Anna Erdei

C3a and C3b Activation Products of the Third Component of Complement (C3) Are Critical for Normal Liver Recovery after Toxic Injury

Although the complement system has been implicated in liver regeneration after toxic injury and partial hepatectomy, the mechanism or mechanisms through which it participates in these processes remains ill-defined. In this study, we demonstrate that complement activation products (C3a, C3b/iC3b) are generated in the serum of experimental mice after CCl4 injection and that complement activation is required for normal liver regeneration. Decomplementation by cobra venom factor resulted in impaired entry of hepatocytes into S phase of the cell cycle. In addition, livers from C3-deficient (C3−/−) mice showed similarly impaired proliferation of hepatocytes, along with delayed kinetics of both hepatocyte hyperplasia and removal of injured liver parenchyma. Restoration of hepatocyte proliferative capabilities of C3−/− mice through C3a reconstitution, as well as the impaired regeneration of C3a receptor-deficient mice, demonstrated that C3a promotes liver cell proliferation via the C3a receptor. These findings, together with data showing two waves of complement activation, indicate that C3 activation is a pivotal mechanism for liver regeneration after CCl4 injury, which fulfills multiple roles; C3a generated early after toxin injection is relevant during the priming of hepatocytes, whereas C3 activation at later times after CCl4 treatment contributes to the clearance of injured tissue.

The role of C3 in the immune response

The complement system, particularly the third component, plays an important modulatory role in the inductive phase of the immune response. As discussed here by Anna Erdei and colleagues, the picture that is emerging is that immobilized C3 split products facilitate the cooperation between immunocompetent cells and are co-stimulatory molecules in T- and B-cell activation, probably as a result of their ability to promote cell-cell adhesion. In contrast, soluble C3 products inhibit lymphocyte proliferation.

Natively unfolded tubulin polymerization promoting protein TPPP/p25 is a common marker of alpha-synucleinopathies

The novel basic, heat-stable tubulin polymerization promoting protein TPPP/p25 is associated with microtubules in vitro and can induce the formation of aberrant microtubule assemblies. We show by 1H-NMR spectroscopy that TPPP/p25 is natively unfolded. Antisera against peptide 186GKGKAGRVDLVDESG200NH2 (186-200) are highly specific to TPPP/p25. Immunohistochemistry and confocal microscopy demonstrates that TPPP/p25 is enriched in filamentous alpha-synuclein bearing Lewy bodies of Parkinsons (PD) and diffuse Lewy body disease (DLBD), as well as glial inclusions of multiple system atrophy (MSA). There is a correlation between TPPP/p25 and alpha-synuclein immunoreactivity in Western blot. In contrast, TPPP/p25 is not associated with abnormally phosphorylated tau in various inclusions of Picks disease (PiD), progressive supranuclear palsy (PSP), and corticobasal degeneration (CBD). However, electron microscopy confirms clusters of TPPP/p25 immunoreactivity along filaments of unstructured but not compact neurofibrillary tangles in Alzheimers disease (AD). TPPP/p25 seems to be a novel marker of alpha-synucleinopathies.

Cutting Edge: Productive HIV-1 Infection of Dendritic Cells via Complement Receptor Type 3 (CR3, CD11b/CD18)

In the present study, we demonstrate that macrophage-tropic HIV-1 opsonized by complement and limited amounts of anti-HIV-IgG causes up to 10-fold higher productive infection of human monocyte-derived dendritic cells than HIV treated with medium or HIV opsonized by Ab only. Enhanced infection is completely abolished by a mAb specific for the ligand-binding site of CD11b (i.e., α-chain of complement receptor 3, receptor for iC3b), proving the importance of complement receptor 3 in this process. Inhibition of complement activation by EDTA also prevents enhanced infection, further demonstrating the role of complement in virus uptake and productive infection. Since HIV is, even in the absence of Abs, regularly opsonized by complement, most probably the above-described mechanism plays a role during in vivo primary infection.

Complement Receptor Type 1 (CD35) Mediates Inhibitory Signals in Human B Lymphocytes

The complement system—particularly component C3—has been demonstrated to be a key link between innate and adaptive immunity. The trimolecular complex of complement receptor type 2 (CR2), CD19, and CD81 is known to promote B cell activation when coligated with the B cell Ag receptor. In the present study, we aimed to elucidate the role of human complement receptor type 1 (CR1), the other C3-receptor on B cells. As ligand, aggregated C3 and aggregated C3(H2O), i.e., multimeric “C3b-like C3”, are used, which bind to CR1, but not to CR2. In experiments studying the functional consequences of CR1-clustering, the multimeric ligand is shown to inhibit the proliferation of tonsil B cells activated with a suboptimal dose of anti-IgM F(ab′)2. Importantly, this inhibitory activity also occurs in the presence of the costimulatory cytokines IL-2 and IL-15. The anti-IgM-induced transient increase in the concentration of intracellular free Ca2+ and phosphorylation of several cytoplasmic proteins are strongly reduced in the presence of the CR1 ligand. Data presented indicate that CR1 has a negative regulatory role in the B cell Ag receptor mediated activation of human B lymphocytes.

The brain-specific protein TPPP/p25 in pathological protein deposits of neurodegenerative diseases

Immunohistochemical detection of protein components of pathological inclusions is widely used for neuropathological diagnosis of neurodegenerative disorders. However, different antibodies and antigen unmasking methods may account for variability between research studies and thus may affect diagnostic accuracy. Using two different antibodies raised against either a segment (184–200 aa) or the full length of human recombinant brain-specific tubulin polymerization promoting protein TPPP/p25, we immunohistochemically screened neurodegenerative disorders, both with and without pathological α-synuclein structures. We tested three different epitope unmasking methods, we applied laser confocal microscopy to evaluate double immunolabelling, and we compared the amount of structures exhibiting TPPP/p25 and α-synuclein immunoreactivity. We demonstrate that there are a variety of staining patterns depending on the epitope retrieval method and antibody used. The antibody raised against aa 184–200 segment of TPPP/p25 is better in immunolabelling the majority of α-synuclein immunopositive neuronal and glial pathological profiles detectable in Parkinson’s disease, diffuse Lewy-body disease, and multiple system atrophy, in addition to immunostaining some extracellular huntingtin immunoreactive structures, lipofuscin, and neuromelanin particles. In contrast, the one raised against the full-length human recombinant TPPP/p25 is more suitable to immunodetect normal oligodendrocytes. Exposition of the segment aa 184–200 of TPPP/p25 in the aggregates of pathological inclusions renders this antibody a reliable marker of all types of α-synucleinopathies and suggests a role for TPPP/p25 in the aggregation process of some neurodegenerative conditions.

Cross-Linking of CD32 Induces Maturation of Human Monocyte-Derived Dendritic Cells Via NF-κB Signaling Pathway

Dendritic cells (DC) represent a unique set of APCs that initiate immune responses through priming of naive T cells. Maturation of DC is a crucial step during Ag presentation and can be induced by triggering a broad spectrum of DC surface receptors. Although human DC express several receptors for the Fc portion of IgG which were described to play an important role in Ag internalization, little is known about the effects of IgG or immune complexes on DC maturation. In this study, we show that cross-linking of FcγR-type II (CD32) with immobilized IgG (imIgG) can induce maturation of human monocyte-derived DC via the NF-κB signaling pathway. IgG-mediated maturation was accompanied by a moderate increase of IL-10 secretion, whereas no IL-12 production was observed. Involvement of CD32 was further supported by experiments with the anti-CD32 mAb, which blocked IgG-triggered DC maturation and cytokine secretion significantly. Furthermore, DC cultivated in the presence of imIgG induced allogeneic T cell proliferation. Because this imIgG-induced maturation was considerably impaired in monocyte-derived DC from systemic lupus erythematosus patients, we suggest that DC, which matured in the presence of immune complexes, may contribute to prevention of pathological immune responses.

C5a and C5a(desArg) enhance the susceptibility of monocyte-derived macrophages to HIV infection.

Mononuclear phagocytes, which include circulating blood monocytes and differentiated tissue macrophages, are believed to play a central role in the sexual transmission of HIV infection. The ability of HIV to productively infect these cells may be influenced by action of exogenous or host-derived substances at the site of viral entry. Given the potent capacities of inflammatory mediators to stimulate anaphylatoxic and immunomodulatory functions in mucosa, the effects of complement-derived anaphylatoxins on the susceptibility of monocytes and monocyte-derived macrophages (MDM) to HIV-1 infection were examined. In our in vitro system, the susceptibility to infection was up to 40 times increased in MDM that had been exposed to C5a or C5adesArg, but not to C3a or C3adesArg, for 2 days before adding of virus. By contrast, the treatment with complement anaphylatoxins did not affect HIV replication in fresh monocytes. Stimulatory effect of C5a and its desArg derivative on HIV infection correlated with the increase of TNF-α and IL-6 secretion from MDM. All these functional effects of C5a and C5adesArg were reversible by treatment of cells with the mAb that functionally blocks C5aR. Taken together, these results indicate that C5a and C5adesArg may increase the susceptibility of MDM to HIV infection through stimulation of TNF-α and IL-6 secretion from these cells.

Complement research: biosynthesis, genetics, immunoregulatory role and clinical studies

Complementology is one of the major areas of immunological research in Hungary. Here, András Falus and colleagues describe studies on the control of biosynthesis of complement components and on the nature and function of receptors in the complement system.

Expression and role of CR1 and CR2 on B and T lymphocytes under physiological and autoimmune conditions

The involvement of complement in the development and regulation of antibody responses under both healthy and pathological conditions is known for long. Unravelling the molecular mechanisms underlying the events however is still in progress. This review focuses on the role of complement receptors CR1 (CD35) and CR2 (CD21) expressed on T and B cells. Alteration in the expression and function of these receptors may contribute to the initiation and maintenance of immune complex mediated autoimmune diseases such as systemic lupus erythematosus and rheumatoid arthritis. Recent data regarding complement receptor expression on T lymphocytes and on memory B cells are also discussed.