe harm leading to septic shock. The activation of monocytes/macrophages by LPS is mediated by a membrane-bound LPS receptor, mCD14. As mCD14 lacks a transmembrane domain, a further protein is required for the signal transducing step to the cell interior. Here we show, using excised outside-out membrane patches, that activation of a high-conductance Ca(2+)- and voltage-dependent potassium channel is an early step in the transmembrane signal transduction in macrophages. The channel is activated by endotoxically active LPS in a dose-dependent manner. Channel activation can be completely inhibited by LPS antagonists and by anti-CD14 Abs. Activation of the channel is essential for LPS-induced cytokine production as shown by its inhibition by selective K(+) channel blockers.

The role of Fcgamma receptor polymorphisms and C3 in the immune defence against Neisseria meningitidis in complement-deficient individuals

Individuals with either a late (C5-9) complement component deficiency (LCCD) or properdin deficiency are at increased risk to develop meningococcal disease, often due to serogroups W135 and Y. Anti-meningococcal defence in both LCCD persons and properdin-deficient individuals without bactericidal antibodies depends mainly on phagocytosis. Three types of opsonin receptors are involved in phagocytosis by polymorphonuclear cells (PMN). These represent the polymorphic FcgammaRIIa (CD32) and FcgammaRIIIb (CD16b) receptors, and the C3 receptor CR3 (CD11b/CD18). When the distribution of FcgammaRIIa and FcgammaRIIIb allotypes was assessed in 15 LCCD and in 15 properdin-deficient patients with/without previous meningococcal disease, we found the combination of FcgammaRIIa-R/R131 with FcgammaRIIIb-NA2/NA2 allotypes to be associated with previous meningococcal disease (odds ratio 13.9, Fisher's test P = 0.036). No such relation was observed in the properdin-deficient patients. The importance of FcgammaRIIa allotypes was also demonstrated using in vitro phagocytosis assays. PMN from FcgammaRIIa-R/R131 homozygous donors internalized IgG2 opsonized meningococci W135 significantly (P < 0.05) less than PMN from FcgammaRIIa-H/H131 donors. When properdin-deficient serum was tested, it was observed that reconstitution with properdin resulted in enhanced PMN phagocytosis of the W135 meningococci (P = 0.001). This enhanced phagocytosis was parallelled by an increase in C3 deposition onto the opsonized meningococci W135 (r = 0.6568, P = 0. 01). We conclude that the occurrence of meningococcal disease in LCCD patients is associated with certain FcgammaR allotypes. Properdin-deficient individuals are susceptible to meningococcal disease because of an insufficient C3 deposition on the surface of meningococci, resulting in insufficient phagocytosis.

Protection from lethal gram-positive infection by macrophage scavenger receptor-dependent phagocytosis

Infections with gram-positive bacteria are a major cause of morbidity and mortality in humans. Opsonin-dependent phagocytosis plays a major role in protection against and recovery from gram-positive infections. Inborn and acquired defects in opsonin generation and/or recognition by phagocytes are associated with an increased susceptibility to bacterial infections. In contrast, the physiological significance of opsonin-independent phagocytosis is unknown. Type I and II class A scavenger receptors (SR-AI/II) recognize a variety of polyanions including bacterial cell wall products such as lipopolysaccharide (LPS) and lipoteichoic acid (LTA), suggesting a role for SR-AI/II in innate immunity to bacterial infections. Here, we show that SR-AI/II-deficient mice (MSR-A(-/-)) are more susceptible to intraperitoneal infection with a prototypic gram-positive pathogen, Staphylococcus aureus, than MSR-A(+/+) control mice. MSR-A(-/-) mice display an impaired ability to clear bacteria from the site of infection despite normal killing of S. aureus by neutrophils and die as a result of disseminated infection. Opsonin-independent phagocytosis of gram-positive bacteria by MSR-A(-/-) macrophages is significantly decreased although their phagocytic machinery is intact. Peritoneal macrophages from control mice phagocytose a variety of gram-positive bacteria in an SR-AI/II-dependent manner. Our findings demonstrate that SR-AI/II mediate opsonin-independent phagocytosis of gram-positive bacteria, and provide the first evidence that opsonin-independent phagocytosis plays a critical role in host defense against bacterial infections in vivo.

Variant Genotypes of the Low-Affinity Fcγ Receptors in Two Control Populations and a Review of Low-Affinity Fcγ Receptor Polymorphisms in Control and Disease Populations

Fcγ-receptors (FcγR) provide a critical link between humoral and cellular immunity. The genes of the low-affinity receptors for IgG and their isoforms, namely, FcγRIIa, FcγRIIb, FcγRIIIa, FcγRIIIb, and SH-FcγRIIIb, are located in close proximity on chromosome 1q22. Variant alleles may differ in biologic activity and a number of studies have reported the frequencies of variant FcγR alleles in both disease and control populations. No large study has evaluated the possibility of a nonrandom distribution of variant genotypes. We analyzed 395 normal individuals (172 African Americans [AA] and 223 Caucasians [CA]) at the following loci: FcγRIIa, FcγRIIIa, and FcγRIIIb, including the SH-FcγRIIIb. The genotypic distributions of FcγRIIa, FcγRIIIa, and FcγRIIIb conform to the Hardy-Weinberg law in each group. There was no strong evidence that combinations of 2-locus genotypes of the 3 loci deviated from random distributions in these healthy control populations. The distribution of SH-FcγRIIIb is underrepresented in CA compared with AA (P &lt; .0001) controls. A previously reported variant FcγRIIb was not detected in 70 normal individuals, indicating that this allele, if it exists, is very rare (&lt;1%). In conclusion, we present data that should serve as the foundation for the interpretation of association studies involving multiple variant alleles of the low-affinity FcγR.

Variant Genotypes of the Low-Affinity Fcγ Receptors in Two Control Populations and a Review of Low-Affinity Fcγ Receptor Polymorphisms in Control and Disease Populations

Fcγ-receptors (FcγR) provide a critical link between humoral and cellular immunity. The genes of the low-affinity receptors for IgG and their isoforms, namely, FcγRIIa, FcγRIIb, FcγRIIIa, FcγRIIIb, and SH-FcγRIIIb, are located in close proximity on chromosome 1q22. Variant alleles may differ in biologic activity and a number of studies have reported the frequencies of variant FcγR alleles in both disease and control populations. No large study has evaluated the possibility of a nonrandom distribution of variant genotypes. We analyzed 395 normal individuals (172 African Americans [AA] and 223 Caucasians [CA]) at the following loci: FcγRIIa, FcγRIIIa, and FcγRIIIb, including the SH-FcγRIIIb. The genotypic distributions of FcγRIIa, FcγRIIIa, and FcγRIIIb conform to the Hardy-Weinberg law in each group. There was no strong evidence that combinations of 2-locus genotypes of the 3 loci deviated from random distributions in these healthy control populations. The distribution of SH-FcγRIIIb is underrepresented in CA compared with AA (P < .0001) controls. A previously reported variant FcγRIIb was not detected in 70 normal individuals, indicating that this allele, if it exists, is very rare (<1%). In conclusion, we present data that should serve as the foundation for the interpretation of association studies involving multiple variant alleles of the low-affinity FcγR.

Properdin deficiency in a large Swiss family: identification of a stop codon in the properdin gene, and association of meningococcal disease with lack of the IgG2 allotype marker G2m(n)

Properdin deficiency was demonstrated in three generations of a large Swiss family. The concentration of circulating properdin in affected males was < 0.1 mg/l, indicating properdin deficiency type I. Two of the nine properdin-deficient males in the family had survived meningitis caused by Neisseria meningitidis serogroup B without sequel. Two point mutations were identified when the properdin gene in one of the properdin-deficient individuals was investigated by direct solid-phase sequencing of overlapping polymerase chain reaction (PCR) products. The critical mutation was found at base 2061 in exon 4, where the change of cytosine to thymine had generated the stop codon TGA. The other mutation was positioned at base 827 in intron 3. The stop codon in exon 4 was also demonstrated by standard dideoxy sequencing in three additional family members. The question was asked if genetic factors such as partial C4 deficiency and IgG allotypes could have influenced susceptibility to meningococcal disease in the family. No relationship was found between C4 phenotypes and infection. Interestingly, the two properdin-deficient males with meningitis differed from the other properdin-deficient persons in that they lacked the G2m(n) allotype, a marker known to be associated with poor antibody responses to T-independent antigens. This implies that the consequences of properdin deficiency might partly be determined by independent factors influencing the immune response.

Immunoglobulin G Fc-receptor (FcgammaR) IIA and IIIB polymorphisms related to disability in MS

OBJECTIVE

MS is immunologically mediated in genetically susceptible individuals. Receptors for the Fc fragment of immunoglobulin G (IgG) (FcgammaR) link the humoral and cellular immune responses by targeting immune complexes to effector cells. Different FcgammaR show variability in their distribution, strength, and capacity of binding different IgG subclasses.

METHODS

To investigate the role of FcgammaR in MS, 136 MS patients and 96 matched controls were genotyped for FcgammaRIIA and FcgammaRIIIB gene polymorphisms; the results were correlated to disease susceptibility and severity measured by the Expanded Disability Status Scale (EDSS).

RESULTS

The allele frequencies of the FcgammaRIIA and FcgammaRIIIB did not differ significantly between the MS patients and the controls. Patients homozygous for the FcgammaRIIIB neutrophil antigen (NA) 1 allele had a significantly more benign course of MS than patients heterozygous or homozygous for the FcgammaRIIIB NA2 allele. Patients homozygous for the FcgammaRIIA histidine (H) allele also had a more benign course of MS than patients heterozygous or homozygous for the FcgammaRIIA arginine (R) allele.

CONCLUSION

The results implicate FcgammaRIIIB and to a lesser extent FcgammaRIIA as disease-modifying genes in MS. FcgammaRIIIB NA1/NA1 and FcgammaRIIA H/H bind more efficient IgG1/IgG3 and IgG2 subclasses, respectively, than FcgammaRIIIB NA2/NA2 and FcgammaRIIA R/R. A more effective processing of circulating immune complexes may be one mechanism for better clinical outcome in MS.