Therapeutic uses of recombinant complement receptors

High-speed single-molecule imaging reveals signal transduction by induced transbilayer raft phases

Using single-molecule imaging with enhanced time resolutions down to 5 ms, we found that CD59 cluster rafts and GM1 cluster rafts were stably induced in the outer leaflet of the plasma membrane (PM), which triggered the activation of Lyn, H-Ras, and ERK and continually recruited Lyn and H-Ras right beneath them in the inner leaflet with dwell lifetimes <0.1 s. The detection was possible due to the enhanced time resolutions employed here. The recruitment depended on the PM cholesterol and saturated alkyl chains of Lyn and H-Ras, whereas it was blocked by the nonraftophilic transmembrane protein moiety and unsaturated alkyl chains linked to the inner-leaflet molecules. Because GM1 cluster rafts recruited Lyn and H-Ras as efficiently as CD59 cluster rafts, and because the protein moieties of Lyn and H-Ras were not required for the recruitment, we conclude that the transbilayer raft phases induced by the outer-leaflet stabilized rafts recruit lipid-anchored signaling molecules by lateral raft-lipid interactions and thus serve as a key signal transduction platform.

Expression of novel Alzheimer's disease risk genes in control and Alzheimer's disease brains

Late onset Alzheimer’s disease (LOAD) etiology is influenced by complex interactions between genetic and environmental risk factors. Large-scale genome wide association studies (GWAS) for LOAD have identified 10 novel risk genes: ABCA7, BIN1, CD2AP, CD33, CLU, CR1, EPHA1, MS4A6A, MS4A6E, and PICALM. We sought to measure the influence of GWAS single nucleotide polymorphisms (SNPs) and gene expression levels on clinical and pathological measures of AD in brain tissue from the parietal lobe of AD cases and age-matched, cognitively normal controls. We found that ABCA7, CD33, and CR1 expression levels were associated with clinical dementia rating (CDR), with higher expression being associated with more advanced cognitive decline. BIN1 expression levels were associated with disease progression, where higher expression was associated with a delayed age at onset. CD33, CLU, and CR1 expression levels were associated with disease status, where elevated expression levels were associated with AD. Additionally, MS4A6A expression levels were associated with Braak tangle and Braak plaque scores, with elevated expression levels being associated with more advanced brain pathology. We failed to detect an association between GWAS SNPs and gene expression levels in our brain series. The minor allele of rs3764650 in ABCA7 is associated with age at onset and disease duration, and the minor allele of rs670139 in MS4A6E was associated with Braak tangle and Braak plaque score. These findings suggest that expression of some GWAS genes, namely ABCA7, BIN1, CD33, CLU, CR1 and the MS4A family, are altered in AD brains.

Anti-tumor immunity and mechanism of immunosuppression mediated by tumor cells: role of tumor-derived soluble factors and cytokines

The immune system plays a crucial role in the protection against tumor growth and progression. However, the activation of the immune system against the neoplastic cells does not always occur and, therefore, tumor cells are able to grow and progress continually in the host. It has now been realized that tumor cells themselves produce many of the important factors that are responsible for dismounting of effective immune response. These tumor-derived soluble factors invariably subdue the functions of almost every immune cell population. Therefore, we attempted to underline the mechanism of anti-tumor immune response and immunosuppression induced by tumor cells.

Early expression changes of complement regulatory proteins and C5A receptor (CD88) on leukocytes after multiple injury in humans

As a crucial element of innate immunity, the complement cascade becomes activated after severe trauma. Regulation of the complement cascade and protection against complement-mediated tissue destruction is provided by a selection of soluble and membrane-bound complement regulatory proteins (CRegs). To date, the leukocyte expression profile of CRegs in multiple injured patients is unknown. In the present study, expression of CRegs and the C5a receptor (CD88) was analyzed on neutrophils, monocytes, and lymphocytes by flow cytometry. Whole blood samples were obtained from healthy volunteers (n = 16) or multiple injured patients (n = 12) on admission in the emergency department and 4, 12, 24, 120, and 240 h after trauma. The content of CRegs and CD88 on leukocytes was significantly altered posttrauma: CD55 (decay accelerating factor) displayed a time-dependent, elevated expression pattern on neutrophils and monocytes, but not on lymphocytes. CD59 (membrane attack complex inhibitor) expression was significantly increased on neutrophils and monocytes at the time of admission and after 5 to 10 days in lymphocytes. CD46 (membrane cofactor protein) was significantly down-regulated in all three cell types posttrauma. CD35 (complement receptor 1) expression on neutrophils was initially decreased, whereas monocytes presented a significant increase in CD35 expression. CD35 on lymphocyte remained unchanged throughout the observation period. CD88 expression was considerably reduced on leukocytes between 0 and 240 h after injury. CD59, CD46, and CD88 expression values on neutrophils reversely correlated with severity of injury. In summary, expression profiles of CRegs and CD88 on leukocytes are specifically altered after polytrauma in humans, indicating a trauma-induced "complementopathy."

Generation of a recombinant, membrane-targeted form of the complement regulator CD59: activity in vitro and in vivo

Inappropriate activation of complement contributes to pathology in diverse inflammatory diseases. Soluble recombinant forms of the natural cell membrane regulators of complement are effective in animal models and some human diseases. However, their use is limited for reasons related to cost, short half lives, and propensity to cause unwanted systemic effects. Some of these limitations may be overcome by use of bacterial expression systems, specific targeting moieties, and judicious choice of regulator. Here we describe the application of these strategies to the generation of a membrane-targeted form of CD59. A recombinant soluble form of rat CD59, comprising the first 71 residues of the mature protein and missing the membrane-anchoring signal, was expressed in bacteria, purified, and refolded in a fully active form. The protein was coupled through its carboxyl terminus to a short, synthetic address tag that confers membrane binding activity. Attachment of the membrane address tag markedly increased complement-inhibitory activity assessed in vitro in hemolysis assays. Intra-articular administration of the tagged agent markedly suppressed disease in a model of rheumatoid arthritis in Lewis rats. This novel type of agent, termed sCD59-APT542, offers for the first time the prospect of efficient and specific inhibition of membrane attack complex activity in vivo.

Administration of a soluble recombinant complement C3 inhibitor protects against renal disease in MRL/lpr mice

Complement receptor 1-related gene/protein y (Crry) in rodents is a potent membrane complement regulator that inhibits complement C3 activation by both classical and alternative pathways. To clarify the role of complement in lupus nephritis, MRL/lpr mice were given Crry as a recombinant protein (Crry-Ig) from 12 to 24 wk of age. Control groups were given saline or normal mouse IgG. Sera and urine were collected biweekly. Only 1 of 20 (5%) Crry-Ig-treated mice developed renal failure (BUN > 50 mg/dl) compared with 18 of 38 (47.4%) mice in control groups (P = 0.001). BUN levels at 24 wk were reduced from 68.8 +/- 9.7 mg/dl in control groups to 38.5 +/- 3.9 mg/dl in the Crry-Ig-treated group (P < 0.01). Urinary albumin excretion at 24 wk was also significantly reduced from 5.3 +/- 1.4 mg/mg creatinine in the control groups to 0.5 +/- 0.2 mg/mg creatinine in the Crry-Ig-treated group (P < 0.05). Of the histologic data at 24 wk, there was a significant reduction in scores for glomerulosclerosis and C3d, IgG, IgG3, and IgA staining intensity in glomeruli in complement-inhibited animals. Crry-Ig-treated animals were also protected from vasculitic lesions. Although there was no effect on relevant autoimmune manifestations such as anti-double stranded DNA titers or cryoglobulin IgG3 levels, circulating immune complex levels were markedly higher in complement-inhibited animals. Thus, inhibition of complement activation with Crry-Ig significantly reduces renal disease in MRL/lpr lupus mice. The data support the strategy of using recombinant complement C3 inhibitors to treat human lupus nephritis.

Use of complement inhibitors in tissue injury

A great deal of information has accumulated implicating the complement system in several human disease processes. Although some of this information is circumstantial, protein inhibitors of the complement system have been developed and applied successfully to experimental disease models in animals. Two inhibitors, soluble complement receptor 1 (sCR1) and anti-C5 monoclonal antibody, are now being investigated in a variety of clinical conditions such as systemic lupus erythematosus and rheumatoid arthritis (RA), diseases for which current therapy has changed little and remains unsatisfactory. Preliminary successes in Phase II clinical trials of RA have provided optimism that complement inhibition might prove useful in these diseases and become part of standard medical therapy.

Regulation of microglia - potential new drug targets in the CNS

Microglia respond to any disturbance in the CNS which poses a threat to physiological homeostasis. Although these responses are secondary, mainly to neuronal alterations, the way the microglial response evolves in many situations promotes further damage to the CNS. The list of clinical conditions in which this situation is a major problem is continuously growing and includes neurodegenerative diseases, stroke, trauma, demyelinating disorders and neuropathic pain. The significance of microglia for the pathogenesis of neurological and neuropsychiatric conditions has led to a rapidly expanding search for therapeutic possibilities to regulate microglial activity. As will be clear from this review, treatments which are currently available appear to offer some positive effects but are still far from satisfactory. A major challenge is to understand the mechanisms that determine whether activated microglia will develop into a cytotoxic or a cytoprotective component.

Targeting of Functional Antibody-Decay-accelerating Factor Fusion Proteins to a Cell Surface

Recombinant soluble complement inhibitors hold promise for the treatment of inflammatory disease and disease states associated with transplantation. Targeting complement inhibitors to the site of complement activation and disease may enhance their efficacy and safety. Data presented show that targeting of decay-accelerating factor (DAF, an inhibitor of complement activation) to a cell surface by means of antibody fragments is feasible and that cell-targeted DAF provides significantly enhanced protection from complement deposition and lysis compared with soluble untargeted DAF. An extracellular region of DAF was joined to an antibody combining site with specificity for the hapten dansyl, at the end of either C(H)1 or C(H)3 Ig regions. The recombinant IgG-DAF chimeric proteins retained antigen specificity and bound to dansylated Chinese hamster ovary cells. Both soluble C(H)1-DAF and C(H)3-DAF were effective at inhibiting complement-mediated lysis of untargeted Chinese hamster ovary cells at molar concentrations within the range reported by others for soluble DAF. However, when targeted to a dansyl-labeled cell membrane, C(H)1-DAF was significantly more potent at inhibiting complement deposition and complement-mediated lysis. Cell-bound C(H)1-DAF also provided cells with protection from complement lysis after removal of unbound C(H)1-DAF. Of further importance, the insertion of a nonfunctional protein domain of DAF (the N-terminal short consensus repeat) between C(H)1 and the functional DAF domain increased activity of the fusion protein. In contrast to C(H)1-DAF, C(H)3-DAF was not significantly better at protecting targeted versus untargeted cells from complement, indicating that a small targeting vehicle is preferable to a large one. We have previously shown that for effective functioning of soluble complement inhibitor CD59, binding of CD59 to the cell surface close to the site of complement activation is required. Significantly, such a constraint did not apply for effective DAF function.

Comparison of the suppressive effects of soluble CR1 and C5a receptor antagonist in acute arthritis induced in rats by blocking of CD59

We investigated the effects of suppression of complement activation at C3 level and inhibition of C5a on acute synovitis in rats. Acute synovitis was induced in Wistar rats by intra-articular (i.a.) injection into one knee of 0.3 mg of MoAb 6D1 (anti-rat CD59 antibody). In the treatment groups, soluble CR1 (sCR1) or C5a receptor (C5aR) antagonist was administered intra-articularly or intravenously and effects on the course of the acute synovitis were monitored. Synovitis induced by 6D1 was characterized by joint swelling, thickening of synovial tissue, cellular infiltration and deposition of membrane attack complex (MAC) on the synovial surface. Neither inflammatory change nor MAC deposition was found in rats which received an i.a. injection of sCR1 to suppress complement activity in the joint. Intra-articular injection of sCR1 did not reduce plasma complement activity. Intravenous administration of sCR1 suppressed plasma complement activity but had no effect on the course of the arthritis and synovitis with MAC deposition was observed. Neither i.a. nor i.v. injection of C5aR antagonist had any suppressive effects on inflammatory change or MAC deposition in synovium. The data show that inflammatory change induced by 6D1 was mediated by local complement activation and was not accompanied by systemic complement activation. C5a generation was not responsible for the observed inflammation, suggesting that other complement activation products, possibly MAC, mediate the inflammatory change observed in this model of acute synovitis in rats.

The role of the complement system in traumatic brain injury

A traumatic impact to the brain induces an intracranial inflammatory response, which consequently leads to the development of brain edema and delayed neuronal death. Evidence from experimental, clinical, and in vitro studies highlight an important role for the complement system in contributing to inflammation within the injured brain. The present review summarizes the current understanding of the mechanisms of complement-mediated secondary brain injury after head trauma.