Mini-review: A pivotal role for innate immunity in the clearance of apoptotic cells

Apoptotic cells can be recognized and taken up by both macrophages and dendritic cells. Phagocytosis of apoptotic cells generally leads to active suppression of cytokine production by professional phagocytes. This is different from the response towards cells that die by necrosis, which induce a pro-inflammatory cytokine profile. Uptake of apoptotic cells involves a large number of receptors and opsonins, which bind to cellular ligands exposed during the various stages of apoptotic cell death. Among the opsonins of apoptotic cells, complement factors, including C1q, and complement-activating members of the pentraxin family play an important role. This is indicated by in vitro phagocytosis studies and supported by the susceptibility to systemic autoimmunity of carriers of genetic deficiencies for early complement proteins. The present review summarizes the role of molecules of innate immunity in the handling of apoptotic cells by macrophages and dendritic cells. It is proposed that C1q and other opsonins prevent autoimmunity and maintain self-tolerance by supporting the efficient clearance of apoptotic material, as well as by actively modulating phagocyte function.     

Complexes between C1q and C3 or C4: novel and specific markers for classical complement pathway activation

Classical pathway activation is often assessed by measuring circulating levels of activated C4. However, this parameter does not discriminate between activation through the classical or the lectin pathway. We hypothesized that during classical pathway activation, complexes are formed between C1q and activated C4 or C3. Using ELISA, we investigated whether such complexes constitute specific markers for classical pathway activation. In vitro, C1q-C3d/C4d complexes were generated upon incubation of normal recalcified plasma with aggregated IgG or an anti-C1q mAb that activates C1 (mAb anti-C1q-130). In contrast, during incubation with C1s or trypsin, C1q-C3d/C4d complexes were not generated, which excludes an innocent bystander effect. Additionally, C1q-C3d/C4d complexes were not generated during activation of the alternative or the lectin pathway. Repeated freezing and thawing did not influence levels of C1q-C3d/C4d complexes in recalcified plasma. To measure C1q-complement complexes in plasma samples, we separated unbound complement proteins from C1q-C3d/C4d complexes in the samples prior to testing with ELISA. In samples from patients undergoing cardiopulmonary bypass surgery or suffering from rheumatoid arthritis, we found higher levels of C1q-C4 complexes than in samples from healthy individuals. We conclude that complexes between C1q and C4 or C3 are specific markers of classical complement pathway activation.     

Controlled stomach fistula for acute operated ulcer. Case report

The authors analyze the case of a 65 old woman which was hospitalized for sigmoidian stenosant and haemorrhagical neoplasm, confined to the colic wall, without peritoneal or hepatic metastases, and without peritoneal or parietal invasion. Surgical management included sigmoidectomy and termino-terminal anastomosis for reconstructing intestinal transit followed by peritoneal drainage. In early postoperative stage the aspect of generalized peritonitis occurs and there is suspicion of anastomotic fistulae. On surgery, acute and perforated gastric ulcer is found, located in close vicinity to the cardia, on the anterior side of the stomach. Suture of the perforation is undertaken with drainage of the peritoneal cavity, but successfully because fistulization of the sutured perforation followed. Under the given circumstances controlled drainage of the gastric fistulae was carried out, using a Folley probe extended through the fistulae orifice and through the anterior abdominal wall, lateral to the median incision. The blowing of the intragastric balloon and the setting into tension of the gastric wall to the front abdominal wall allowed the sealing of the fistulae route but it took about three months. This technical contrivance has afforded good postoperative evolution and recovery of the patient, who after five years from surgery is in a good condition and has no subjective complaints.     

Congenital heart disease: gated MR imaging in 72 patients

Seventy-two patients (aged 2 months to 75 years; mean 23 years) with a variety of congenital anomalies of the heart and great vessels underwent ECG-gated magnetic resonance (MR) imaging using the multisectional spin-echo technique (0.35 Tesla). The ability to define segmental anatomy and intracardiac anomalies on transverse, sagittal, and coronal images was evaluated. MR images were graded as excellent, diagnostic, or nondiagnostic, and MR findings were corroborated by angiography and/or two-dimensional echocardiography. Studies that were considered to be excellent or diagnostic were obtained in 96% of the cases. Visceroatrial situs, the type of ventricular loop, and the relationship of the great vessels could be identified in all patients with studies encompassing the entire heart. Forty-four of 47 abnormalities at the level of the great vessels were identified with MR, including coarctation of the aorta and vascular rings. MR showed 32 of 35 ventricular abnormalities; 2 small ventricular septal defects and 1 Ebstein anomaly were not demonstrated. All of the abnormalities at the atrial level and those of systemic and pulmonary venous return were seen on MR images. Complex cardiac anomalies, such as single ventricles, and the status of the pulmonary arteries were clearly demonstrated, and a good assessment of total and palliative postoperative anatomy was provided.     

Effect of monomeric immunoglobulin G (IgG) on the clearance of soluble aggregates of IgG in man.

Serum concentrations of IgG may influence Fc receptor-mediated clearance of immune complexes. For instance, when 123I-labeled aggregates of human IgG (123I-AIgG), used as a model for soluble immune complexes, are administered to patients with systemic lupus erythematosus (SLE), there is an inverse correlation between the serum concentrations of IgG and the clearance and volume of distribution in steady state (Vss) of 123I-AIgG. To answer the question whether IgG has a direct effect on the clearance of immune complexes, we measured the elimination of 123I-AIgG in eight patients with hypogammaglobulinemia, before and after substitution with intravenous gammaglobulin (IVIG). As expected, raising IgG concentrations in these patients (by 6 g/l) caused a significant decrease of the Vss of 123I-AIgG. However, clearance of 123I-AIgG remained unchanged by IVIG. Thus, the results of this study offer no experimental evidence that raising concentrations of IgG influences the clearance of soluble immune complexes.     

Complement and renal disease

The complement system is involved in several aspects of renal disease, including primary renal diseases, dialysis and renal transplant rejection. Initially, a role for complement in renal disease was inferred solely from the deposition of complement components in affected kidneys and changes in complement levels in the circulation during active disease. Recent studies have shown how complement modulates the onset, development and the resolution of renal disease. Current research provides clues on the role of individual complement components and activation pathways as well as possible modes of complement regulation in the management of renal disease.     

Cytokines affect resistance of human renal tumour cells to complement-mediated injury

Overexpression of membrane-bound complement regulatory proteins (mCRPs) on tumour cells may hamper the effect of immunotherapy with complement-activating monoclonal antibody (MoAb). Therefore, it is important to investigate whether cytokines can downregulate the expression of mCRP on tumour cells. In this study, the effect of 10 cytokines on the expression of the mCRP CD46, CD55 and CD59 and the renal tumour-associated antigen G250/MN/CAIX on four human renal tumour cell lines and proximal tubular epithelial cells was determined by flow cytometry. In addition, it was measured whether changes in the expression of the classical pathway regulatory proteins CD55 and CD59 had an effect on C3 deposition and lysis. Interleukin-1beta (IL-1beta) consistently downregulated the expression of CD46 and CD59; IL-4 consistently downregulated the expression of CD46 and transforming growth factor-beta1, consistently downregulated the expression of both CD46 and CD55. However, treatment with IL-1beta and IL-4 also decreased the expression of G250/MN/CAIX. Changes in the expression of CD55 and CD59 were associated with changes in the amount of C3 deposited and the extent of complement-mediated lysis, respectively. This suggests that clinical immunotherapy, consisting of treatment with cytokines and MoAb, may induce either up- or downregulation of CD55 or CD59 and thus affect the effectiveness of immunotherapy with MoAb.     

Connective tissue growth factor and igf-I are produced by human renal fibroblasts and cooperate in the induction of collagen production by high glucose

Tubulointerstitial fibrosis is an important component in the development of diabetic nephropathy. Various renal cell types, including fibroblasts, contribute to the excessive matrix deposition in the kidney. Although transforming growth factor-beta (TGF-beta) has been thought to play a major role during fibrosis, other growth factors are also involved. Here we examined the effects of connective tissue growth factor (CTGF) and IGF-I on collagen type I and III production by human renal fibroblasts and their involvement in glucose-induced matrix accumulation. We have demonstrated that both CTGF and IGF-I expressions were increased in renal fibroblasts under hyperglycemic conditions, also in the absence of TGF-beta signaling. Although CTGF alone had no effect on collagen secretion, combined stimulation with IGF-I enhanced collagen accumulation. Furthermore, IGF-I also had a synergistic effect with glucose on the induction of collagens. Moreover, we observed a partial inhibition in glucose-induced collagen secretion with neutralizing anti-CTGF antibodies, thereby demonstrating for the first time the involvement of endogenous CTGF in glucose-induced effects in human renal fibroblasts. Therefore, the cooperation between CTGF and IGF-I might be involved in glucose-induced matrix accumulation in tubulointerstitial fibrosis and might contribute to the pathogenesis of diabetic nephropathy.