Complement biosynthesis by mononuclear phagocytes

Intracellular complement activation-An alarm raising mechanism?

It has become increasingly apparent that the complement system, being an ancient defense mechanism, is not operative only in the extracellular milieu but also intracellularly. In addition to the known synthetic machinery in the liver and by macrophages, many other cell types, including lymphocytes, adipocytes and epithelial cells produce selected complement components. Activation of e.g. C3 and C5 inside cells may have multiple effects ranging from direct antimicrobial defense to cell differentiation and possible influence on metabolism. Intracellular activation of C3 and C5 in T cells is involved in the maintenance of immunological tolerance and promotes differentiation of T helper cells into Th1-type cells that activate cell-mediated immune responses. Adipocytes are unique in producing many complement sensor proteins (like C1q) and Factor D (adipsin), the key enzyme in promoting alternative pathway amplification. The effects of complement activation products are mediated by intracellular and cell membrane receptors, like C3aR, C5aR1, C5aR2 and the complement regulator MCP/CD46, often jointly with other receptors like the T cell receptor, Toll-like receptors and those of the inflammasomes. These recent observations link complement activation to cellular metabolic processes, intracellular defense reactions and to diverse adaptive immune responses. The complement components may thus be viewed as intracellular alarm molecules involved in the cellular danger response.

Mammalian DNA is an endogenous danger signal that stimulates local synthesis and release of complement factor B

Complement factor B plays a critical role in ischemic tissue injury and autoimmunity. Factor B is dynamically synthesized and released by cells outside of the liver, but the molecules that trigger local factor B synthesis and release during endogenous tissue injury have not been identified. We determined that factor B is upregulated early after cold ischemia-reperfusion in mice, using a heterotopic heart transplant model. These data suggested upregulation of factor B by damage-associated molecular patterns (DAMPs), but multiple common DAMPs did not induce factor B in RAW264.7 mouse macrophages. However, exogenous DNA induced factor B mRNA and protein expression in RAW cells in vitro, as well as in peritoneal and alveolar macrophages in vivo. To determine the cellular mechanisms involved in DNA-induced factor B upregulation we then investigated the role of multiple known DNA receptors or binding partners. We stimulated peritoneal macrophages from wild-type (WT), toll-like receptor 9 (TLR9)-deficient, receptor for advanced glycation end products (RAGE)⁻/⁻ and myeloid differentiation factor 88 (MyD88)⁻/⁻ mice, or mouse macrophages deficient in high-mobility group box proteins (HMGBs), DNA-dependent activator of interferon-regulatory factors (DAI) or absent in melanoma 2 (AIM2), with DNA in the presence or absence of lipofection reagent. Reverse transcription-polymerase chain reaction, Western blotting and immunocytochemical analysis were employed for analysis. Synthesis of factor B was independent of TLR9, RAGE, DAI and AIM2, but was dependent on HMGBs, MyD88, p38 and NF-κB. Our data therefore show that mammalian DNA is an endogenous molecule that stimulates factor B synthesis and release from macrophages via HMGBs, MyD88, p38 and NF-κB signaling. This activation of the immune system likely contributes to damage following sterile injury such as hemorrhagic shock and ischemia-reperfusion.

Management of hemolytic uremic syndrome

2011 has been a special year for hemolytic uremic syndrome (HUS): on the one hand, the dramatic epidemic of Shiga toxin producing E. coli -associated HUS in Germany brought the disease to the attention of the general population, on the other hand it has been the year when eculizumab, the first complement blocker available for clinical practice, was demonstrated as the potential new standard of care for atypical HUS. Here we review the therapeutic options presently available for the various forms of hemolytic uremic syndrome and show how recent knowledge has changed the therapeutic approach and prognosis of atypical HUS.

Enhancing complement control on endothelial barrier reduces renal post-ischemia dysfunction

BACKGROUND

Excessive complement activation is an integral part of ischemia and reperfusion (IR) injury (IRI) of organs. In kidney transplantation, the pathologic consequence of IRI and complement activation can lead to delayed graft function, which in turn is associated with acute rejection. Previous strategies to reduce complement-induced IRI required systemic administration of agents, which can lead to increased susceptibility to infections/immune diseases. The objective of this study was to determine whether an increase in complement control defenses of rat kidney endothelium reduces IRI. We hypothesized that increased complement control on the endothelial barrier reduces IR-mediated complement activation and reduces kidney dysfunction.

MATERIALS AND METHODS

Fischer 344 rats underwent left kidney ischemia for 45 min and treatment with a novel fusogenic lipid vesicle (FLVs) delivery system to decorate endothelial cells with vaccinia virus complement control protein (VCP), followed by reperfusion for 24 h. Assessment included renal function by serum creatinine and urea, myeloperoxidase assay for neutrophil infiltration, histopathology, and quantification of C3 production in kidneys.

RESULTS

Animals in which the kidney endothelium was bolstered by FLVs+VCP treatment had better renal function with a significant reduction in serum creatinine compared with vehicle controls (P < 0.05). Also, C3 production was significantly reduced (P < 0.05) in treated animals compared with vehicle controls.

CONCLUSION

Increasing complement control at the endothelial barrier with FLVs+VCP modulates complement activation/production during the first 24 h, reducing renal dysfunction following IRI.

Innate immunity in the nervous system

The complement (C) system plays a central role in innate immunity and bridges innate and adaptive immune responses. A fine balance of C activation and regulation mediates the elimination of invading pathogens and the protection of the host from excessive C deposition on healthy tissues. If this delicate balance is disrupted, the C system may cause injury and contribute to the pathogenesis of various diseases, including neurodegenerative disorders and neuropathies. Here we review evidence indicating that C factors and regulators are locally synthesized in the nervous system and we discuss the evidence supporting the protective or detrimental role of C activation in health, injury, and disease of the nerve.

Immune effects of HFO on European sea bass, Dicentrarchus labrax, and Pacific oyster, Crassostrea gigas

The European sea bass, Dicentrarchus labrax, and the Pacific oyster, Crassostrea gigas, were exposed to a soluble fraction of heavy fuel oil for 5 and 9 days, respectively. The organisms were then transferred to non-contaminated seawater for 1 month. The bioaccumulation and elimination of PAHs in contaminated tissues were dissimilar between species. In fish, acenaphthene and naphthalene were detected and naphthalene was still detectable 30 days after the beginning of the recovery period. In oysters, on the other hand, pyrene and phenanthrene were bioaccumulated and 14 days after exposure no more PAHs were detected. Concerning innate immune parameters, the increase of haemolytic activity of the alternative complement pathway in fish and the reduction of phenoloxidase activity in oysters endured, respectively, 1 and 2 weeks in contaminated organisms. This indicates that these two enzymatic cascades could be quite useful for monitoring pollution by oil.

Tactics of Mycobacterium avium subsp. paratuberculosis for intracellular survival in mononuclear phagocytes

Johne's disease is a condition that refers to chronic granulomatous enteritis in ruminants. It is believed that survival and replication of Mycobacterium (M.) paratuberculosis in mononuclear phagocytes plays an important role in the pathogenesis of Johne's disease. However, it is not clear how M. paratuberculosis survives for long time periods in mononuclear phagocytes, nor is it clear which factors trigger multiplication of these bacilli and result in the development of Johne's disease. Investigating the intracellular fate of M. paratuberculosis is challenging because of its very slow growth (more than two months to form visible colonies on media). Existing animal models also have limitations. Despite those obstacles, there has been progress in understanding the intracellular survival tactics of M. paratuberculosis and the host response against them. In this review, we compare known aspects of the intracellular survival tactics of M. paratuberculosis with those of other mycobacterial species, and consider possible mycobactericidal mechanisms of mononuclear phagocytes.

Transcriptional inhibition of interleukin-12 promoter activity in Leishmania spp.-infected macrophages

To establish and persist within a host, Leishmania spp. parasites delay the onset of cell-mediated immunity by suppressing interleukin-12 (IL-12) production from host macrophages. Although it is established that Leishmania spp.-infected macrophages have impaired IL-12 production, the mechanisms that account for this suppression remain to be completely elucidated. Using a luciferase reporter assay assessing IL-12 transcription, we report here that Leishmania major, Leishmania donovani, and Leishmania chagasi inhibit IL-12 transcription in response to interferon-gamma, lipopolysaccharide, and CD40 ligand and that Leishmania spp. lipophosphoglycan, phosphoglycans, and major surface protein are not necessary for inhibition. In addition, all the Leishmania spp. strains and life-cycle stages tested inhibited IL-12 promoter activity. Our data further reveal that autocrine-acting host factors play no role in the inhibitory response and that phagocytosis signaling is necessary for inhibition of IL-12.

The role of complement and Toll-like receptors in organ transplantation

The innate immune system not only participates in host defence but also contributes to the control of adaptive immune responses. Complement and Toll-like receptors (TLR) are key components of innate immunity. Emerging evidence suggests their activation is involved in all major aspects of transplantation. This paper reviews the current understanding of how the complement and TLR on impact transplant injury.

Deficiency of C4 from donor or recipient mouse fails to prevent renal allograft rejection

Complement effector products generated in the transplanted kidney are known to mediate transplant rejection, but which of the three main activation pathways of complement trigger this response is unclear. Here we assessed the role of the classical and lectin pathways by studying the common component C4 in mouse kidney transplant rejection. We transplanted wild-type or C4-null H-2(b) donor kidneys into H-2(k) or H-2(d) recipients, or vice-versa, to assess the roles of donor kidney and recipient expression of complement. Intragraft C4 gene expression rose substantially during rejection. However, we found no significant association between graft acceptance and the presence of C4 in either the donor kidney or recipient mouse. At the time of rejection, we found no significant differences in alloantibody response in the different groups. Tubular deposition of C3 to C9 occurred regardless of the absence or presence of C4 in either the donor or recipient mouse, indicating that C4 was dispensable for complement activation at this site. These data suggest that complement activation and renal allograft rejection are independent of the classical and lectin pathways in these models, implying that in the absence of these pathways the alternative pathway is the main trigger for complement-mediated rejection.

Macrophages from C3-deficient mice have impaired potency to stimulate alloreactive T cells

Impaired T-cell reactivity is a feature of C3-deficient mice in several disease models. The mechanism behind the reduced T-cell response is, however, poorly understood. We explored the hypothesis that antigen-presenting cells (APCs) from C3-/- mice have impaired potency to stimulate antigen-specific T cells, in an alloantigen-dependent model. Our results show that C3-/- macrophages have reduced ability to elicit alloreactive T-cell responses in vitro and in vivo, affecting both the primary and secondary responses. The C3 status of donor macrophages had a major impact on the CD4 T-cell response. The impaired CD4 T-cell response was associated with reduced expression of MHC class II on the surface of C3-/- macrophages, without loss of class II gene expression. Furthermore, inhibition of C3 gene expression in C3+/+ macrophages reduced their ability to stimulate alloreactive T cells, suggesting that endogenous production of C3 could in part contribute to the potency of APCs. Our data provide compelling evidence that C3 deficiency modulates the potency of APCs to stimulate the T-cell response, suggesting a critical role for complement in the maintenance of APC function. This could offer a partial explanation as to why the T-cell response is impaired in C3-/- mice. (Blood. 2006;107:2461-2469)

Local extravascular pool of C3 is a determinant of postischemic acute renal failure

The third complement component (C3) is an acute phase protein that plays a central role in reperfusion injury in several organ models. To investigate the contribution of local synthesis of C3 and distinguish it from that of circulating complement mainly produced by hepatic synthesis, we employed a mouse renal isograft model. Our model demonstrated a close relationship between the extent of intrarenal expression of C3 and cold-ischemia induced injury. Ischemic C3-positive donor kidneys transplanted into C3-positive or C3-negative recipients developed widespread tissue damage and severe acute renal failure. In contrast, ischemic C3-negative isografts exhibited only mild degrees of functional and structural disturbance, even when transplanted into normal C3-positive recipients. Thus local synthesis of C3, mostly identified in the tubular epithelium, was essential for complement-mediated reperfusion damage, whereas circulating C3 had a negligible effect. Our results suggest a two-compartment model for the pathogenic function of C3, in which the extravascular compartment is the domain of local synthesis of C3, and where the role of circulating C3 is redundant. Our data cast new light on the mechanism of complement-mediated tissue injury in nonimmunological disorders, and challenges the longstanding dogma that circulating components are the main complement effectors of extravascular tissue damage.

Allograft rejection: effect of local synthesis of complement

The complement system is known for its ability to participate in non-specific inflammation and membrane injury as well as contributing to antigen-specific immune stimulation. In renal transplantation, the complement cascade behaves true to form in that both non-immune- and immune-mediated destruction of the renal tubules are complement dependent. What is remarkable, however, is the extent of involvement of local synthesis of complement in both of these injuries, suggesting that the extravascular tissue compartment is the domain of local synthesis, whereas the effect of circulating complement is much less. This creates a new paradigm for studying the influence of local synthesis of complement in other organ-based diseases and underlines the need for tissue-targeting strategies in successful therapeutic development.

The biology of human lymphoid malignancies revealed by gene expression profiling

Gene expression profiling provides a quantitative molecular framework for the study of human lymphomas. This genomic technology has revealed that existing diagnostic categories are comprised of multiple molecularly and clinically distinct diseases. Diffuse large B-cell lymphoma (DLBCL), for example, consists of three gene expression subgroups, termed germinal center B-cell-like (GCB) DLBCL, activated B-cell-like (ABC) DLBCL, and primary mediastinal B-cell lymphoma (PMBL). These DLBCL subgroups arise from different stages of normal B-cell differentiation, utilize distinct oncogenic mechanisms, and differ in their ability to be cured by chemotherapy. Key regulatory factors and their target genes are differentially expressed among these subgroups, including BCL-6, Blimp-1, and XBP1. ABC DLBCL and PMBL depend upon constitutive activation of the NF-kappaB pathway for their survival but GCB DLBCL does not, demonstrating that this pathway is a potential therapeutic target for certain DLBCL subgroups. In DLBCL, mantle cell lymphoma, and follicular lymphoma, gene expression profiling has also been used to create gene expression-based models of survival, which have identified the biological characteristics of the tumors that influence their clinical behavior. In mantle cell lymphoma, the length of survival following diagnosis is primarily influenced by the tumor proliferation rate, which can be quantitatively measured by a proliferation gene expression "signature." Based on this accurate measure, the proliferation rate can now be viewed as an integration of several oncogenic lesions that each increase progression from the G1 to the S phase of the cell cycle. In DLBCL and follicular lymphoma, gene expression profiling has revealed that the molecular characteristics of non-malignant tumor-infiltrating immune cells have a major influence on the length of survival. The implications of these insights for the diagnosis and treatment of non-Hodgkin lymphomas are discussed.

Z39Ig is co-expressed with activated macrophage genes

Z39Ig is a recently-identified gene with immunoglobulin-like domains whose function is unknown. We examined expression of Z39Ig in 1432 human cDNA libraries, and found it primarily in synovium of patients with rheumatoid arthritis, in placenta, and in lung. We analyzed its co-expression pattern using the Guilt-by-Association (GBA) algorithm, and found that it is most similar in expression to early genes in the classical complement system (C1qA, C1qB, C1qC, C1r, and C1 inhibitor), MHC class II genes (HLA-DR alpha, HLA-DR beta 1, and HLA-DP alpha 1), Fc receptors (Fc gamma RIIa and Fc epsilon R1), lysosomal protein (LAPTm5), tissue transglutaminase, and macrophage receptors (MARCO and CD163/M130). The sequence and expression data suggest that Z39Ig is a cell surface receptor, expressed in activated macrophages, and linked with the classical complement system, most likely in phagocytosis preceding antigen presentation. Knowledge of this gene may contribute to better understanding of the role of complement and activated macrophages in rheumatoid arthritis and systemic lupus.

Pathogenesis and immune response in Atlantic salmon (Salmo salar L.) parr experimentally infected with salmon pancreas disease virus (SPDV)

Atlantic salmon parr were injected intraperitoneally with salmon pancreas disease virus (SPDV) grown on CHSE-214 cells. The viraemia, the histopathological changes in target organs and some immune parameters were taken at intervals up to 30 days post-infection (dpi). The earliest kind of lesion was necrosis of exocrine pancreas, appearing as soon as 2 dpi. It progressed towards complete tissue breakdown at 9 dpi before resolving gradually. Concurrent to this necrosis, a strong inflammatory response was in evidence from 9 dpi in the pancreatic area for a majority of fish. A necrosis of the myocardial cells of the ventricle occurred in infected fish mainly at 16 dpi and it faded thereafter. The monitoring of the plasma viral load showed a rapid haematogenous spreading of SPDV, peaking at 4 dpi, but also the absence of a secondary viraemia. No interferon (IFN) was detected following the infection of parr with SPDV, probably owing to an IFN activity in Atlantic salmon below the detection level of the technique. Neutralising antibodies against SPDV were in evidence from 16 dpi and they showed a time-related increasing titre and prevalence. The phagocytic activity in head-kidney leucocytes was always significantly higher in the infected fish than in the control fish, being particularly high by 9 dpi. Lysozyme and complement levels were both increased and they peaked significantly in the infected fish at 9 and 16 dpi respectively. These results demonstrated that an experimental infection of Atlantic salmon parr with SPDV provoked a stimulation of both specific and non-specific immunity with regards to the viraemia and the histopathology.

Pulmonary surfactant in innate immunity and the pathogenesis of tuberculosis

Components of the innate immune system serve to protect the host from invading pathogens prior to the generation of a directed immune response, and influence the manner in which the directed immune response develops. The pulmonary surfactant system consists of a complex array of proteins and lipids that reduce surface tension of the alveoli, and appears to play an essential role in innate immunity. Investigators have recently gained insight into the interactions between components of the surfactant system and the respiratory pathogen Mycobacterium tuberculosis. It is likely that pulmonary surfactant and other innate immune determinants play significant roles in the pathogenesis of tuberculosis.

C6 produced by macrophages contributes to cardiac allograft rejection

The terminal components of complement C5b-C9 can cause significant injury to cardiac allografts. Using C6-deficient rats, we have found that the rejection of major histocompatibility (MHC) class I-incompatible PVG.R8 (RT1.A(a)B(u)) cardiac allografts by PVG.1U (RT1.A(u)B(u)) recipients is particularly dependent on C6. This model was selected to determine whether tissue injury results from C6 produced by macrophages, which are a conspicuous component of infiltrates in rejecting transplants. We demonstrated that high levels of C6 mRNA are expressed in isolated populations of macrophages. The relevance of macrophage-produced C6 to cardiac allograft injury was investigated by transplanting hearts from PVG. R8 (C6-) donors to PVG.1U (C6-) rats which had been reconstituted with bone marrow from PVG.1U (C6+) rats as the sole source of C6. Hearts grafted to hosts after C6 reconstitution by bone marrow transplantation underwent rejection characterized by deposition of IgG and complement on the vascular endothelium together with extensive intravascular aggregates of P-selectin-positive platelets. At the time of acute rejection, the cardiac allografts contained extensive perivascular and interstitial macrophage infiltrates. RT-PCR and in situ hybridization demonstrated high levels of C6 mRNA in the macrophage-laden transplants. C6 protein levels were also increased in the circulation during rejection. To determine the relative contribution to cardiac allograft rejection of the low levels of circulating C6 produced systemically by macrophages, C6 containing serum was passively transferred to PVG.1U (C6-) recipients of PVG.R8 (C6-) hearts. This reconstituted the C6 levels to about 3 to 6% of normal values, but failed to induce allograft rejection. In control PVG.1U (C6-) recipients that were reconstituted with bone marrow from PVG.1U (C6-) donors, C6 levels remained undetectable and PVG.R8 cardiac allografts were not rejected. These results indicate that C6 produced by macrophages can cause significant tissue damage.

Complement activation and CD59 expression in the motor facial nucleus following intracranial transection of the facial nerve in the adult rat

Intracranial transection of the facial nerve has been shown to cause a massive neuronal cell death in the motor facial nucleus. Complement activation has been proposed to contribute to neuronal degeneration following axotomy. Using immunocytochemistry and in situ hybridization we show in the present study that there is complement activation in the facial nucleus after intracranial facial nerve transection as well as increase of the complement regulators CD59 and clusterin. We propose a neuroprotective role for the complement regulators CD59 and clusterin against homologous attack of complement to facial motor neurons.

Soluble complement receptor 1 (sCR1) is not as effective as cobra venom factor in the treatment of experimental allergic neuritis

To further investigate the role of complement activation in Experimental Allergic Neuritis (EAN), the effect of systemic complement blockade by soluble CR1 (sCR1) was compared to complement depletion by Cobra Venom Factor (CVF) in EAN rats immunized with bovine peripheral nerve myelin. EAN rats treated with CVF (n = 10) had significantly reduced clinical scores compared to rats treated with sCR1 (n = 9) or saline (n = 10) (score: sCR1 0.66 +/- 0.7; CVF 0; saline 0.6 +/- 0.8; mean +/- SD). CVF treatment more effectively decreased inflammation and demyelination compared to sCR1 treatment which had only a partial effect (inflammation: sCR1 1.8 +/- 1.4; CVF 0.3 +/- 0.7; saline 1.9 +/- 1.2; demyelination; sCR1 1.3 +/- 1; CVF 0.1 +/- 0.6; saline 1.7 +/- 1.2). In lumbosacral nerve roots significantly less infiltrating ED1 positive macrophages and CD11bc (expressing complement receptor 3 or CR3) positive inflammatory cells were present in CVF treated EAN rats while there was a limited decrease in inflammation in the sCR1 treated animals compared to the saline treated rats (ED1: sCR1 1.4 +/- 1.2; CVF 0.5 +/- 0.6; saline 1.7 +/- 1.2; CD11bc: sCR1 1.9 +/- 1.2; CVF 0.9 +/- 1; saline 2.1 +/- 1.2). Our findings suggest that complement depletion by CVF is more effective than complement blockade by sCR1 in reducing the severity of inflammatory peripheral nerve demyelination.

Complement and clusterin in the injured nervous system

Peripheral nerve injury and neuronal degeneration resulting from toxic ricin induce activation of the classical pathway of complement close to the injured motorneuron perikarya or sensory terminals. In contrast, degeneration of central myelinated fibers is not accompanied by complement expression. The main source of complement in peripheral nerve injury and toxic ricin degeneration appears to be microglia. Brain contusion is associated with complement activation. Some of the complement in this situation may derive from plasma, because the blood-brain barrier is disrupted. Clusterin expression is increased in astrocytes along with their activation in the vicinity of lesioned neurons. In addition, axotomized motorneurons show a marked clusterin upregulation. A relationship between clusterin and cell death is suggested by the prominent aggregation of clusterin in neuronal perikarya destroyed by the effects of toxic ricin, as well as by the neosynthesis of clusterin in apparently degenerating nonneuronal cells, presumed to be oligodendrocytes. Our findings indicate that the expression of complement and clusterin are prominent features of neural degeneration and regeneration, as it is in Alzheimer's disease brains as well. The nerve injury conditions described, therefore, offer attractive experimental models to elucidate the roles of these molecular components in neurodegenerative disorders, thereby providing useful insights into potentially new therapeutic approaches in these conditions.

Interleukin-1 alpha, interleukin 6 and tumor necrosis factor alpha increase the synthesis and expression of the functional alternative and terminal complement pathways by human umbilical vein endothelial cells in vitro

The proinflammatory cytokines interleukin 1 alpha (IL-1 alpha), tumor necrosis factor alpha (TNF alpha) and interleukin 6 (IL-6) modulate the synthesis of complement factors B and C3 by endothelial cells (EC), and are considered to play an important role in the development of sepsis. By using agarose beads activating the alternative pathway of complement, we wanted to study the net effect of these cytokines on EC synthesis of the alternative and terminal pathways, measured by binding of anti-C3c and anti-TCC (terminal complement complex) antibodies to beads kept with the EC. Addition of IL-1 alpha and TNF alpha at concentrations of 50 and 100 U/ml resulted in a significant increase in binding of these antibodies to co-incubated beads, most pronounced for anti-C3c. IL-6 from 50-200 U/ml resulted in a stronger (two to fourfold) binding for both antibodies compared to experiments with IL-1 alpha and TNF. However, increased concentrations of IL-1 alpha (200 U/ml) and IL-6 (400 U/ml) resulted in a strong reduction in binding of anti-C3c and anti-TCC antibodies to the co-cultured beads. This study indicates that proinflammatory cytokines upregulate the synthesis by EC of the functional alternative and terminal pathways of complement.

Complement depletion affects demyelination and inflammation in experimental allergic neuritis

The effect of systemic complement depletion by cobra venom factor (CVF) on experimental allergic neuritis (EAN) was studied in rats immunized with variable amounts of bovine peripheral nerve myelin. Low-dose myelin EAN rats treated with CVF i.p. (n = 10) had lower clinical scores (0.3 +/- 0.7 vs. 1.1 +/- 1.1), less demyelination (0.4 +/- 0.8 vs. 1.9 +/- 1.1) and inflammation (0.6 +/- 1.2 vs. 2 +/- 1) than EAN animals treated with i.p. saline (n = 10). Endoneurial infiltrates had fewer ED1-positive (phagocytic) macrophages (0.4 +/- 0.5 vs. 1.6 +/- 1.1) and CD11bc-positive (expressing iC3b receptor or CR3) cells (1 +/- 0.8 vs. 2.5 +/- 0.8) (mean +/- S.D.) detected by immunocytochemistry. This effect was partially abrogated by immunizing animals with a higher dose of myelin. Our studies suggest that complement may play a role in the recruitment of macrophages into the endoneurium and in opsonizing myelin for phagocytosis.

Physiology and pathophysiology of complement: progress and trends

The complement system comprises a family of at least 20 plasma and membrane proteins that interact in a tightly regulated cascade system to destroy invading bacteria and prevent the deposition of immune complexes in the tissues. This brief review addresses the basic mechanisms of complement activation and control and describes the active fragments produced during complement activation. The biological importance of the complement system is amply illustrated in patients with complement deficiencies, who are susceptible to bacterial infections and immune complex diseases. The involvement of complement in other immunological diseases is an expanding area of clinical research, supported by the development of new assays for the identification of complement activation. This area is discussed here with particular reference to neurological diseases. A promising new prospect involves the use of complement inhibitory molecules in therapy of complement-mediated disease and this exciting area is also discussed. Novel physiological roles of complement also are being revealed and new evidence that complement and complement receptors play an important role in reproduction is summarized. It is hoped that this brief overview will convey some of the enthusiasm currently pervading research in this underappreciated area of immunology.