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Biomedical subjects

A F Michael

Publications and source records attributed to A F Michael.

At least 19 recordsLinked to original sources
PubMed1992

Immunochemical studies of the Alport antigen.

The Alport antigen, a component of normal glomerular basement membranes (GBM) which is absent in Alport familial nephritis, is characterized as a 26 kD non-collagenous (NC1) peptide identified by a monoclonal antibody (Mab A7) and an Alport alloantibody. Both antibodies discriminate X-linkage of the Alport defect using indirect immunofluorescence of hemizygous and heterozygous Alport GBM and epidermal basement membrane (EBM). Immunoblotting of SDS-PAGE gels of collagenase-digested Alport renal BM shows absence of monomeric and dimeric components of the Alport antigen, alpha 3(IV) NC1, and alpha 4(IV) NC1. By immunoprecipitation experiments with specific antibodies, the Alport antigen is distinct from the 26 kD NC1 peptide derived from alpha 1(IV). The monoclonal antibody to the Alport antigen and rabbit antiserum to a non-consensus sequence of alpha 5(IV) NC1 react similarly by immunofluorescence with normal kidney and both fail to bind to Alport renal BM. Two dimension Western blots of collagenase-digested BM show that the anti-Alport antigen and the ant-alpha 5(IV) NC1 react similarly with monomeric and dimeric components of BM collagen. These studies are consistent with the likelihood that the Alport antigen and alpha 5(IV) NC1 are the same or are highly homologous molecules. The precise relationship will require characterization of alpha 5(IV) NC1 protein and determination of the nucleotide sequence of the Alport antigen. The associated absence of alpha 3(IV) NC1 and alpha 4(IV) (NC1) from Alport BM is consistent with other observations for a molecular association of these chains in a novel collagen network.

Antibodies, Monoclonal↗
PubMed1992

Partial protein sequence of the globular domain of alpha 4(IV) collagen chain: sites of sequence variability and homology with alpha 2(IV).

The globular domain (NC) of alpha 4(IV) collagen chain was partially sequenced and compared with the NC domain of other collagen IV chains. The alpha 4(IV) NC domain was found to be most closely related to alpha 2(IV) NC domain but distinct from the NC domain of alpha 1(IV), alpha 2(IV), alpha 3(IV) and alpha 5(IV) collagen chains. Partial sequence, representing nearly one half of alpha 4(IV) NC domain, shows 56%, 69%, 51% and 54% identity with the corresponding NC domains of alpha 1(IV), alpha 2(IV), alpha 3(IV) and alpha 5(IV) collagen chains, respectively. A short, highly polar, region of variable sequence is found near the carboxy terminus of alpha 4(IV) NC domain. This sequence corresponds to a non-conserved region among NC domains, suggesting functional specialization at this site. It exhibits high surface probability with predicted structural differences among NC domains. These results confirm uniqueness of alpha 4(IV) NC domain and indicate its structural relatedness to other NC domains of collagen IV.

Amino Acid Sequence↗
PubMed1992

Explantation of mesangial cell 'hillocks': a method for obtaining human mesangial cells in culture.

A simple method is presented for selective cell culture of human mesangial cells using explantation of mesangial cell hillocks. Glomeruli which had been incubated with collagenase were explanted on plastic tissue culture flasks. Three to 6 weeks after explantation, a rapidly growing multilayer of elongated mesangial cells was observed to grow over the previously established monolayer of glomerular epithelial cells, ultimately forming multiple nodular foci of mesangial cells or 'mesangial cell hillocks'. By explanting mesangial cell hillocks selectively, pure mesangial cell cultures were easily obtained. When compared with mesangial cells grown in mixed cultures from glomerular explants, the hillock-derived cells were identical in morphology, growth characteristics, cell markers and synthesis of extracellular matrix. This system provides a simple method for the isolation of human mesangial cells in culture.

Adolescent↗
PubMed1992

Acute serum sickness in normal and C6 deficient rabbits: role of membrane attack complex.

Acute serum sickness was induced in New Zealand White (NZW) and in C6 deficient (C6D) rabbits, to compare the histology, immunofluorescence, especially distribution of poly C9 (MAC), and electron microscopic characteristics of the disease in each strain. Glomerulonephritis and albuminuria of comparable extent occurred in 13/17 NZW and 4/8 C6D rabbits. In NZW rabbits with albuminuria an early intense glomerular infiltration by mononuclear cells was associated with focal small fine granular glomerular basement membrane (GBM) deposits of IgG and BSA and more diffuse and larger deposits of C3 and MAC. After the disappearance of monocytes and decrease in mesangial cell proliferation, development of large subepithelial GBM deposits rich in all immune reactants was observed in NZB rabbits. In C6D rabbits with albuminuria a similar monocytic infiltrate occurred, but no association with IgG and C3 GBM immune deposits was noted. No deposits of MAC and no large subepithelial GBM 'humps' were observed in C6D rabbits. We conclude that the exudative (monocytic) phase of glomerular injury and albuminuria in acute serum sickness nephritis are not dependent upon terminal complement components, but the subsequent formation of large subepithelial GBM deposits does not occur in this model in the absence of MAC.

Albuminuria↗
PubMed1990

Characterization of type IV collagen NC1 monomers and Goodpasture antigen in human renal basement membranes.

Monomeric subunits of the globular domain of type IV collagen from human renal basement membrane were isolated and characterized. The monomers, M24, M26, M28+, and M28 , which have been identified previously in human glomerular basement membrane, were characterized by amino acid analysis, amino-terminal sequencing, and electrophoretic mobility. The results indicate that M24 and M26 are derived from alpha 1(IV) and alpha 2(IV) collagen chains, respectively. Amino-terminal sequencing revealed that M28+, and M28 correspond to the globular domain of novel collagen chains. M28 has been characterized as the principal target antigen in Goodpasture's syndrome and antiglomerular basement membrane (GBM) nephritis, and both M28 species are absent from the GBM in Alport familial nephritis. The cationic charge of M28 appears to be a consequence of a relatively high concentration of basic amino acids when compared with other monomers. Previous studies of bovine GBM have demonstrated chains with amino-terminal sequence homology to M28+ and M28 .

Amino Acid Sequence↗
PubMed1979

L-asparaginase-induced hypocomplementemia in acute lymphocytic leukemia (ALL) of childhood.

Serum complement studies were carried out in five children with acute lymphocytic leukemia. During therapy with L-asparaginase, prednisone and vincristine, hypocomplementemia developed in all patients, and disappeared within 2 weeks after the discontinuation of L-asparaginase. Complement breakdown products were not present in plasma. The changes of serum complement levels paralleled those of plasma fibrinogen. These findings suggest that the hypocomplementemia observed in these patients may be related to impaired protein synthesis induced by L-asparaginase.

Adolescent↗
PubMed1979

Immunofluorescence studies of dense deposit disease. The presence of railroad tracks and mesangial rings.

Immunopathologic analysis was carried out on renal tissue from patients with membranoproliferative glomerulonephritis, nine with type I and nine with type II (dense deposit disease). A specific finding in all patients with type II, but not type I, was the presence of C3 along the margin but not within the central portion of dense deposit material in the glomerular basement membrane giving a double linear appearance (railroad tracks); C3 was also present within the mesangium, outlining numerous circular structures (mesangial rings). By phase contrast, electron microscopy, and dual label fluorescence studies, the railroad tracks and mesangial rings were shown to outline dense deposit material. Mesangial rings contained properdin (four of nine patients); railroad tracks contained properdin (five of nine patients) and C4 (four of nine patients); no other complement components or immunoglobulins were present. Studies using rhodamine-conjugated rabbit antibody to human glomerular basement membrane demonstrated no reactivity with the dense deposit material itself. In type I and to a lesser extent in type II, granular deposits of C3, C4, properdin, IgM, and IgG were present along the glomerular basement membrane, suggesting that immune complexes play a role in both diseases. Dense deposit transformation of the glomerular basement membrane may be a consequence of a highly specific injury.

Autoantibodies↗
PubMed1979

Spatial orientation and distribution of antigens within human glomerular basement membrane.

Antibodies to GBM have a linear staining pattern along the GBM by immunofluorescence. In this study, we have examined the distribution of human GBM antigens using Goodpasture antibody and heterologous rabbit anti-human GBM antibody. Goodpasture sera and Goodpasture antibody eluted from diseased kidneys reacted as a single linear component within the GBM. Rabbit anti-human GBM was shown to react along distinctly separate zones of the inner and outer aspects of the GBM; the central portion of the GBM seemed to be nonreactive with this antibody. In comparison, Goodpasture antibodies reacted along the inner zone of the GBM but at a locus external to that reacting with heterologous rabbit anti-GBM antibody. These observations of linear binding of antibody to different sites along the GBM suggest a spatial organization of antigen not previously observed.

Anti-Glomerular Basement Membrane Disease↗
PubMed1979

B lymphocyte determinants in immunoglobulin A nephropathy.

Because of our prior demonstration of a strong association betwen a specific B lymphocyte determinant and the occurrence of chronic membranoproliferative glomerulonephritis and the demonstration by others of the frequent concurrence of an IgA deposit disease, anaphylactoid purpura nephritis,with HLA-BW35, we conducted an investigation of the association among Minnesota Caucasians of the HLA markers BW35, DW1 and B lymphocyte determinants identified by three alloantisera with IgA nephropathy and the syndrome of recurrent macroscopic hematuria. The highly significant association between HLA-BW35, DW1, and B cell antigens identified by alloantisera L, B, and F, present in 50 normal Minnesota Caucasians, was not observed in 18 Minnesota patients with IgA nephropathy. The frequency of HLA-DW1 was the same among controls and patients, whereas the relative risk of developing IgA nephropathy was demonstrated to be increased 4- to 5-fold in the presence of the B cell antigens identified by alloantisera L and B. These sera appear to identify determinants on B lymphocytes associated with the disease state and possibly not intimately related to the HLA-D region. These findings emphasize the possible informativeness of defining B cell alloantisera on disease panels.

Antilymphocyte Serum↗
PubMed1978

Collagen synthesis by human glomerular cells in culture.

Collagen synthesis was studied in three subcultured human glomerular cell types, by radiolabeled incorporation of [14C]proline and [3H]lysine. The epithelioid circular glomerular cells secrete a collagen with a single size of chain (possibly type IV) with a high ratio of hydroxyproline to proline, hydroxylysine to lysine, and 11--17% of hydroxyproline as the 3-isomer. The smooth muscle-like rhomboid glomerular cells secrete collagen with a chain pattern suggesting types III and I collagen, distinct from that found in the media of fibroblasts. Small ovoid glomerular cells are morphologically and biochemically intermediate between circular glomerular cells and rhomboid glomerular cells, and may represent an in vitro modification of either circular glomerular cells or rhomboid glomerular cells.

Basement Membrane↗
PubMed1978

Activation of complement by cell surface components of Staphylococcus aureus.

The abilities of intact Staphylococcus aureus H, crude cell walls (CCW), purified cell walls (PCW, peptidoglycan [PG] and covalently linked teichoic acid), peptidoglycan, and cell membranes (CM) to activate the complement system in normal human serum, C2-deficient serum, and immunoglobulin-deficient serum were compared. On a weight basis, PCW was the most active fraction; intact organisms and CCW were about equally effective; and PG was least active in causing complement consumption in normal serum. CM also activated complement but did not give a clear dose-response relationship in the concentrations used. Kinetic studies revealed that C3-C9 consumption occurred at a significantly slower rate in C2-deficient serum, indicating that intact organisms, PCW, and PG may activate the complement system via the classical and alternative pathways in normal serum. C3-C9 consumption was also slower in immunoglobulin-deficient serum than in normal serum, implying that immunoglobulins play a role in attaining maximum rates of complement activation. In all sera studied, PG was less active in complement activation than PCW. These results indicate that a number of cell surface components of S. aureus can play a role in complement activation by this organism and that the presence of teichoic acid has a significant enhancing effect in this regard.

Cell Membrane↗
PubMed1978

Dichotomy between opsonization and serum complement activation by encapsulated staphylococci.

Previous studies have demonstrated that encapsulated Staphylococcus aureus strains are not effectively opsonized by the serum complement system. Encapsulated staphylococci thereby "resist phagocytosis." To test whether this phenomenon might be explained by an inability of encapsulated strains to activate complement, the relationship between staphylococcal opsonization and serum complement activation was studied. Although encapsulation was found to interfere with opsonization by pooled human serum (human polymorphonuclear leukocytes phagocytized significantly fewer encapsulated bacteria than unencapsulated bacteria after incubation in this opsonic source), encapsulated (S. aureus M and Smith diffuse) and unencapsulated (S. aureus M variant and Smith compact) strains had similar capacities for complement activation as measured by C3-C9 consumption. When C2-deficient and immunoglobulin-deficient sera were studied, again C3-C9 consumption was not influenced by the presence or absence of a capsule. In addition, C3 was detected on the surface of both S. aureus M and M variant strains after incubation in pooled serum and staining with fluorescein-conjugated anti-C3 antibody. Thus, encapsulated staphylococci are not effectively opsonized even though complement is activated and C3 is present on the bacterial surface. The exact mechanism by which the capsule interferes with opsonization is still not known; however, inhibition of complement activation appears not to be the explanation of this phenomenon.

Antibodies↗
PubMed1978

The immunohistopathology of glomerular antigens. II. The glomerular basement membrane, actomyosin, and fibroblast surface antigens in normal, diseased, and transplanted human kidneys.

Immunofluorescent studies have demonstrated that actomyosin (AMY) is present in the mesangium in a restrictive pattern, whereas fibroblast surface antigen (FSA) has a more extensive mesangial distribution. Antibody to glomerular basement membrane (GBM) is localized to the GBM. One hundred ninety-six tissue samples, including 17 from normal subjects, 94 from patients with primary renal diseases, and 85 from transplanted kidneys, were examined for changes in distribution of AMY, FSA, and GBM antigens. The distribution of AMY and FSA in the mesangium is markedly increased in width in patients with diabetic nephropathy, and the GBM is thickened. AMY and FSA are mildly increased in patients with glomerulonephritis and GBM is normal. Patients with membranoproliferative glomerulonephritis (MPGN) show a loss of all glomerular antigens. Increased mesangial AMY was found in 12 of 37 transplanted kidneys in diabetic patients vs 4 of 33 nondiabetics 0 to 4 years after transplantation (P < 0.025). This difference is more notable at 2 to 4 years, with 5 of 9 diabetics showing increased AMY vs 0 of 6 nondiabetic patients (P < 0.0005). In MPGN, 5 of 8 tissues showed decreased mesangial AMY vs 3 of 36 diabetic patients (P < 0.0005) and 1 of 32 patients with other glomerulopathies (P < 0.0005). GBM thickening is not associated with specific pretransplant diseases. In transplanted kidneys, the pattern of FSA is dissociated from that of AMY: over half of all patients have increased FSA, even when AMY is normal. Whether this unique finding in transplanted kidneys reflects an increase in the synthesis of FSA by mesangial cells or the failure to clear this (circulating) antigen from the mesangial matrix is unknown.

Actomyosin↗