Biomedical subjects

N Amos

Publications and source records attributed to N Amos.

85 records · Page 5Linked to original sources

PubMed1984

The influence of HLA-linked genes on the severity of anti-GBM antibody-mediated nephritis.

Thirty-nine Caucasian patients with glomerulonephritis caused by autoantibodies to glomerular basement membrane (GBM) were studied. They were segregated into three groups depending on presentation: Group 1 (19 patients) were anuric or oliguric, group 2 (13 patients) had rapidly deteriorating renal function but were not oliguric, and group 3 (seven patients) had stable renal function. The incidence of HLA-DR2 was greatly increased; it was present in 34 of 38 patients in whom DR antigens were identified compared to 43 of 154 controls (Pc = 0.63 X 10(-8), relative risk 36, etiological fraction 0.86). The incidence of HLA-B7 was also increased; present in 23 of 39 patients and 43 of 193 controls (Pc = 0.26 X 10(-4), relative risk 5.0, etiological fraction 0.43). These data were analyzed for a third order association between HLA-DR2, HLA-B7, and anti-GBM disease. Such an association was probable for patients in group 1 (P = 0.27 X 10(-6), likely for those in group 2 (P = 0.024) but unlikely for patients in group 3 (P = 0.62) suggesting HLA-B7-associated genes influence severity. Clinical results from a subset of the patients referred directly on presentation showed that patients who inherited HLA-B7 together with DR2 had significantly higher plasma creatinines, a greater proportion of glomeruli surrounded by crescents and a worse prognosis. Despite this there was little difference in severity of their lung disease.

Adolescent↗

PubMed1984

C4-binding protein in sera of patients with systemic lupus erythematosus and mixed essential cryoglobulinemia.

C4-binding protein (C4BP) concentration was measured in sera of patients with systemic lupus erythematosus (SLE) (59) and mixed essential cryoglobulinemia (MEC) (6). The mean concentration of C4BP was not significantly different from the normal controls in both groups of patients; 1 patient with MEC and 11 patients with SLE had concentrations below the normal range. In addition there was no significant correlation between C4BP and C3, C4 or factor B concentrations in patients with SLE. These results suggest that C4BP is not consumed in these two diseases where strong activation of the classical pathway is known to occur in vivo. In addition, the significantly increased C4BP/C4 ratio, evident in both groups of patients, may provide a protective mechanism against C3 conversion by the classical pathway.

Carrier Proteins↗

PubMed1983

Metabolism of IgG in type II mixed essential cryoglobulinaemia--autologous cryoprecipitated and normal homologous IgG are incorporated into complexes and metabolized in vivo at similar rates.

The metabolism of autologous cryoprecipitated and normal homologous IgG was studied in four patients with type II mixed essential cryoglobulinaemia. 131I-autologous IgG purified from each patient's cryoglobulin (Cryo-IgG), and 125I-pooled normal homologous IgG (N-IgG) were studied simultaneously to compare the extent of their incorporation into complexes with IgM in vitro and in vivo, and their turnover in vivo. A proportion of each preparation of IgG was incorporated into macromolecular complexes in vitro and in vivo in all patients, the Cryo-IgG only slightly more so than N-IgG. Results of the turnover studies were heterogeneous, but the common finding was the absence of any significant difference in the metabolism of Cryo-IgG and N-IgG. In two patients the fractional catabolic rates (FCR) of Cryo-IgG and N-IgG were increased and in one they were normal. The fourth patient was also hypogammaglobulinaemic (IgG 0.52 mg/ml) and it was shown that in vivo virtually all his IgG was combined with IgM; despite this the FCR of both types of IgG was reduced. These results suggest (1) that the IgG component of the cryoglobulins in these patients is unlikely to differ significantly from normal IgG and (2) that, contrary to expectation, complexed IgG is not necessarily rapidly eliminated from the circulation.

Aged↗

PubMed1981

The role of carbohydrate in the structure and function of nephritic factor.

Six nephritic factors (NeFs) were purified from the IgG fraction of sera of patients with PLD and/or MPGN by elution from EA C43bBb. All had at least one abnormal H chain component when examined by PAGE-SDS and two additionally had a large L chain. Four different H chains were found. Their apparent molecular weights and the frequency with which they occurred were: 65,000 (one NeF), 61,500 (four NeFs), 57,000 (two NeFs) and 55,000 (one NeF) compared with 53,500 daltons for normal H chain. The molecular weight of the large L chains was 26,500 daltons (cf. 23,500 for normal L chain). Both the NeF activity and the large components were located in the F(ab')2 fragment of the molecule and after reduction the large component was found in the Fd fragment of the H chain. Neuraminidase treatment of purified NeF caused a 1-2% decrease in apparent molecular weight of the large H chain on PAGE-SDS. Mild periodate oxidation, sufficient to cause primarily loss of carbohydrate, caused a marked loss of activity. Reduction and alkylation of NeF under neutral conditions caused only a small loss of activity but after acid dissociation the H and L chains were completely inactive.

Autoantibodies↗

PubMed1978

The immunogloblin nature of nephritic factor (NeF).

NeF was shown to be antigenically and structurally similar to IgG by the following experiments: (1) NeF activity in serum was absorbed by and, under acid conditions, could be eluted from (a) anti-myeloma IgG antibody coupled to Sepharose and (b) protein A-Sepharose. (2) Purified NeF could bind to anit-myeloma IgG-Sepharose and could be eluted with acid, and this binding was blocked by myeloma IgG. (3) An antibody to beta2, microglobulin, showing strong cross-reactivity with normal IgG, bound NeF activity before, but not after, absorption of the antiserum with IgG. (4) Sepharose-coupled antibodies to NeF could bind activity which was recovered in the acid eluate. This binding capacity was lost after absorption of the antibody with normal and myeloma IgG. (5) Structural similarity was demonstrated by pepsin and papain digestion, which resulted in NeF activity eluting with F(ab')2 and Fab fragments from protein A-Sepharose and Sephadex G-150. (6) Autoradiography of PAGE-SDS of 125I-labelled NeF eluted from EA43bBb cells showed that NeF had a larger H chain than normal IgG, suggesting that NeF might be an abnormal IgG molecule.

Chemical Phenomena↗

PubMed1977

Metabolism of the fifth component of complement, and its relation to metabolism of the third component, in patients with complement activation.

The metabolism of the fifth component of complement (C5), and its relatonship to metabolism of the third component of complement (C3), has been studied in normal subjects and patients by simultaneous administration of radioiodine labeled C5 and C3. In seven normal subjects the fractional catabolic rate of C5 ranged from 1.5 to 2.1% of the plasma pool/h and extravascular/intravascular distribution ratio from 0.22 to 0.78, these values being similar to those obtained for C3, and synthesis rate from 71 to 134 mug/kg per h, In patients with complement activation the increase in fractional catabolic rate of C5 was nearly always less than that of C3. The data also showed that there was increased extravascular distribution of C3 and C5 in most patients and considerable extravascular catabolism of both proteins in some. However, there were differences in metabolic parameters between patients with different types of complement activation. In patients with systemic lupus erythematosus, fractional catabolism and extravascular distribution of C3 and C5 were both increased, and there was marked extravascular catabolism of both proteins. There was increased fractional catabolism and extravascular distribution of C3 in patients with mesangiocapillary nephritis and (or) partial lipodystrophy, and fractional catabolism of C5 was also increased in three of six studies although distribution of C5 was always within the normal range; however, in two patients with nephritic factor in their serum fractional catabolism of C5 was normal despite markedly increased C3 turnover, suggesting that in patients with alternative pathway activation by nephritic factor little or no C5 convertase is generated.

Adolescent↗

PubMed1977

C3b receptors in glomerular disease.

Using two indicator systems--sheep erythrocytes or fluoresceinated S. typhi coated with C3b the presence of a receptor for C3b (but not C3d) in the normal human glomerulus is confirmed. No receptor could be detected in other species tested (mouse, rat, guinea-pig, rabbit and rhesus monkey). Binding of indicator particles was reduced or lost in diseases associated with glomerular capillary deposition of C3, but not in those with mesangial deposition alone. However in some cases the receptor was lost in the absence of detectable C3 deposition. No receptors were detected in proliferating cells in glomerular crescents.

Animals↗

PubMed1977

Guinea-pig nephrotoxic nephritis II. Autologous phase: complement activation without detectable injury.

In the autologous phase of nephrotoxic induced by sheep antibody to glomerular basement membrane (GBM) in Dunkin-Hartley and C4 deficient strain guinea-pigs, less than 50% of animals developed proteinuria at the height of the autologous antibody response despite high anti-sheep immunolglobulin tetres and fixation of guinea-pig IgG and complement in the kidney. tonly two of thirty-sdven animals (5-4%) developed progressive. In a passive model of autologous phase injury using high titres rabbit antibody to sheep IgG, proteinuria failed to occur despite fixation of up to 95 microng rabbit antibody per kidney. Repeated injection of sheep nephrotoxic antibody (NTab) caused a persisting nephrotic syndrome but not the characteristic proliferative lesion of anti GBM diseases in other species.

Animals↗

PubMed1976

The complement abnormalities of lipodystrophy.

Investigation of the serum complement system in 25 patients with various forms of lipodystrophy showed no abnormality in three patients with total lipodystrophy; a single patient with limb lipodystrophy had evidence of activation of the classical complement pathway. However, of the 21 patients with partial lipodystrophy, 17 had low serum C3, with normal C4 and C2, concentrations, accompanied in 14 by a serum C3 splitting factor indistinguishable from nephritic factor, suggesting activation of the alternative pathway. These abnormalities occurred in 10 patients without clinically overt renal disease. Seven patients had overt nephritis; renal biopsies obtained in six showed mesangiocapillary (membranoproliferative) nephritis in all. Thus, the majority of patients with partial lipodystrophy have hypocomplementemia. Although nephritis may not invariably develop, the high rate of mesangiocapillary nephritis in these patients suggests that complement activation via the alternative pathway predisposes to the development of this form of glomerular disease.

Adolescent↗

PubMed1976

The cofactors required by C3 nephritic factor to generate a C3 convertase in vitro.

The mechanisms by which a C3 convertase is generated by C3 nephritic factor (NeF) were investigated using purified NeF, C3, C3b, factor B and factor D of the alternative pathway of complement activation. NeF could generate a C3 convertase with C3 and B in the absence of D, and without cleavage of B. At lower concentrations of NeF the addition of D was required to generate a C3 convertase, and B cleavage now occurred. The generation of both the D-independent and D-dependent C3 convertases with NeF was inhibited by preincubation of the C3 source with C3b inactivator (KAF); isolated C3b was more efficient than the C3 preparations used in generating the D-independent C3 convertase with NeF. These experiments indicate that C3b is required for the formation of both convertases, and that the reaction occurring with apparently native C3 is due to trace amounts of C3b. It is concluded that the C3 convertase generated by NeF in the absence of D is C3bB (NeF), and that generated in the presence of D is the feedback convertase C3bBb. The relevance of these experiments to reactions which may occur in vivo is discussed.

Biological Products↗

PubMed1975

Guinea-pig nephrotoxic nephritis. I. The role of complement and polymorphonuclear leucocytes and the effect of antibody subclass and fragments in the heterologous phase.

In guinea-pig nephrotoxic nephritis induced by a sheep antibody there was minimal glomerular capillary deposition of C3 and accumulation of polymorphonuclear leucocytes (PMN) in the heterologous phase. The C4-deficient strain developed the same injury as normal Duncan-Hartley animals. Complement depletion with cobra venom factor, polymorph depletion with nitrogen mustard or anti-PMN serum and treatment with antihistamines provided no protection. The relationship between the dose of nephrotoxic antibody and the proteinuria was similar for gamma1 and gamma2 subclasses and the F(ab')2 fragment of gamma1 antibody. However, the F(ab') and F(ab) antibody fragments, though fixing on the glomerular basement membrane, did not cause proteinuria. It is concluded that the development of proteinuria in this system: is largely independent of the complement-polymorph system; is due to the fixation of the F(ab')2 fragment of the antibody molecule; and does not depend on an intact Fc piece.

Animals↗

PubMedDate not supplied

Effect of liposome surface charge on the stability of technetium (99mTc) radiolabelled liposomes.

Using liposomes radiolabelled by the 99mTechnetium-stannous chloride technique we have investigated the effect of surface charge on the stability of the isotope in vitro and in vivo. Dialysis of 99mTc-labelled positive, negative and neutral liposomes, which had been incubated in either saline or normal rat serum showed no significant loss of the isotope from the liposome surface with only 2 per cent of the isotope dialysed. A comparison of gel chromatography with dialysis confirmed that most of the isotope remained attached to the liposome surface, but it did reveal greater loss of the isotope, between 15 and 23 per cent. The liposome clearance rates obtained from 125I-egg phosphatidylcholine (EPC) and 99mTc dual-labelled positive or neutral liposomes were significantly different. The 99mTc marker was cleared five times faster from the positive liposomes and twice as fast from the neutral liposomes as the 125I-EPC integral membrane marker. The 99mTc attached to liposomes with a negative surface charge was stable in vivo and had the same clearance rate from the circulation as the 125I-EPC marker. These results indicate that the commonly used in vitro techniques for assessing liposome radiolabel stability are unsuitable for predicting the stability of the 99mTc in vivo.

Animals↗

PubMedDate not supplied

High performance liquid chromatographic analysis of liposome stability.

Two techniques have been studied for their suitability for the analysis of the stability of liposomes: (1) High Performance Gel Permeation Liquid Chromatography (HPGPLC), a TSK G5000PW Ultrogel column; (2) Gel Permeation Chromatography (GPC), a Sepharose 4B column. The stability of dual radio-labelled, cholesterol-poor and cholesterol-rich, negatively charged liposomes in vitro (in saline and in serum), and in vivo, have been investigated using these two techniques. The HPGPLC TSK G5000PW column proved to be the superior technique for the analysis of liposome stability with the advantages of rapid run times, increased sample recovery, and smaller sample volumes were required. The results obtained confirm that inclusion of a high ratio of cholesterol into the liposome structure prevents phospholipid loss when exposed to serum, and that the cholesterol-poor liposome structure is dramatically altered under the same conditions. In conclusion, the TSK G5000PW column is ideal for monitoring movement of phospholipid between liposomes and serum proteins and for detecting changes in liposome size.

Animals↗