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Biomedical subjects

M R Daha

Publications and source records attributed to M R Daha.

At least 487 records · Page 27Linked to original sources
PubMed1976

Control of the amplification convertase of complement by the plasma protein beta1H.

An inhibitory activity for an erythrocyte in termediate bearing the properdin (P)-stabilized amplification C3 convertase, PC3bBb, was recognized in whole normal human serum and separated from C3b inactivator by its distinct physicochemical and functional characteristics. The inhibitory activity was found to reside in a protein that was purified to homogeneity and elicited a monospecific antibody in a rabbit. This protein was identified as beta1H and found to have a serum concentration of 516 +/- 89 mug/ml (mean +/- 1 SD). beta1H produced a dose related, first-order loss of convertase function and release of 125I-Bb from the P-stabilized intermediate, indicating a mechanism of action by decay-dissociation of Bb from the complex, PC3bBb. beta1H exhibited only a limited capacity to accelerate decay of C3bBb sites stabilized with C3 nephritic factor or to release 125I-Bb from such sites. Amplification of C3 cleavage by C3bBb may well determine whether initial complement activation by the classical or alternative activating sequence is beneficial or detrimental to the host. Regulation of this amplifying function is now recognized to occur at at least three steps: intrinsic decay which reflects the inherent lability of the C3bBb convertase; extrinsic decay-dissociation of Bb which is mediated by the effect of beta1H; and inactivation of exposed C3b by C3b inactivator. The stabilization of C3bBb by activated properdin minimizes intrinsic decay and protects C3b in the bimolecular complex from C3b inactivator. beta1H restores control of the system by decay-dissociation of the bimolecular complex, therby exposing C3b to C3b inactivator whose irreversible action prevents regeneration of the convertase at that site.

Animals↗
PubMed1976

The natural modulation of the amplification phase of complement activation.

As C3 cleavage represents the most critical step in the elaboration of the biologic effects of the complement system, the modulation of this reaction by formation and function of the C3b-dependent C3 convertase may well determine whether the initial activation of the complement sequence eventuates in beneficial or detrimental effects to the host. Stabilization of the amplification C3b-dependent convertase, C3bBb, is achieved with P and C3NeF, respectively, after their binding which exhibits different molecular and temperature requirements. Control of this amplifying step occurs at three levels: intrinsic decay of the inherently labile C3bBb convertase; extrinsic decay by displacement of Bb from the convertase with beta1H; and inactivation by C3bINA of C3b after its generation from native C3 or removal of protective Bb by intrinsic or extrinsic decay. In the presence of the stabilizing factors the control proteins must function in sequence with beta1H-mediated decay preceding C3b inactivation.

Complement C3↗
PubMed1976

C3 nephritic factor (C3NeF): stabilization of fluid phase and cell-bound alternative pathway convertase.

C3 nephritic factor (C3NeF) defined by the capacity of nephritic serum and its fractions to initiate loss of the B antigen of C3 in normal serum was purified from the serum of three different donors and shown to function by stabilization of membrane-bound and fluid phase alternative pathway C3 convertase. C3NeF converts cell-bound C3B sites in a dose-related manner to CEB(NeF) sites, which exhibit an approximate 10-fold increase in half-life. The linear relationship between the C3NeF input and the residual hemolytic sites on EAC43B present after incubation for 20 min at 30 degrees C, during which labile C3B sites have decayed, indicates that the number of residual C3B sites is directly related to the dose of C3NeF. The capacity of C3NeF to stabilize the C3B convertase in a temperature- and dose-dependent manner, which is independent of binding or consumption of C3NeF, in a fluid phase reaction mixture of 125I-B, 131I-C3 and D permits isolation of a 10S complex containing radiolabeled C3 and B and exhibiting C3, convertase activity on an exogenous C3 source. Thus, the stabilizing effect of C3NeF is not limited to membrane-bound C3B but is also sufficient to permit recovery of a fluid phase C3 convertase formed during the interaction of C3, B, and D.

Binding Sites↗
PubMed1976

C3 requirements for formation of alternative pathway C5 convertase.

Although alternative pathway C3 and C5 convertases both have active proteolytic sites dependent on the same protein, Bb, the quantitative requirements for the expression of these activities are sufficiently different to permit their delineation in terms of B input an cell-bound C3b. That the labile component of each active site is Bb was established by their parallel decay rates, regeneration of the original specificities with B in the presence of D, and stabilization of each convertase by C3NeF. The evidence that the spatial relationships of Bb and C3b on the cell surface for C3 and C5 convertase activities are distinct is based not only upon the decay and regeneration of each original convertase but more so upon their interconversion. C3 convertase is converted to C5 convertase by interaction with additional C3 whereas C5 convertase reverts to a C3 convertase by treatment with C3 INA. The capacity of C3 INA treatment to abolish C5 convertase sites without affecting C3 convertase sites indicates the existence of two functional species of C3b, one of which is protected in the C3bBb complex whereas the other is exposed.

Cell Membrane↗
PubMed1976

Formation in the presence of C3 nephritic factor (C3NeF) of an alternative pathway C3 convertase containing uncleaved B.

C3 nephritic factor (C3NeF) interacts with native C3 and B in the absence of D to generate a C3 convertase containing an uncleaved form of B. Dose response studies with C3NeF and B, respectively, revealed incremental C3 inactivation without loss of B. These findings are in agreement with the previous isolation from such reaction mixtures of a 10S complex containing haemolytically inactive C3 and active B and manifesting C3 convertase activity. Functional contamination of C3 with C3b was negated by demonstrating that pretreatment of C3 with C3bINA had no effect on its subsequent interaction with B and C3NeF to generate C3 convertase activity, while pretreatment of C3b eliminated its effective interaction with B and C3NeF. Relatively higher concentrations of C3bINA present during interaction of C3, B and C3NeF suppressed C3 inactivation, indicating its dependence on amplification by utilization of the initial C3b generated. Trace quantities of D were not found by functional analyses of C3, B and C3NeF and pretreatment of these proteins with a concentration of DFP sufficient to suppress D activity had no effect on their effective interaction. The introduction of D to mixtures of C3NeF, B, and C3 resulted in B clevage and more efficient expression of C3 convertase function as defined by a reduced requirement for C3NeF.

Complement C3↗
PubMedDate not supplied

Complement-endothelial cell interactions: pathophysiological implications.

The function of the endothelial cells can be modulated by humoral factors present in the circulation and in the extravascular fluid, including proteins of the complement system. This review examines the multiple interactions between the complement system and the endothelial cells and their functional consequences on inflammation, coagulation and regulation of vascular tone. The implications of these interactions in the induction and progression of the vascular lesions occurring in atherosclerosis, ischemia/reperfusion and xenotransplantation and the possible therapeutic approaches in terms of complement regulation are also discussed.

Animals↗
PubMedDate not supplied

Production of inflammatory mediators and cytokine responsiveness of an SV40-transformed human proximal tubular epithelial cell line.

Proximal tubular epithelial cells (PTEC) play a central role in the physiology of the renal tubulointerstitium. To be able to study the relationship between tubular cells and inflammatory renal diseases the availability of cultured cells is of importance. This study describes an immortalized proximal tubular epithelial cell line which was generated using SV40 DNA. To determine whether the transformation altered the cell line, the transformed cell line was characterized phenotypically using different monoclonal antibodies directed against peptidases, which are characteristic of PTEC, such as adenosine deaminase binding protein (CD26), leucine amino peptidase and carboxy peptidase M by immunofluorescent staining and FACS analysis. All peptidases were clearly present on the parental cell line and the transformed cell line. However, the level of expression of the peptidases was lower on the transformed cell line as compared to the parental nontransfected cells. The morphology of the transformed cell line, determined using a transwell culture system and electron microscopy, showed a polarized morphology of the tubular cells, tight junctions and microvilli. The transformed cell line was compared with the parental proximal tubular epithelial cells in its ability to respond to inflammatory cytokines such as IL- 1alpha TNF-alpha, IFN-gamma. Stimulation with these cytokines resulted in enhanced production of complement components C2, C3, C4 and factor H, IL-6 and the chemokines IL-8 and MCP-1. The transformed cell line responded in a similar fashion as the parental cell line, although the amount of the different proteins produced was significantly higher in the transformed cell line. Overall, the transformed tubular cell line seems to be a suitable model to study different effects on tubular cells in relation to inflammatory kidney diseases.

Blotting, Southern↗
PubMedDate not supplied

Tubular epithelial cells: A critical cell type in the regulation of renal inflammatory processes.

Most chronic human kidney diseases are characterized by a final common pathway consisting of interstitial inflammation and ultimately leading to interstitial fibrosis. Within this process, tubular epithelial cells (TECs) play a critical role. Both in vitro and in vivo it has been demonstrated that TECs are an important source of various cytokines, chemokines, growth factors, adhesion molecules and extracellular matrix components. In the present review we will outline the capacity of TECs to produce inflammatory mediators and discuss the different mechanisms involved in the regulation of production of these mediators.

Animals↗
PubMedDate not supplied

Immunological function of tubular epithelial cells: the functional implications of CD40 expression.

Tubulo-interstitial inflammation in the kidney is characterized by the presence of activated T cells. Both by the local production of cytokines, as well as by direct cell-cell interactions, these activated T cells might affect the immune and inflammatory response. Recently it has been demonstrated that these kidney-infiltrating T cells express CD40 ligand and that tubular epithelial cells (TECs) express CD40. In the present review we will discuss the potential implications of CD40-CD40L interactions for the activation of TECs and its immunological function.

Animals↗
PubMedDate not supplied

Induction of renal cell apoptosis by antibodies and complement.

Renal diseases are in many cases associated with the presence of increased numbers of apoptotic cells in the kidney. Apoptosis has been proposed as an important mechanism involved in the resolution of a proliferative response. Furthermore, recent studies indicate its possible involvement in progression of renal disease, leading to sclerosis. Moreover, in an experimental model of acute mesangioproliferative glomerulonephritis in the rat, induced via antibodies directed to Thy-1, evidence was obtained for the occurrence of apoptosis coinciding with the very early induction of mesangial injury. The present review is focused on apoptosis in relation to this model, and discusses recent findings concerning direct involvement of triggering of Thy-1 as well as deposition of terminal complement complexes in the induction of mesangial cell apoptosis.

Animals↗
PubMedDate not supplied

Mechanisms of mesangial injury in glomerular diseases.

Immune-mediated mesangial cell injury can be triggered by various mechanisms including the trapping of immune complexes, binding of specific antibodies to mesangial cells or indirect binding of immune complexes to mesangial cells via specific receptors. These receptors include specific receptors for IgG or IgA and complement receptors. Interactions of immune complexes or antibodies with mesangial cells contribute to activation of these cells and release of cytokines and chemokines, influx of inflammatory cells and either further activation of intrinsic renal cells or injury of the glomerulus. In this review a number of aspects of renal cell injury are summarized.

Animals↗
PubMedDate not supplied

Isolation, culture, characterization and use of human renal tubular epithelial cells.

Tubulointerstitial alterations are a hallmark of most renal diseases. In vitro culture of different cell types of the tubulointerstitial compartment have been instrumental in studying their respective contributions to the inflammatory and fibrotic process. The present paper provides an overview of the isolation, culture and characterization of tubular epithelial cells, with a main emphasis on cells from human origin.

Cell Culture Techniques↗
PubMedDate not supplied

High levels of antibodies against Clq are associated with disease activity and nephritis but not with other organ manifestations in SLE patients.

OBJECTIVE: Serum concentration of antibodies to C1q (C1qAb) has been reported to be elevated in a high percentage of patients with systemic lupus erythematosus (SLE). The associations of high C1qAb levels with different clinical manifestations and the activity of the disease, however, are not definitely understood. METHODS: We measured the levels of IgG type C1qAb in the sera of 137 patients with SLE using an ELISA method. RESULTS: Serum concentrations of C1qAb were found to be higher (p < 0.0001) in SLE patients than in healthy controls. High titer (> 66 AU/ml) C1qAb was found in 40/137 (29.2%) SLE patients, and 4/192 (2.1%) healthy controls (p < 0.0001). A strong negative correlation (R = -0.4, p < 0.0001) between the age of the patients and the C1qAb titers could be detected. C1qAb levels in clinically active SLE patients significantly (p < 0.0001) exceeded those measured in the sera of patients in the inactive stage of the disease. A significant positive correlation was detected between C1qAb levels and the laboratory activity markers (anti-DNA, low C3 level) of the disease. We found a significant negative correlation between levels of C1qAb and a negative acute phase protein, alpha2-HS-glycoprotein. Renal involvement was present in 11/40 (27.5%) and 11/97 (11%) of the patients with high and low titers of C1qAb, respectively (p = 0.038). The prevalence of other organ manifestations was, however, the same in the patients with or without high titer C1qAb. CONCLUSION: These findings indicate that C1qAb measurement is a useful method for detecting the activity of SLE and predicting renal manifestations, but not other organ involvement in the disease.

Adult↗
PubMedDate not supplied

IgG and IgA autoantibodies to C1q in systemic and renal diseases.

Antibodies to the collagen-like region of C1q have been described in patients with SLE and rheumatoid vasculitis. In this study the prevalence of both IgG and IgA C1qAb was assessed in serum samples of 385 patients with different systemic and renal diseases. The results demonstrate that the prevalence of IgG and IgA C1qAb is not restricted to the diseases in which they were originally described. C1qAb can also be demonstrated in patients with MCTD, Felty's syndrome, ankylosing spondylitis, polyarteritis nodosa, mixed cryoglobulinaemia, membranoproliferative glomerulonephritis, glomerulosclerosis, and patients with anti-glomerular basement membrane nephritis. The widespread occurrence of C1qAb of both immunoglobulin classes in systemic and renal diseases may provide insight into the mechanisms that lead to C1qAb formation.

Arthritis, Rheumatoid↗