Complement proteins C1q and MBL are pattern recognition molecules that signal immediate and long-term protective immune functions

Fundamental role of C1q in autoimmunity and inflammation

C1q, historically viewed as the initiating component of the classical complement pathway, also exhibits a variety of complement-independent activities in both innate and acquired immunity. Recent studies focusing on C1q's suppressive role in the immune system have provided new insight into how abnormal C1q expression and bioactivity may contribute to autoimmunity. In particular, molecular networks involving C1q interactions with cell surface receptors and other ligands are emerging as mechanisms involved in C1q's modulation of immunity. Here, we discuss the role of C1q in controlling immune cell function, including recently elucidated mechanisms of action, and suggest how these processes are critical for maintaining tissue homeostasis under steady-state conditions and in preventing autoimmunity.

Three novel C1q domain containing proteins from the disk abalone Haliotis discus discus: Genomic organization and analysis of the transcriptional changes in response to bacterial pathogens

The globular C1q (gC1q) domain containing proteins, commonly referred as C1q domain containing (C1qDC) proteins, are an essential family of proteins involved in various innate immune responses. In this study, three novel C1qDC proteins were identified from the disk abalone (Haliotis discus discus) transcriptome database and designated as AbC1qDC1, AbC1qDC2, and AbC1qDC3. The cDNA sequences of AbC1qDC1, AbC1qDC2, and AbC1qDC3 consisted of 807, 1305, and 660 bp open reading frames (ORFs) encoding 269, 435, and 220 amino acids (aa), respectively. Putative signal peptides and the N-terminal gC1q domain were identified in all three AbC1qDC proteins. An additional predicted motif region, known as the coiled coil region (CCR), was identified next to the signal sequence of AbC1qDC2. The genomic organization of the AbC1qDCs was determined using a bacterial artificial chromosome (BAC) library. It was found that the CDS of AbC1qDC1 was distributed among three exons, while the CDSs of AbC1qDC2 and AbC1qDC3 were distributed between two exons. Sequence analysis indicated that the AbC1qDC proteins shared <40% identity with other counterparts from different species. According to the neighbor-joining phylogenetic tree, the proteins were grouped within an invertebrate group with high evolutionary distances, which suggests that they are new members of the C1qDC family. Higher expression of AbC1qDC1 and AbC1qDC2 was detected in hepatopancreas, muscle, and mantle tissues compare to the other tissues analyzed, using reverse transcription, followed by quantitative real-time PCR (qPCR) using SYBR Green, whereas AbC1qDC3 was predominantly expressed in gill tissues, followed by muscles and the hepatopancreas. The temporal expression of AbC1qDC transcripts in gills after bacterial (Vibrio parahaemolyticus and Listeria monocytogenes) and lipopolysaccharide stimulation indicated that AbC1qDCs can be strongly induced by both Gram-negative and Gram-positive bacterial species with different response profiles. The results of this study suggest that AbC1qDCs are involved in immune responses against invading bacterial pathogens.

Uncoupling complement C1s activation from C1q binding in apoptotic cell phagocytosis and immunosuppressive capacity

Complement activation contributes to inflammation in many diseases, yet it also supports physiologic apoptotic cells (AC) clearance and its downstream immunosuppressive effects. The roles of individual complement components in AC phagocytosis have been difficult to dissect with artificially depleted sera. Using human in vitro systems and the novel antibody complement C1s inhibitor TNT003, we uncoupled the role of the enzymatic activation of the classical pathway from the opsonizing role of C1q in mediating a) the phagocytosis of early and late AC, and b) the immunosuppressive capacity of early AC. We found that C1s inhibition had a small impact on the physiologic clearance of early AC, leaving their immunosuppressive properties entirely unaffected, while mainly inhibiting the phagocytosis of late apoptotic/secondary necrotic cells. Our data suggest that C1s inhibition may represent a valuable therapeutic strategy to control classical pathway activation without causing significant AC accumulation in diseases without defects in AC phagocytosis.

L-C1qDC-1, a novel C1q domain-containing protein from Lethenteron camtschaticum that is involved in the immune response

The C1q domain-containing (C1qDC) proteins are a family of proteins characterized by a globular C1q (gC1q) domain at their C-terminus. These proteins are involved in various processes in vertebrates and are assumed to serve as important pattern recognition receptors in innate immunity in invertebrates. Here, a novel C1qDC protein from Lethenteron camtschaticum was identified and characterized (designated as L-C1qDC-1). After a partial cDNA sequence of L-C1qDC-1 was identified in a L. camtschaticum liver cDNA library, the full-length cDNA was obtained using 3'- and 5'-rapid amplification of cDNA ends (RACE). L-C1qDC-1 encodes 236 amino acids and contains a signal peptide, a collagen-like sequence with Gly-Xaa-Yaa repeats, and a C-terminal gC1q domain. The L-C1qDC-1 protein was primarily distributed in the gut, liver and supraneural body of L. camtschaticum and was also marginally detectable in leukocytes via real-time PCR and immunofluorescence assays. Furthermore, both immunoprecipitation and immunofluorescence results showed that in L. camtschaticum serum, L-C1qDC-1 could interact with variable lymphocyte receptor (VLR) B and displayed strong colocalization with cancer cell immune responses. These results indicated that the L-C1qDC-1 gene encodes a novel C1qDC protein that may play an important role in the immune responses of L. camtschaticum, providing clues for understanding the universal functions of C1qDC proteins in other species and suggesting that these proteins could serve as pattern recognition molecules in immunotherapy.

Complement activation in the context of stem cells and tissue repair

The complement pathway is best known for its role in immune surveillance and inflammation. However, its ability of opsonizing and removing not only pathogens, but also necrotic and apoptotic cells, is a phylogenetically ancient means of initiating tissue repair. The means and mechanisms of complement-mediated tissue repair are discussed in this review. There is increasing evidence that complement activation contributes to tissue repair at several levels. These range from the chemo-attraction of stem and progenitor cells to areas of complement activation, to increased survival of various cell types in the presence of split products of complement, and to the production of trophic factors by cells activated by the anaphylatoxins C3a and C5a. This repair aspect of complement biology has not found sufficient appreciation until recently. The following will examine this aspect of complement biology with an emphasis on the anaphylatoxins C3a and C5a.

The role of C1q in recognition of apoptotic epithelial cells and inflammatory cytokine production by phagocytes during Helicobacter pylori infection

Background

Gastric epithelial cells (GECs) undergo apoptosis during H. pylori infection and phagocytes within the mucosa engulf these cells. The recognition and clearance of apoptotic cells is a multifactorial process, enhanced by the presence of various bridging molecules and opsonins which are abundant in serum. However, it is not clear how recognition or clearance may differ in the context of H. pylori infection induced apoptosis. In addition, efferocytosis of sterile apoptotic cells is known to confer anti-inflammatory properties in the engulfing phagocyte, however it is unknown if this is maintained when phagocytes encounter H. pylori-infected cells. Thus, the ability of macrophages to bind and engulf gastric epithelial cells rendered apoptotic by H. pylori infection and the association of these interactions to the modulation of phagocyte inflammatory responses was investigated in the absence and presence of serum with a particular focus on the role of serum protein C1q.

Methods

Control (uninfected) or H. pylori-infected AGS cells were co-cultured with THP-1 macrophages in the presence or absence of serum or serum free conditions + C1q protein (40–80 μg/mL). Binding of AGS cells to THP-1 macrophages was assessed by microscopy and cytokine (IL-6 and TNF-α) release from LPS stimulated THP-1 macrophages was quantified by ELISA.

Results

We show that macrophages bound preferentially to cells undergoing apoptosis subsequent to infection with H. pylori. Binding of apoptotic AGS to THP-1 macrophages was significantly inhibited when studied in the absence of serum and reconstitution of serum-free medium with purified human C1q restored binding of macrophages to apoptotic cells. Co-culture of sterile apoptotic and H. pylori-infected AGS cells both attenuated LPS-stimulated cytokine production by THP-1 macrophages. Further, direct treatment of THP-1 macrophages with C1q attenuated LPS stimulated TNF-α production.

Conclusions

These studies suggest that C1q opsonizes GECs rendered apoptotic by H. pylori. No differences existed in the ability of infected or sterile apoptotic cells to attenuate macrophage cytokine production, however, there may be a direct role for C1q in modulating macrophage inflammatory cytokine production to infectious stimuli.

Electronic supplementary material

The online version of this article (doi:10.1186/s12950-015-0098-8) contains supplementary material, which is available to authorized users.

Complement factors C1q, C3 and C5b-9 in the posterior sclera of guinea pigs with negative lens-defocused myopia

AIM

To investigate the expression of complement factors in the posterior scleral fibroblasts of guinea pigs with negative lens-defocused myopia.

METHODS

Eighteen guinea pigs were assigned randomly to two groups: the negative lens-defocused group (NLD group, n=9) and the normal control without treatment group (NC group, n=9). The effect of myopic induction was compared in three subgroups: eyes treated with a -10.00 D negative lens in the NLD group (NL group), eyes treated with a plano (0 D) lens in the NLD group (PL group), and untreated right eyes in the NC group (NC group). The following analyses were conducted at four weeks: examination of the refractive error via retinoscopy, assessment of complement C5b-9 expression in the posterior scleral fibroblasts using immunohistochemistry, and measurements of complement C1q and C3 protein levels in the posterior sclera by Western blot.

RESULTS

After an induction period of four weeks, a significant myopic shift was detected in the eyes of the NL group, relative to that of the PL and NC groups (P<0.05). Data analysis showed a significant increase in the percentage of C5b-9 immunopositive fibroblasts in the posterior sclera of the NL group eyes, compared to the PL group (q=11.50, P<0.001). Significantly higher levels of C1q (q=4.94, P=0.01) and C3 (q=4.07, P=0.03) protein were detected in the posterior sclera of NL group eyes, compared to the PL group. There were no significant difference between the PL and NC groups for C5b-9 (q=2.44, P=0.10), C1q (q=1.55, P=0.53) and C3 (q=0.98, P=0.77) in the posterior sclera.

CONCLUSION

The data from present study provide evidence of the up-regulation of C5b-9, C1q and C3 in the posterior scleral fibroblasts in a NLD myopic animal model. The results suggest that the complement system may be involved in the development of myopia.

The paradoxical roles of C1q and C3 in autoimmunity

In this review we will focus on the links between complement and autoimmune diseases and will highlight how animal models have provided insights into the manner by which C1q and C3 act to modulate both adaptive and innate immune responses. In particular we will highlight how C1q may not only act as initiator of the classical complement pathway, but can also mediate multiple immune responses in a complement activation independent manner.

sghC1q, a novel C1q family member from half-smooth tongue sole (Cynoglossus semilaevis): identification, expression and analysis of antibacterial and antiviral activities

The C1q family includes many proteins that contain a globular (gC1q) domain, and this family is widely conserved from bacteria to mammals. The family is divided into three subgroups: C1q, C1q-like and ghC1q. In this study, a novel C1q family member, sghC1q, was cloned and identified from Cynoglossus semilaevis (named CssghC1q). The full-length CssghC1q cDNA spans 905 bp, including an open reading frame (ORF) of 768 bp, a 5'-untranslated region (UTR) of 25 bp and a 3'-UTR of 112 bp. The ORF encodes a putative protein of 255 amino acids (aa) with a deduced molecular weight of 28 kDa. The predicted protein contains a signal peptide (aa 1-19), a coiled-coil region (aa 61-102) and a globular C1q (gC1q) domain (aa 117-255). Protein sequence alignment indicated that the C-terminus of CssghC1q is highly conserved across several species. Phylogenetic analysis indicated that CssghC1q is most closely related to Maylandia zebra C1q-like-2-like. The CssghC1q genomic sequence spanned 1562 bp, with three exons and two introns. CssghC1q is constitutively expressed in all evaluated tissues, with the highest expression in the liver and the weakest in the heart. After a challenge with Vibrio anguillarum, CssghC1q transcript levels exhibited distinct time-dependent response patterns in the blood, head kidney, skin, spleen, intestine and liver. Recombinant CssghC1q protein exhibited antimicrobial activities against Gram-negative bacteria, Gram-positive bacteria and viruses. The minimum inhibitory concentration (MIC) values against Vibrio harveyi, Vibrio anguillarum, Pseudomonas aeruginosa and Staphylococcus aureus were 0.043 mg/mL, 0.087 mg/mL, 0.174 mg/mL and 0.025 mg/mL, respectively. A low concentration (0.06 mg/mL) of CssghC1q showed significant antiviral activity in vitro against nervous necrosis virus (NNV). These results suggest that CssghC1q plays a vital role in immune defense against bacteria and viruses.

Complement and spinal cord injury: traditional and non-traditional aspects of complement cascade function in the injured spinal cord microenvironment

The pathology associated with spinal cord injury (SCI) is caused not only by primary mechanical trauma, but also by secondary responses of the injured CNS. The inflammatory response to SCI is robust and plays an important but complex role in the progression of many secondary injury-associated pathways. Although recent studies have begun to dissect the beneficial and detrimental roles for inflammatory cells and proteins after SCI, many of these neuroimmune interactions are debated, not well understood, or completely unexplored. In this regard, the complement cascade is a key component of the inflammatory response to SCI, but is largely underappreciated, and our understanding of its diverse interactions and effects in this pathological environment is limited. In this review, we discuss complement in the context of SCI, first in relation to traditional functions for complement cascade activation, and then in relation to novel roles for complement proteins in a variety of models.

Complement protein C1q promotes macrophage anti-inflammatory M2-like polarization during the clearance of atherogenic lipoproteins

OBJECTIVE

Innate immune protein C1q plays a dual role in the chronic inflammatory disease of atherosclerosis. Complement activation via C1q exacerbates pathology in the atherosclerotic lesion in later stages of the disease. However, in early stages of disease C1q is protective. We hypothesize that complement-independent activities of C1q are involved in reprogramming macrophage inflammatory polarization.

METHODS

The influence of C1q on macrophage inflammatory responses during clearance of oxLDL was examined. Changes in cytokines at the gene and protein level were measured by quantitative PCR and ELISA assay.

RESULTS

C1q modulated cytokine expression in Raw264.7 macrophages during ingestion of oxLDL. Levels of pro-inflammatory cytokines IL-1β and IL-6 were downregulated by C1q, whereas levels of the anti-inflammatory cytokine IL-10 were increased. In addition, data from an NFκB-luciferase gene reporter assay suggest that C1q suppresses activation of NFκB during lipoprotein clearance in macrophages, providing one mechanism by which C1q downregulates pro-inflammatory cytokine production.

CONCLUSIONS

C1q-polarization of macrophages toward an anti-inflammatory (M2-like) phenotype may be important in dampening inflammation in the early atherosclerotic lesion. Further investigation of molecular pathways targeted by C1q may provide novel therapeutic targets for this disease.

Exploring the potential benefits of vaccinia virus complement control protein in controlling complement activation in pathogenesis of the central nervous system diseases

Aging is a major risk factor for the development of diseases related to the central nervous system (CNS), such as Alzheimer's disease (AD) and age-related macular degeneration (AMD). In both cases, linkage studies and genome-wide association studies found strong links with complement regulatory genes and disease risk. In AD, both CLU and CR1 genes were implicated in the late-onset form of the disease. In AMD, polymorphisms in CFH, CFB and C2 were similarly implicated. The cost of caring for patients with AD or AMD is approaching billions of dollars, and with the baby boomers reaching their 60's, this amount is likely to increase further. Intervention using complement inhibitors for individuals in their early 50s who are at a higher risk of disease development, (testing positive for genetic risk factors), could slow the progression of AD or AMD and possibly prevent the severity of late stage symptoms. Although we have used the vaccinia virus complement control protein (VCP) to elucidate the role of complement in CNS diseases, it has merely been an investigational tool but not the only possible potential therapeutic agent.

Serum mannose-binding lectin and C-reactive protein are potential biomarkers for patients with community-acquired pneumonia

AIM

The aim of this study was to identify whether mannose-binding lectin (MBL) and C-reactive protein (CRP) may be used as clinical biomarkers for predicting outcome of community-acquired pneumonia (CAP) by tracking serum MBL and CRP level changes during a time course.

METHODS

One hundred four patients with CAP and 100 healthy individuals were enrolled in this study. The patients were further divided into Survivor and Death groups based on 30-day mortality. The MBL and CRP levels in these patients at pre- and post-treatments at days 4 and 7 were determined using an immunoturbidimetric assay and an enzyme-linked immunosorbent assay (ELISA).

RESULTS

Compared to the control group, the MBL and CRP levels in the CAP group were significantly higher. CRP levels in the CAP group significantly reduced within 1 week following anti-infection and other supporting therapies including anti-phlegm and liquidation. MBL levels were significantly higher in the Survivor group than in the Death group (p<0.05). On the contrary, CRP levels were significantly higher in the Death group than in the Survivor group (p<0.05). There was a negative correlation between the serum MBL and CRP levels in all patients following the treatments.

CONCLUSION

Both the MBL and CRP can serve as inflammatory markers in predicting the outcome of patients with CAP.

Complement protein C1q and adiponectin stimulate Mer tyrosine kinase-dependent engulfment of apoptotic cells through a shared pathway

The failure to clear apoptotic cells is linked to defects in development and autoimmunity. Complement component C1q is required for efficient engulfment of apoptotic cells (efferocytosis), and C1q deficiency leads to the development of lupus. We recently identified a novel molecular mechanism for C1q-dependent efferocytosis in murine macrophages. C1q elicited the expression of Mer tyrosine kinase (Mer), a receptor that regulates efficient efferocytosis and prevention of autoimmunity. To characterize the C1q-dependent signal transduction mechanism, pathway analysis of the transcriptome from C1q-activated macrophages was performed, and it identified the adiponectin signaling pathway as significantly upregulated with C1q. Adiponectin is structurally homologous to C1q and regulates cellular metabolism via downstream activation of 5'adenosine monophosphate-activated protein kinase (AMPK). Macrophage stimulation with C1q resulted in the activation of AMPK, and silencing of AMPK expression using siRNA-inhibited C1q-dependent efferocytosis. Adiponectin signaling also stimulates activation of nuclear receptors, and inhibition of the nuclear receptor retinoid X receptor abrogated C1q-dependent Mer expression and efferocytosis. Furthermore, adiponectin elicited Mer expression and Mer-dependent efferocytosis in macrophages similar to cells stimulated with C1q. Collectively, our results suggest that C1q and adiponectin share a common signal transduction cascade to promote clearance of apoptotic cells, and identify a novel molecular pathway required for efficient efferocytosis.

A novel C1q-domain-containing (C1qDC) protein from Mytilus coruscus with the transcriptional analysis against marine pathogens and heavy metals

The C1q-domain-containing (C1qDC) proteins, which are involved in various processes of vertebrates, are important pattern recognition receptors in innate immunity of invertebrates. In present study, a novel C1qDC was identified from Mytilus coruscus (designated as McC1qDC), which was 917 bp in length encoding 236 amino acids with a typical signal peptide of 19 amino acid residues in N-terminus. Based on its conserved C1q domain and molecular architecture of 10 β-strand jelly-roll folding topology structure, McC1qDC might be classified as a member of the C1q family. The mRNA transcript of McC1qDC was predominantly detectable in the hemocytes, and a less degree in gill, gonad and mantle, but trace in foot, adductor and digestive gland. Upon induction by Vibrio harveyi and Vibrio alginolyticus, McC1qDC expression was significantly up-regulated. Time-dependent mRNA expression of McC1qDC was found during copper and cadmium exposure for its heavy metal-binding domain. These results indicated that McC1qDC was a novel member of the C1qDC protein family as a pattern recognition receptor against pathogens, and might be developed as a potential indicator for monitoring heavy metals pollution.

Calreticulin contributes to C1q-dependent recruitment of microglia in the leech Hirudo medicinalis following a CNS injury

Background

The medicinal leech is considered as a complementary and appropriate model to study immune functions in the central nervous system (CNS). In a context in which an injured leech’s CNS can naturally restore normal synaptic connections, the accumulation of microglia (immune cells of the CNS that are exclusively resident in leeches) has been shown to be essential at the lesion to engage the axonal sprouting. HmC1q (Hm for Hirudo medicinalis) possesses chemotactic properties that are important in the microglial cell recruitment by recognizing at least a C1q binding protein (HmC1qBP alias gC1qR).

Material/Methods

Recombinant forms of C1q were used in affinity purification and in vitro chemotaxis assays. Anti-calreticulin antibodies were used to neutralize C1q-mediated chemotaxis and locate the production of calreticulin in leech CNS.

Results

A newly characterized leech calreticulin (HmCalR) has been shown to interact with C1q and participate to the HmC1q-dependent microglia accumulation. HmCalR, which has been detected in only some microglial cells, is consequently a second binding protein for HmC1q, allowing the chemoattraction of resident microglia in the nerve repair process.

Conclusions

These data give new insight into calreticulin/C1q interaction in an immune function of neuroprotection, suggesting another molecular target to use in investigation of microglia reactivity in a model of CNS injury.

Increased complement C1q level marks active disease in human tuberculosis

Background

Complement functions as an important host defense system and complement C5 and C7 have been implicated in immunopathology of tuberculosis. However, little is known about the role of other complement components in tuberculosis.

Methods

Complement gene expression in peripheral blood mononuclear cells of tuberculosis patients and controls were determined using whole genome transcriptional microarray assays. The mRNA and protein levels of three C1q components, C1qA, C1qB, and C1qC, were further validated by qRT-PCR and enzyme-linked immunosorbent assay, respectively. The percentages of C1q expression in CD14 positive cells were determined by flow cytometry. Finally, C1qC protein level was quantified in the pleural fluid of tuberculosis and non-tuberculosis pleurisy.

Results

C1q expression increases significantly in the peripheral blood of patients with active tuberculosis compared to healthy controls and individuals with latent TB infection. The percentage of C1q-expressing CD14 positive cells is significantly increased in active TB patients. C1q expression in the peripheral blood correlates with sputum smear positivity in tuberculosis patients and is reduced after anti-tuberculosis chemotherapy. Notably, receiver operating characteristic analysis showed that C1qC mRNA levels in peripheral blood efficiently discriminate active from latent tuberculosis infection and healthy controls. Additionally, C1qC protein level in pleural effusion shows improved power in discriminating tuberculosis from non-tuberculosis pleurisy when compared to other inflammatory markers, such as IL-6 and TNF-α.

Conclusions

C1q expression correlates with active disease in human tuberculosis. C1q could be a potential diagnostic marker to discriminate active tuberculosis from latent tuberculosis infection as well as tuberculosis pleurisy from non-tuberculosis pleurisy.

The lectin pathway of complement and rheumatic heart disease

The innate immune system is the first line of host defense against infection and is comprised of humoral and cellular mechanisms that recognize potential pathogens within minutes or hours of entry. The effector components of innate immunity include epithelial barriers, phagocytes, and natural killer cells, as well as cytokines and the complement system. Complement plays an important role in the immediate response against microorganisms, including Streptococcus sp. The lectin pathway is one of three pathways by which the complement system can be activated. This pathway is initiated by the binding of mannose-binding lectin (MBL), collectin 11 (CL-K1), and ficolins (Ficolin-1, Ficolin-2, and Ficolin-3) to microbial surface oligosaccharides and acetylated residues, respectively. Upon binding to target molecules, MBL, CL-K1, and ficolins form complexes with MBL-associated serine proteases 1 and 2 (MASP-1 and MASP-2), which cleave C4 and C2 forming the C3 convertase (C4b2a). Subsequent activation of complement cascade leads to opsonization, phagocytosis, and lysis of target microorganisms through the formation of the membrane-attack complex. In addition, activation of complement may induce several inflammatory effects, such as expression of adhesion molecules, chemotaxis and activation of leukocytes, release of reactive oxygen species, and secretion of cytokines and chemokines. In this chapter, we review the general aspects of the structure, function, and genetic polymorphism of lectin-pathway components and discuss most recent understanding on the role of the lectin pathway in the predisposition and clinical progression of Rheumatic Fever.

Three complement component 1q genes from rock bream, Oplegnathus fasciatus: genome characterization and potential role in immune response against bacterial and viral infections

Complement component 1q (C1q) is a subcomponent of the C1 complex and the key protein that recognizes and binds to a broad range of immune and non-immune ligands to initiate the classical complement pathway. In the present study, we identified and characterized three novel C1q family members from rock bream, Oplegnathus fasciatus. The full-length cDNAs of C1q A-like (RbC1qAL), C1q B-like (RbC1qBL), and C1q C-like (RbC1qCL) consist of 780, 720 and 726 bp of nucleotide sequence encoding polypeptides of 260, 240 and 242 amino acids, respectively. All three RbC1qs possess a leading signal peptide and collagen-like region(s) (CLRs) in the N-terminus, and a C1q domain at the C-terminus. The C1q characteristic Gly-X-Y repeats are present in all three RbC1qs, while the CLR-associated sequence that enhances phagocytic activity is present in RbC1qAL ((49)GEKGEP(54)) and RbC1qCL ((70)GEKGEP(75)). Moreover, the coding region was distributed across six exons in RbCqAL and RbC1qCL, but only five exons in RbC1qBL. Phylogenetic analysis revealed that the three RbC1qs tightly cluster with the fish clade. All three RbC1qs are most highly expressed in the spleen and liver, as indicated by qPCR tissue profiling. In addition, all three are transcriptionally responsive to immune challenge, with liver expression being significantly up-regulated in the early phase of infection with intact, live bacteria (Edwardsiella tarda and Streptococcus iniae) and virus (rock bream iridovirus) and in the late phase of exposure to purified endotoxin (lipopolysaccharide). These data collectively suggest that the RbC1qs may play defense roles as an innate immune response to protect the rock bream from bacterial and viral infections.

C1q induction and global complement pathway activation do not contribute to ALS toxicity in mutant SOD1 mice

Accumulating evidence from mice expressing ALS-causing mutations in superoxide dismutase (SOD1) has implicated pathological immune responses in motor neuron degeneration. This includes microglial activation, lymphocyte infiltration, and the induction of C1q, the initiating component of the classic complement system that is the protein-based arm of the innate immune response, in motor neurons of multiple ALS mouse models expressing dismutase active or inactive SOD1 mutants. Robust induction early in disease course is now identified for multiple complement components (including C1q, C4, and C3) in spinal cords of SOD1 mutant-expressing mice, consistent with initial intraneuronal C1q induction, followed by global activation of the complement pathway. We now test if this activation is a mechanistic contributor to disease. Deletion of the C1q gene in mice expressing an ALS-causing mutant in SOD1 to eliminate C1q induction, and complement cascade activation that follows from it, is demonstrated to produce changes in microglial morphology accompanied by enhanced loss, not retention, of synaptic densities during disease. C1q-dependent synaptic loss is shown to be especially prominent for cholinergic C-bouton nerve terminal input onto motor neurons in affected C1q-deleted SOD1 mutant mice. Nevertheless, overall onset and progression of disease are unaffected in C1q- and C3-deleted ALS mice, thus establishing that C1q induction and classic or alternative complement pathway activation do not contribute significantly to SOD1 mutant-mediated ALS pathogenesis in mice.

Systematic identification of trans eQTLs as putative drivers of known disease associations

Identifying the downstream effects of disease-associated SNPs is challenging. To help overcome this problem, we performed expression quantitative trait locus (eQTL) meta-analysis in non-transformed peripheral blood samples from 5,311 individuals with replication in 2,775 individuals. We identified and replicated trans eQTLs for 233 SNPs (reflecting 103 independent loci) that were previously associated with complex traits at genome-wide significance. Some of these SNPs affect multiple genes in trans that are known to be altered in individuals with disease: rs4917014, previously associated with systemic lupus erythematosus (SLE), altered gene expression of C1QB and five type I interferon response genes, both hallmarks of SLE. DeepSAGE RNA sequencing showed that rs4917014 strongly alters the 3' UTR levels of IKZF1 in cis, and chromatin immunoprecipitation and sequencing analysis of the trans-regulated genes implicated IKZF1 as the causal gene. Variants associated with cholesterol metabolism and type 1 diabetes showed similar phenomena, indicating that large-scale eQTL mapping provides insight into the downstream effects of many trait-associated variants.

The role of the innate immune system in Alzheimer's disease and frontotemporal lobar degeneration: an eye on microglia

In the last few years, genetic and biomolecular mechanisms at the basis of Alzheimer's disease (AD) and frontotemporal lobar degeneration (FTLD) have been unraveled. A key role is played by microglia, which represent the immune effector cells in the central nervous system (CNS). They are extremely sensitive to the environmental changes in the brain and are activated in response to several pathologic events within the CNS, including altered neuronal function, infection, injury, and inflammation. While short-term microglial activity has generally a neuroprotective role, chronic activation has been implicated in the pathogenesis of neurodegenerative disorders, including AD and FTLD. In this framework, the purpose of this review is to give an overview of clinical features, genetics, and novel discoveries on biomolecular pathogenic mechanisms at the basis of these two neurodegenerative diseases and to outline current evidence regarding the role played by activated microglia in their pathogenesis.

Expression of recombinant human complement C1q allows identification of the C1r/C1s-binding sites

Complement C1q is a hexameric molecule assembled from 18 polypeptide chains of three different types encoded by three genes. This versatile recognition protein senses a wide variety of immune and nonimmune ligands, including pathogens and altered self components, and triggers the classical complement pathway through activation of its associated proteases C1r and C1s. We report a method for expression of recombinant full-length human C1q involving stable transfection of HEK 293-F mammalian cells and fusion of an affinity tag to the C-terminal end of the C chain. The resulting recombinant (r) C1q molecule is similar to serum C1q as judged from biochemical and structural analyses and exhibits the characteristic shape of a bunch of flowers. Analysis of its interaction properties by surface plasmon resonance shows that rC1q retains the ability of serum C1q to associate with the C1s-C1r-C1r-C1s tetramer, to recognize physiological C1q ligands such as IgG and pentraxin 3, and to trigger C1r and C1s activation. Functional analysis of rC1q variants carrying mutations of LysA59, LysB61, and/or LysC58, in the collagen-like stems, demonstrates that LysB61 and LysC58 each play a key role in the interaction with C1s-C1r-C1r-C1s, with LysA59 being involved to a lesser degree. We propose that LysB61 and LysC58 both form salt bridges with outer acidic Ca(2+) ligands of the C1r and C1s CUB (complement C1r/C1s, Uegf, bone morphogenetic protein) domains. The expression method reported here opens the way for deciphering the molecular basis of the unusual binding versatility of C1q by mapping the residues involved in the sensing of its targets and the binding of its receptors.

Research progress on the mollusc immunity in China

The economical and phylogenic importance of mollusc has led an increasing number of investigations giving emphasis to immune defense mechanism. This review discusses the advances in immunological study of mollusc in China, with special reference to dominant aquaculture species over the past decades. As an invertebrate group, molluscs lack adaptive immunity and consequently they have evolved sophisticated strategies of innate immunity for defense against pathogens. This review aims to present the various immunologically significant pattern recognition receptors (PRRs), such as Toll-like receptors (TLRs), lectins, lipopolysaccharide and β-1, 3-glucan binding protein (LGBP), scavenger receptors (SRs) employed by mollucans. This work also highlights immune proteolytic cascade, TLR signaling pathway and an extensive repertoire of immune effectors including antimicrobial peptide, lysozyme, antioxidant enzyme and heat shock protein. Further, the review presents the preliminary progress made on the catecholaminergic neuroendocrine system in scallop and its immunomodulation function to throw light into neuroendocrine-immune regulatory network in lower invertebrates.

C1q-induced LRP1B and GPR6 proteins expressed early in Alzheimer disease mouse models, are essential for the C1q-mediated protection against amyloid-β neurotoxicity

Complement protein C1q is induced in the brain in response to a variety of neuronal injuries, including Alzheimer disease (AD), and blocks fibrillar amyloid-β (fAβ) neurotoxicity in vitro. Here, we show that C1q protects immature and mature primary neurons against fAβ toxicity, and we report for the first time that C1q prevents toxicity induced by oligomeric forms of amyloid-β (Aβ). Gene expression analysis reveals C1q-activated phosphorylated cAMP-response element-binding protein and AP-1, two transcription factors associated with neuronal survival and neurite outgrowth, and increased LRP1B and G protein-coupled receptor 6(GPR6) expression in fAβ-injured neurons. Silencing of cAMP-response element-binding protein, LRP1B or GPR6 expression inhibited C1q-mediated neuroprotection from fAβ-induced injury. In addition, C1q altered the association of oligomeric Aβ and fAβ with neurons. In vivo, increased hippocampal expression of C1q, LRP1B, and GPR6 is observed as early as 2 months of age in the 3 × Tg mouse model of AD, whereas no such induction of LRP1B and GPR6 was seen in C1q-deficient AD mice. In contrast, expression of C1r and C1s, proteases required to activate the classical complement pathway, and C3 showed a significant age-dependent increase only after 10-13 months of age when Aβ plaques start to accumulate in this AD model. Thus, our results identify pathways by which C1q, up-regulated in vivo early in response to injury without the coordinate induction of other complement components, can induce a program of gene expression that promotes neuroprotection and thus may provide protection against Aβ in preclinical stages of AD and other neurodegenerative processes.

MAPK phosphatase-1 is required for regulatory natural autoantibody-mediated inhibition of TLR responses

Naturally arising IgM antibodies, which recognize neo-determinants on apoptotic cell (AC) membranes, are present from birth and can be further induced by AC challenge. Such naturally arising IgM antibodies can suppress proinflammatory responses to purified agonists for Toll-like receptors (TLRs), as well as block the induction of IgG immune complex-induced in vitro and in vivo pathogenic responses. To investigate the responsible mechanisms, we studied the regulatory effects of IgM anti-AC antibody on responses in bone marrow-derived dendritic cells mediated by a range of different TLRs and found that addition of IgM anti-AC inhibited the activation of the primary MAPKs: ERK1/2, JNK, and particularly p38. This was dependent on the recruitment of either C1q or mannose-binding lectin, which are both early complement factors that tag ACs for innate immune recognition. Strikingly, MAPK inhibition of responses to TLR agonists, and to lupus IgG autoantibody-chromatin immune complexes, was found to correlate with, and had an absolute requirement for, the induction and nuclear localization of MAPK phosphatase-1, a factor known to mediate glucocorticoid suppression of immune responses. Further experiments showed that natural IgM antibodies in serum exhibited the same inhibitory properties. These studies elucidate a novel homeostatic pathway by which natural antibodies, which are products of the adaptive immune system, can directly blunt inflammatory responses by recruitment and coordination of a primitive regulatory pathway of the innate immune system.

The alternative complement pathway propagates inflammation and injury in murine ischemic stroke

There is mounting evidence indicating an important role for complement in the pathogenesis of cerebral ischemia-reperfusion injury, or ischemic stroke. The role of the alternative complement pathway in ischemic stroke has not been investigated, and there is conflicting data on the role of the terminal pathway. In this study, we show that compared with wild-type mice, mice deficient in the alternative pathway protein factor B or mice treated with the alternative pathway inhibitor CR2-fH have improved outcomes after 60-min middle cerebral artery occlusion and 24-h reperfusion. Factor B-deficient or CR2-fH-treated mice were protected in terms of improved neurologic function and reduced cerebral infarct, demyelination, P-selectin expression, neutrophil infiltration, and microthrombi formation. Mice deficient in both the classical and lectin pathways (C1q/MBL deficient) were also protected from cerebral ischemia-reperfusion injury, and there was no detectable C3d deposition in the ipsilateral brain of these mice. These data demonstrate that the alternative pathway is not alone sufficient to initiate complement activation and indicate that the alternative pathway propagates cerebral injury via amplification of the cascade. Deficiency of C6, a component of the terminal cytolytic membrane attack complex, had no effect on outcome after ischemic stroke, indicating that the membrane attack complex is not involved in mediating injury in this model. We additionally show that the protective effect of factor B deficiency and CR2-fH treatment is sustained in the subacute stage of infarct development, adding to the clinical relevance of these findings.

A novel C1qDC protein acting as pattern recognition receptor in scallop Argopecten irradians

The C1q domain containing (C1qDC) proteins refer to a family of proteins containing the versatile charge pattern recognition globular C1q domain in the C-terminus, which could bind various ligands including PAMPs and trigger a serial of immune response. In this study, a novel C1qDC protein was identified from Argopecten irradians (designated as AiC1qDC-2). Its full-length cDNA was of 1062 bp with an open reading frame of 720 bp encoding a polypeptide of 240 amino acids containing a typical gC1q domain. This gC1q domain possessed the typical 10-stranded β-sandwich fold with a jelly-roll topology common to all C1q family members, and shared high homology with most of the other identified gC1q domains. The mRNA transcripts of AiC1qDC-2 were mainly detected in hepatopancreas, and also marginally detectable in mantle, gonad, adductor, gill and hemocytes. Its relative expression level in hemocytes was significantly up-regulated after challenges of fungi Pichia pastoris GS115 (P < 0.05), Gram-positive bacteria Micrococcus luteus (P < 0.05) and Gram-negative bacteria Vibrio anguillarum (P < 0.05). The recombinant protein of AiC1qDC-2 (rAiC1qDC-2) could bind various PAMPs, including LPS, PGN, polyI:C, mannan, β-1,3-glucan as well as Yeast-glucan, and displayed agglutinating activity to fungi P. pastoris GS115, Gram-positive bacteria Bacillus subtilis and Gram-negative bacteria Escherichia coli TOP10F' as well as V. anguillarum. All these results indicated that AiC1qDC-2 could function as a pattern recognition receptor to recognize various PAMPs on different pathogens in the innate immune responses of scallop, and provided new clues to understand the role of invertebrate C1qDC proteins in the ancient complement system.

Increased plasma mannose binding lectin levels are associated with bronchiolitis obliterans after lung transplantation

Background

Long-term lung allograft survival is limited by bronchiolitis obliterans syndrome (BOS). Mannose binding lectin (MBL) belongs to the innate immune system, participates in complement activation, and may predispose to graft rejection. We investigated mannose binding (MBL) during cold ischemia and in tissue samples from explanted lungs with BOS, and assessed MBL and complement proteins in plasma post-lung transplantation relative to BOS staging.

Methods

MBL was detected by immunohistochemistry lung tissue at the time of cold ischemia and in samples with BOS. MBL was assayed in the peripheral blood of 66 lung transplant patients transplanted between 1990–2007.

Results

MBL localized to vasculature and basement membrane during cold ischemia and BOS. Patients further out post-lung transplant > 5 years (n = 33), had significantly lower levels of MBL in the blood compared to lung transplant patients < 5 years with BOS Op-3 (n = 17), 1738 ± 250 ng/ml vs 3198 ± 370 ng/ml, p = 0.027, and similar levels to lung transplant patients < 5 years with BOS 0 (n = 16), 1738 ± 250 ng/ml vs 1808 ± 345 ng/ml. MBL levels in all BOS 0 (n = 30) vs. all BOS Op-3 (n = 36) were 1378 ± 275 ng/ml vs. 2578 ± 390 ng/ml, p = 0.001, respectively. C3 plasma levels in BOS 0 (n = 30) vs. BOS Op-3 (n = 36) were 101 ± 19.8 mg/ml vs. 114 ± 25.2 mg/ml, p = 0.024, respectively.

Conclusions

MBL localizes within the lung during graft ischemia and BOS, higher levels of plasma MBL are associated with BOS Op-3 and < 5 years post-transplant, and higher level of plasma complement protein C3 was associated with BOS Op-3 clinical status. MBL may serve as a biomarker for poorer outcome post-lung transplantation.

Heavy chains of inter alpha inhibitor (IαI) inhibit the human complement system at early stages of the cascade

Inter alpha inhibitor (IαI) is an abundant serum protein consisting of three polypeptides: two heavy chains (HC1 and HC2) and bikunin, a broad-specificity Kunitz-type proteinase inhibitor. The complex is covalently held together by chondroitin sulfate but during inflammation IαI may interact with TNF-stimulated gene 6 protein (TSG-6), which supports transesterification of heavy chains to hyaluronan. Recently, IαI was shown to inhibit mouse complement in vivo and to protect from complement-mediated lung injury but the mechanism of such activity was not elucidated. Using human serum depleted from IαI, we found that IαI is not an essential human complement inhibitor as was reported for mice and that such serum has unaltered hemolytic activity. However, purified human IαI inhibited classical, lectin and alternative complement pathways in vitro when added in excess to human serum. The inhibitory activity was dependent on heavy chains but not bikunin and detected at the level of initiating molecules (MBL, properdin) in the lectin/alternative pathways or C4b in the classical pathway. Furthermore, IαI affected formation and assembly of the C1 complex and prevented assembly of the classical pathway C3-convertase. Presence and putative interactions with TSG-6 did not affect the ability of IαI to inhibit complement thus implicating IαI as a potentially important complement inhibitor once enriched onto hyaluronan moieties in the course of local inflammatory processes. In support of this, we found a correlation between IαI/HC-containing proteins and hemolytic activity of synovial fluid from patients suffering from rheumatoid arthritis.

Complement protein C1q directs macrophage polarization and limits inflammasome activity during the uptake of apoptotic cells

Deficiency in C1q, the recognition component of the classical complement cascade and a pattern recognition receptor involved in apoptotic cell clearance, leads to lupus-like autoimmune diseases characterized by auto-antibodies to self proteins and aberrant innate immune cell activation likely due to impaired clearance of apoptotic cells. In this study, we developed an autologous system using primary human lymphocytes and human monocyte-derived macrophages (HMDMs) to characterize the effect of C1q on macrophage gene expression profiles during the uptake of apoptotic cells. C1q bound to autologous apoptotic lymphocytes modulated expression of genes associated with JAK/STAT signaling, chemotaxis, immunoregulation, and NLRP3 inflammasome activation in LPS-stimulated HMDMs. Specifically, C1q sequentially induced type I IFNs, IL-27, and IL-10 in LPS-stimulated HMDMs and IL-27 in HMDMs when incubated with apoptotic lymphocyte conditioned media. Coincubation with C1q tails prevented the induction of type I IFNs and IL-27 in a dose-dependent manner, and neutralization of type I IFNs partially prevented IL-27 induction by C1q. Finally, C1q decreased procaspase-1 cleavage and caspase-1-dependent cleavage of IL-1β suggesting a potent inhibitory effect of C1q on inflammasome activation. These results identify specific molecular pathways induced by C1q to suppress macrophage inflammation and provide potential therapeutic targets to control macrophage polarization and thus inflammation and autoimmunity.

A review: inflammatory process in Alzheimer's disease, role of cytokines

Alzheimer's disease (AD) is the most common neurodegenerative disorder to date. Neuropathological hallmarks are β-amyloid (Aβ) plaques and neurofibrillary tangles, but the inflammatory process has a fundamental role in the pathogenesis of AD. Inflammatory components related to AD neuroinflammation include brain cells such as microglia and astrocytes, the complement system, as well as cytokines and chemokines. Cytokines play a key role in inflammatory and anti-inflammatory processes in AD. An important factor in the onset of inflammatory process is the overexpression of interleukin (IL)-1, which produces many reactions in a vicious circle that cause dysfunction and neuronal death. Other important cytokines in neuroinflammation are IL-6 and tumor necrosis factor (TNF)-α. By contrast, other cytokines such as IL-1 receptor antagonist (IL-1ra), IL-4, IL-10, and transforming growth factor (TGF)-β can suppress both proinflammatory cytokine production and their action, subsequently protecting the brain. It has been observed in epidemiological studies that treatment with nonsteroidal anti-inflammatory drugs (NSAIDs) decreases the risk for developing AD. Unfortunately, clinical trials of NSAIDs in AD patients have not been very fruitful. Proinflammatory responses may be countered through polyphenols. Supplementation of these natural compounds may provide a new therapeutic line of approach to this brain disorder.

Relevance of the lectin pathway of complement in rheumatic diseases

Due to its importance both in the clearance of pathogens that contribute as rheumatic etiological agents and in the disposal of apoptotic bodies and potential autoimmune initiators, deficiencies of the components of the lectin pathway of complement have been found to increase susceptibility and modulate the severity of most rheumatic disorders. This chapter introduces the general aspects of the structure, function, and genetics of lectin pathway components and summarizes current knowledge of the field regarding rheumatic diseases predisposition and modulation.

Complement component C1q regulates macrophage expression of Mer tyrosine kinase to promote clearance of apoptotic cells

Failure to efficiently clear apoptotic cells is linked to defects in development and the onset of autoimmunity. Complement component C1q is required for efficient engulfment of apoptotic cells in mice and humans; however, the molecular mechanisms leading to C1q-dependent engulfment are not fully understood. In this study, we used primary mouse macrophages to identify and characterize a novel molecular mechanism for macrophage-mediated C1q-dependent engulfment of apoptotic cells. We found that macrophage activation with C1q resulted in cycloheximide-sensitive enhanced engulfment, indicating a requirement for de novo protein synthesis. To investigate the cycloheximide-sensitive pathway, C1q-elicited macrophage transcripts were identified by microarray. C1q triggered the expression of Mer tyrosine kinase (Mer) and the Mer ligand growth arrest-specific 6: a receptor-ligand pair that mediates clearance of apoptotic cells. Full-length native C1q, and not the collagen-like tail or heat-denatured protein, stimulated Mer expression. This novel pathway is specific to C1q because mannose-binding lectin, a related collectin, failed to upregulate Mer expression and function. Soluble Mer-Fc fusion protein inhibited C1q-dependent engulfment of apoptotic cells, indicating a requirement for Mer. Moreover, Mer-deficient macrophages failed to respond to C1q with enhanced engulfment. Our results suggest that C1q elicits a macrophage phenotype specifically tailored for apoptotic cell clearance, and these data are consistent with the established requirement for C1q in prevention of autoimmunity.

Defective activities, but not secretions, resulting from gene point mutations of human mannan-binding lectin

Human mannan-binding lectin (MBL) plays a pivotal role in innate immunity. Substantial literature supports the belief that three point mutations, CGT52TGT, GGC54GAC and GGA57GAA, in the collagen-like region (CLR) of the human MBL gene, are associated with increased susceptibility to infection, autoimmunity and carcinogenesis. To investigate the mechanisms of MBL deficiency, human wild-type and three variant MBL genes were expressed in COS-7 and Chinese hamster ovary (CHO) cells. Results showed that no apparent differences were found among the levels of gene transcription and protein secretion of four forms of MBL. However, the degree of oligomerization of variant forms of MBL was found to be much lower than that of recombinant human wild-type MBL. The ability of variant MBL proteins to bind mannan was much weaker than that of the wild-type MBL protein, and the MBL variants failed to effectively activate the complement lectin pathway. These data suggested that a lower order oligomer, but not decreased plasma levels of MBL, may be the main result of MBL gene mutations and may be associated with immunodeficiency.

Cell culture model that mimics drusen formation and triggers complement activation associated with age-related macular degeneration

We introduce a human retinal pigmented epithelial (RPE) cell-culture model that mimics several key aspects of early stage age-related macular degeneration (AMD). These include accumulation of sub-RPE deposits that contain molecular constituents of human drusen, and activation of complement leading to formation of deposit-associated terminal complement complexes. Abundant sub-RPE deposits that are rich in apolipoprotein E (APOE), a prominent drusen constituent, are formed by RPE cells grown on porous supports. Exposure to human serum results in selective, deposit-associated accumulation of additional known drusen components, including vitronectin, clusterin, and serum amyloid P, thus suggesting that specific protein-protein interactions contribute to the accretion of plasma proteins during drusen formation. Serum exposure also leads to complement activation, as evidenced by the generation of C5b-9 immunoreactive terminal complement complexes in association with APOE-containing deposits. Ultrastructural analyses reveal two morphologically distinct forms of deposits: One consisting of membrane-bounded multivesicular material, and the other of nonmembrane-bounded particle conglomerates. Collectively, these results suggest that drusen formation involves the accumulation of sub-RPE material rich in APOE, a prominent biosynthetic product of the RPE, which interacts with a select group of drusen-associated plasma proteins. Activation of the complement cascade appears to be mediated via the classical pathway by the binding of C1q to ligands in APOE-rich deposits, triggering direct activation of complement by C1q, deposition of terminal complement complexes and inflammatory sequelae. This model system will facilitate the analysis of molecular and cellular aspects of AMD pathogenesis, and the testing of new therapeutic agents for its treatment.

Subclinical rejection in renal transplants is associated with low serum mannose-binding lectin levels

Surveillance biopsies have contributed to the understanding of the natural history of renal allograft lesions. Subclinical rejection, defined as the presence of histological lesions, indistinguishable from acute rejection in stable grafts, is associated with progression of interstitial fibrosis and tubular atrophy. The prevalence of subclinical rejection has decreased as more powerful immunosuppressive treatments have been introduced, suggesting that subclinical rejection represents the degree of control of the alloimmune response. However, non-immune factors such as donor age are also associated with the prevalence of subclinical rejection, suggesting that kidneys from older donors are more susceptible to insult and have a reduced capacity for tissue regeneration. Innate immunity has a crucial role in the modulation of the inflammatory response during infection and tissue damage. Mannose-binding lectin (MBL) is an innate immune protein, the polymorphisms of which are associated with infection, low-grade inflammation, diabetes, and cardiovascular disease. However, the relationship between MBL and disease is complex. For example, low MBL level is associated with higher risk for diabetes, whereas in patients with diabetes, high MBL level is associated with more severe renal damage. In renal transplant patients, low MBL levels are associated with an increased prevalence of infection and diabetes, whereas high MBL levels are associated with shortened graft survival. Although MBL is not clearly associated with prevalence of acute rejection, surveillance biopsy studies have shown that low MBL levels are associated with subclinical rejection in kidney and the heart, suggesting that MBL modulates the injury–repair process of the allograft.

Complement in the brain

The brain is considered to be an immune privileged site, because the blood-brain barrier limits entry of blood borne cells and proteins into the central nervous system (CNS). As a result, the detection and clearance of invading microorganisms and senescent cells as well as surplus neurotransmitters, aged and glycated proteins, in order to maintain a healthy environment for neuronal and glial cells, is largely confined to the innate immune system. In recent years it has become clear that many factors of innate immunity are expressed throughout the brain. Neuronal and glial cells express Toll like receptors as well as complement receptors, and virtually all complement components can be locally produced in the brain, often in response to injury or developmental cues. However, as inflammatory reactions could interfere with proper functioning of the brain, tight and fine tuned regulatory mechanisms are warranted. In age related diseases, such as Alzheimer's disease (AD), accumulating amyloid proteins elicit complement activation and a local, chronic inflammatory response that leads to attraction and activation of glial cells that, under such activation conditions, can produce neurotoxic substances, including pro-inflammatory cytokines and oxygen radicals. This process may be exacerbated by a disturbed balance between complement activators and complement regulatory proteins such as occurs in AD, as the local synthesis of these proteins is differentially regulated by pro-inflammatory cytokines. Much knowledge about the role of complement in neurodegenerative diseases has been derived from animal studies with transgenic overexpressing or knockout mice for specific complement factors or receptors. These studies have provided insight into the potential therapeutic use of complement regulators and complement receptor antagonists in chronic neurodegenerative diseases as well as in acute conditions, such as stroke. Interestingly, recent animal studies have also indicated that complement activation products are involved in brain development and synapse formation. Not only are these findings important for the understanding of how brain development and neural network formation is organized, it may also give insights into the role of complement in processes of neurodegeneration and neuroprotection in the injured or aged and diseased adult central nervous system, and thus aid in identifying novel and specific targets for therapeutic intervention.

Specific detection of antibodies to different flaviviruses using a new immune complex ELISA

Immune complex (IC) ELISAs for IgG antibodies to various virus antigens have turned out to be both highly specific and sensitive. During incubation of a labelled antigen with the serum samples, ICs are formed, which bind to microtiter plates coated with rheumatoid factor (RF) IgM. Here, we describe an improved coating of the solid-phase support comparing various Fc-receptor molecules. IC ELISAs were applied to detect human IgG antibodies to the highly virus-specific ED3 domain of West Nile- and tick-borne encephalitis virus envelopes. Compared with other Fc-receptor molecules like RF or C1q, FcγRIIA (CD32) turned out to bind the ICs composed of IgG antibodies and peroxidase-labelled ED3 antigens more efficiently. Due to low background reactions, sera could be tested at a dilution of 1:10. Moreover, using CD32 instead of RF coating, anti-flavivirus antibodies could be detected in various animal species.

Proteomic differentiation pattern in the U937 cell line

The U937 cell line, originally established from a histiocytic lymphoma, has been widely used as a powerful in vitro model for haematological studies. These cells retain the immature cell phenotype and can be induced to differentiate by several factors, among which 12-O-tetradecanoyl-13-phorbol acetate (TPA). Fully differentiated cells acquire the adherent phenotype and exhibit various properties typical of macrophages. However, in spite of a great deal of research devoted to the U937 cellular model, the molecular basis of biological processes involved in the monocyte/macrophage differentiation remains unclear. The present study has been undertaken to contribute to this knowledge, in order to identify proteomic-based differentiation pattern for the U937 cells exposed to TPA. Present results have highlighted that the U937 cell differentiation is correlated with a significant proteomic modulation, corresponding to about 30% of the identified proteins, including both over- and down-regulated proteins. Negative modulation regarded proteins involved in the regulation of cell proliferation and in metabolic processes. Proteins appearing incremented in macrophagic phenotype include calcium- and phospholipid-binding proteins and several proteins related to the phagocytic activity. Conclusively, we suggest that this new set of differentially expressed proteins may represent meaningful myelo-monocytic differentiation markers to be applied to the study of several haematological diseases.