Kinetic studies of neutrophil phagocytosis: V. Studies on the co-operation between the Fc and C3b receptors

The co-operation between the Fc and C3b receptors of PMNs (neutrophil granulocytes) during phagocytosis has been studied by the effect of interference with either of the receptors. The significance of the Fc receptor for the mediation of internalization proposed by previous investigators was confirmed by the inhibition of both Fc- and C3b-mediated phagocytosis by Fc fragments of IgG and by Fab fragments of antiserum against the Fc part of IgG. C3b-receptor-mediated phagocytosis was inhibited by trypsin, granulocyte elastase, myeloperoxidase and H₂O₂. High concentrations of elastase and the combined action of H₂O₂ and myeloperoxidase generated a C3b-receptor dysfunction, which implied that the destruction of C3b-receptor function also disturbed Fc-receptor function. The demonstrated C3b receptor dysfunction indicated that the Fc and C3b receptors were closely situated in the cellular membrane of the PMN. A hypothesis for co-operation between the two receptor types would be that the C3b receptor initially facilitates the adherence of an IgG-C3b-coated particle. Secondly, the C3b receptor would facilitate the IgG-Fc-receptor contact either by some kind of structural derangement to permit the entrance of the IgG-C3b complex or by removal of C3b from the Fc part of IgG.     

Exposure to Organic Dust Causes Activation of Human Plasma Complement Factors C3 and B and the Synthesis of Factor C3 by Lung Epithelial Cells <Emphasis Type="Italic">In Vitro</Emphasis>

Exposure in swine confinement buildings induces an intense airway inflammation. Twenty-two volunteers, of whom eleven wore a half-mask, were exposed for 3 hr in a swine barn. Blood samples were drawn before and after exposure. The ratio C3b/totalC3 in plasma decreased from 6.8 to 5.0% (p = 0.02) without mask and from 6.6 to 5.9% (p = 0.01) with mask (p = 0.67 between groups). The ratio Bb/totalB decreased from 14.5 to 13.5% (p < 0.01) without and 14.6–13.3% (p = 0.09) with mask (p = 0.25 between groups). Epithelial cells (A549) incubated up to 24 hr with 0.1 mg/mL dust suspensions were analysed for C3, IL-6 and IL-8 secretion. Cumulative C3 synthesis of dust stimulated cell cultures was 43,000 pg/mL compared to 25,000 pg/mL in unstimulated cells. Cumulative dust-induced IL-6 and IL-8 secretion was 200 and 3000 pg/mL, respectively and below detection in unstimulated cells.The activation of complement in vivo and induced C3 synthesis by epithelial cells suggests a role of complement in the airway reaction to organic dust exposure.     

CD1d-restricted natural killer T cells are potent targets for human immunodeficiency virus infection

Invariant human natural killer T cells (NKT) express a restricted T-cell receptor (TCR) Valpha24Vbeta11 repertoire. These cells share both phenotypic and functional similarities between NK and T cells. Given the emerging role of NKT cells as critical cells in bridging the gap between innate and adaptive immunity, we examined their susceptibility to productive human immunodeficiency virus (HIV) infection by T-tropic, M-tropic, and primary isolates of HIV. We generated three human NKT cell clones (CA5, CA29, and CA31). Phenotypic characterization of these Valpha24+ Vbeta11+ clones indicated that they were predominately positive for CD4, CD161, HLA-DR, CD38, CD45RO, and CD95 expression. The NKT cell clones expressed significantly more surface CCR5 molecules/cell and lower CXCR4 molecules/cell than phytohaemagglutinin-stimulated peripheral blood mononuclear cells (PBMC). Consistent with the surface expression of CCR5 and CXCR4, the NKT clones were also selectively susceptible to HIV M-tropic, T-tropic, and primary isolate infection, as evaluated by both HIV p24 enzyme-linked immunosorbent assay and intracellular staining of HIV proteins. The amount of p24 production was dependent on the NKT clone studied and the HIV strain used. Clones CA29 and CA31 were also susceptible to HIV IIIB infection. The virions produced by these clones were able to productively infect PHA-stimulated PBMCs with the same kinetics as for primary infection of CD4+ blast. Collectively, this data demonstrates that NKT cells can be a target for productive HIV infection but with a lag in the time to peak p24 production.     

Ultrastructural studies on the localization of IgG in the aortic endothelium and subendothelial intima of atherosclerotic and nonatherosclerotic rabbits

Immunoelectron microscopy with peroxidase-conjugated Fab fragments of anti-IgG was used for studying the localization of IgG in the aortic endothelium and subendothelial intima of atherosclerotic and nonatherosclerotic rabbits. Small amounts of IgG were found in the cell coat, in caveolae and vesicles, and also in intercellular clefts of endothelial cells from normocholesterolemic rabbits. Injured endothelial cells exhibited prominent accumulations of IgG in the cytoplasmic matrix, possibly due to leakage through plasma membrane defects. In atherosclerotic lesions from hypercholesterolemic rabbits, there was a striking increase in the amount of IgG-reactive material in the cell coat and vesicles of intact endothelial cells. Also in these animals, injured endothelial cells were characterized by a cytoplasmic IgG accumulation. There were prominent IgG depositions in the subendothelial zone of the lesions. IgG was adhering to collagen fibers, and also coating the surfaces of subendothelial foam cells. The pathophysiological significance of an interaction between such intimal IgG and phagocytes is discussed.     

CT appearance of Varicella Zoster lesions in liver and spleen in an immunocompetent patient.

An adult patient presented with vesicular rash and abdominal pain of 5 days duration. His initial laboratory results showed elevated liver enzymes. A contrast enhanced CT scan demonstrated multiple small hypodense nodules in liver and spleen. His serum was reactive for Varicella Zoster IgM. Patient was treated with intravenous Acyclovir for 5 days and followed up with oral tablets for 2 weeks. At 3 weeks, CT scan showed resolution of hypodense nodules and his serum liver enzymes returned to normal at 6 weeks. Patient is on follow up and asymptomatic for 2 years. The CT appearances of nodules and their resolution following specific antiviral therapy are useful in diagnosis and in follow up of disseminated Varicella Zoster.     

Allergen extracts directly mobilize and activate human eosinophils

Allergic diseases are characterized by the presence of eosinophils, which are recruited to the affected tissues by chemoattractants produced by T cells, mast cells and epithelium. Our objective was to evaluate if allergens can directly activate human eosinophils. The capacity of purified allergen extracts to elicit eosinophil chemotaxis, respiratory burst, degranulation and up-regulation of the adhesion molecule complement receptor 3 (CR3) was determined in eosinophils isolated from healthy blood donors. Eosinophils stimulated with an extract from house dust mite (HDM) released the granule protein major basic protein (MBP) and up-regulated the surface expression of CR3. Cat allergen extracts also induced the up-regulation of CR3, but not the release of MBP; instead cat, as well as birch and grass allergens, elicited the release of eosinophil peroxidase (EPO). In addition, grass pollen extract caused the secretion of MBP. None of the allergens stimulated eosinophilic cationic protein release, nor production of free oxygen radicals. Both HDM and birch extracts were chemotactic for eosinophils. These findings establish that common aeroallergens can directly activate eosinophils in vitro. We propose that eosinophil activation in vivo is not exclusively mediated by cytokines and chemokines of the allergic inflammatory reaction, but could partly be the result of direct interaction between allergens and eosinophils.     

Nonopsonic phagocytosis of erythrocytes infected with ring-stage Plasmodium falciparum

Ring-stage parasitized erythrocytes (RPEs) were demonstrated to interact with effector cells of the innate immune system. With receptor blockade studies and CD36-null macrophages, human and murine macrophages were shown to phagocytose RPEs through the pattern recognition receptor CD36. These in vitro data implicate scavenger receptors in the clearance of RPEs.     

Identification of viral agents associated with diarrhea in young children during a winter season in Beijing, China.

BACKGROUND: Viral diarrhea remains a major cause of childhood morbidity and mortality worldwide. Although rotavirus was extensively studied in China, few comprehensive studies of all viral agents related to diarrhea in children have been conducted. OBJECTIVES: Our study was performed to investigate the role of enteric viruses in acute diarrhea in our country and to evaluate methods that could be used in routine diagnostics. STUDY DESIGN: One hundred stool samples were collected from children under 5 years of age seeking medical care for acute diarrhea during the winter season 2000/2001 in Beijing Children's Hospital. All specimens were initially screened microscopically for leucocytes/red blood cells. Samples with negative results were analyzed for virus presence using commercial EIAs and/or in-house RT-PCRs. RESULTS: At least one viral agent was found in 67% of the specimens. The frequency of rotavirus, astrovirus, norovirus and enteric adenovirus was 59%, 8%, 6% and 2%, respectively. Dual infections were found in 9.0% (6/67) of the positive samples. The results from rotavirus and astrovirus EIAs were concordant with those of rotavirus and astrovirus RT-PCRs. CONCLUSIONS: Enteric viruses play an important role in pediatric diarrhea during the winter season in China. A combination of microscopic examination of stool samples with specific EIA assays to detect virus antigen in stool specimens may be suitable for routine diagnostics.     

The disintegrin/metalloprotease ADAM 10 is essential for Notch signalling but not for alpha-secretase activity in fibroblasts

The metalloprotease ADAM 10 is an important APP alpha-secretase candidate, but in vivo proof of this is lacking. Furthermore, invertebrate models point towards a key role of the ADAM 10 orthologues Kuzbanian and sup-17 in Notch signalling. In the mouse, this function is, however, currently attributed to ADAM 17/TACE, while the role of ADAM 10 remains unknown. We have created ADAM 10-deficient mice. They die at day 9.5 of embryogenesis with multiple defects of the developing central nervous system, somites, and cardiovascular system. In situ hybridization revealed a reduced expression of the Notch target gene hes-5 in the neural tube and an increased expression of the Notch ligand dll-1, supporting an important role for ADAM 10 in Notch signalling in the vertebrates as well. Since the early lethality precluded the establishment of primary neuronal cultures, APPs alpha generation was analyzed in embryonic fibroblasts and found to be preserved in 15 out of 17 independently generated ADAM 10-deficient fibroblast cell lines, albeit at a quantitatively more variable level than in controls, whereas a severe reduction was found in only two cases. The variability was not due to differences in genetic background or to variable expression of the alternative alpha-secretase candidates ADAM 9 and ADAM 17. These results indicate, therefore, either a regulation between ADAMs on the post-translational level or that other, not yet known, proteases are able to compensate for ADAM 10 deficiency. Thus, the observed variability, together with recent reports on tissue-specific expression patterns of ADAMs 9, 10 and 17, points to the existence of tissue-specific 'teams' of different proteases exerting alpha-secretase activity.     

Predominant pathogenic role of tumor necrosis factor in experimental colitis in mice

Antibodies to tumor necrosis factor (TNF)-α have been recently proposed as effective treatment for patients with Crohn's disease. Here, we analyze the functional role of TNF-α in a mouse model of chronic intestinal inflammation induced by the hapten reagent 2,4,6,-trinitrobenzene sulfonic acid (TNBS) that mimics some characteristics of Crohn's disease in humans. Macrophage-enriched lamina propria (LP) mononuclear cells from mice with TNBS-induced colitis produced 10–30-fold higher levels of TNF-α mRNA and protein than cells from control mice. When mice with chronic colitis were treated by intraperitoneal injection of antibodies to TNF-α, an improvement of both the clinical and histopathologic signs of disease was found. Isolated macrophage-enriched LP cells from anti-TNF-α-treated mice produced strikingly less pro-inflammatory cytokines such as interleukin (IL)-1 and IL-6 in cell culture. The predominant role of TNF-α in the mouse TNBS-induced colitis model was further underlined by the finding that striking colonic inflammation and lethal pancolitis was induced in TNF-α-transgenic mice upon TNBS treatment. Conversely, no significant TNBS-induced colitis could be induced in mice in which the TNF-α gene had been inactivated by homologous recombination. Complementation of TNF-α function in TNF^?/? mice by the expression of a mouse TNF-α transgene was sufficient to reverse this effect. Taken together, the data provide direct evidence for a predominant role of TNF-α in a mouse model of chronic intestinal inflammation and encourage further clinical trials with antibodies to TNF-α for the treatment of patients with Crohn's disease.