Characterization of rat liver subcellular membranes. Demonstration of membrane-specific autoantigens

A diagnostic marker of autoimmune chronic active hepatitis: liver plasma membrane antibody in the serum absorbed with particulate fraction of kidney homogenate

The sera absorbed with the particulate fraction of rabbit kidney homogenate (RK) were tested for the antibody against liver plasma membrane (LPM-Ab) by the radiometric assay method. After incubation of the isolated rabbit liver plasma membrane (RLPM) with appropriately diluted serum, IgG bound to RLPM (IgG-RLPM) was determined using 125I-labelled Staphylococcal protein A. IgG-RLPM in each subject tested was expressed in arbitrary units, that is, the multiple of the mean radioactivity associated with RLPM in 35 control subjects. Thus IgG-RLPM was 1.00 (mean) +/- 0.23 (SD) in the control subjects, 1.13 +/- 0.30 in 9 patients with chronic persistent hepatitis (CPH), 1.13 +/- 0.52 in 15 with chronic active hepatitis (CAH), 1.34 +/- 0.38 in 23 with liver cirrhosis (LC) and 3.45 +/- 0.73 in 5 with autoimmune CAH. F(ab')2 fragments from a patient with autoimmune CAH and a control subject decreased IgG-RLPM by 86.4 +/- 6.35 and -5.2 +/- 14.9%, respectively, in four patients with autoimmune CAH. LPM-Ab was detected in 0, 20.0 and 17.4% in the patients with CPH, CAH and LC, respectively. All of the patients with autoimmune CAH were positive for LPM-Ab. The absorption of the sera positive for LPM-Ab with RK decreased IgG-RLPM in various extents. In two of five patients with autoimmune CAH and two of seven patients with CAH or LC, the majority of LPM-Ab was cross-reactive with RK.

Human monoclonal antibody recognizing liver-type aldolase B

A human hybridoma clone (4E3) has been established by fusing lymphocytes from a lymph node taken from a breast cancer patient and human lymphoblastoid cells, LICR-LON-HMy2, by the poly(ethylene glycol) method. 4E3 has been stabilized and continued to secrete IgMk antibody into culture medium (greater than 10 micrograms/ml) for over 1 year. The following characteristics of the antigen strongly suggested that 4E3 recognizes liver-type aldolase B (EC 4.1.2.13): the Mr of the native molecule is 160,000 and that of the subunit is 40,000, and thus it has a tetrameric structure of identical subunits; the antigen is abundant in the liver and kidney of human, mouse and rabbit, and is localized by immunohistochemical methods in the cytoplasm of hepatocytes and in the proximal tubules of the kidney; the antigen is precipitable by 50-80% saturation with (NH4)2SO4; the antigen shows charge-dependent heterogeneity on DEAE-cellulose chromatography. To confirm this notion, aldolase B was purified to homogeneity from the liver of human, mouse and rabbit by phosphocellulose chromatography. During the chromatographic purification, the antigen activity as assayed by enzyme-linked immunosorbent assay (e.l.i.s.a.) was superimposed on the enzymic activity of aldolase. Furthermore, monoclonal antibody 4E3 strongly reacted with purified aldolase B in SDS/polyacrylamide-gel electrophoresis followed by Western blotting and also in e.l.i.s.a. using microplates coated with purified enzyme. The reaction between aldolase B and 4E3 activated the human complement system as assessed by the attachment of C3 to the immune complex of aldolase B and 4E3.

The dynamics of membrane structure

The membranes of living organisms are involved in many aspects of the life, growth and development of all cells. The predominant structural elements of these membranes are lipids and proteins and the basic strucvture of these molecules has been reviewed. The physical properties of the lipid constituents particularly their behavior in aqueous systems has led to the concepts of thermotropic and lyotropic mesomorphism; the interaction between different types of lipid molecules modulate this behavior. Interaction of phospholipids in aqueous systems with cholesterol, ions and drugs have been examined in this context. In addition a variety of model lipid-protein systems have been investigated and the implications of interactions between lipids and different proteins in biological membranes has been evaluated. This leads to a detailed consideration of the way lipids and proteins ae organized in cell membranes and contains an appraisal of the evidence supporting contemporary views of membrane structure. Particular attention has been devoted to the question of how mobile the components are within the structure. Particular attention has been devoted to the question of how mobile the components are within the structure. Finally the biosynthesis, turnover and modulation of the properties of interacting membrane constituents is critically reviewed and possible ways of controlling the behavior of cells and organisms by altering the structural parameters of different membranes has been considered.

Characterization of autoantigenic sites on isolated dog heart mitochondria

1. Anti-heart mitochondria autoantibodies were developed in serum from dogs following experimental myocardial infarction. 2. Heart mitochondria frozen and thawed repeatedly in a sucrose/Tris-chloride buffer retained both their functional integrity as measured by the respiratory control ratio and their ability to serve as an antigen in a complement fixation test. Mitochondria frozen and thawed in a potassium chloride/Tris-chloride buffer lost both their functional integrity and their autoantigenic activity after one freeze-thaw cycle. 3. Extraction of the heart mitochondria with acetone/water mixtures to remove phospholipids from the membrane led to a complete loss of the ability of the mitochondria to react in the complement fixation test but did not affect the ability of the membranes to bind autoantibody in absorption experiments. 4. Treatment of the mitochondrial membranes with increasing concentrations of trypsin caused a loss of up to approximately 50% of the membrane protein with a gradual decrease in the autoantigenic activity of the membrane without impairment of the ability of the membrane to bind autoantibody. 5. Removal of up to 90% of the sialic acid of the mitochondrial membrane with neuraminidase resulted in a considerable increase in the complement-fixing autoantigenic activity of the membrane without changing the apparent ability of the membrane to bind autoantibody in absorption experiments. 6. Exposure of mitochondrial membranes to autoantibody and complement caused an inhibition of both an inner mitochondrial membrane enzyme, i.e. cytochrome oxidase (48%) and an outer mitochondrial membrane enzyme, i.e. NADH cytochrome c reductase (rotenone insensitive) (37%).

Characterization of anti-heart mitochondria autoantibodies produced in dogs following myocardial infarction

A complement-fixing, heart-reactive serum component that develops in dogs following experimental myocardial infarction was characterized with respect to its immunoglobulin nature and its subcellular membrane and organ specificities. The immunoglobulin nature of the heart-reactive serum factor was established by the following evidence: (1) the factor was not removed from the serum following absorption of up to 90% of the first component of dog complement with bovine serum albumin (BSA)-anti-BSA immune precipitates, (2) the serum factor sedimented in the 19S region of sucrose density gradients, and (3) affinity chromatography using a Sepharose column coupled with rabbit anti-dog µ-chain-specific antibody resulted in the removal of nearly all of the heart-reactive substance. The major subcellular autoantigenic locus of the dog heart was determined to be the outer mitochondrial membrane. Serum containing the autoantibody demonstrated a six-fold greater autoantibody titer when outer mitochondrial membrane was used as the test antigen than it did when inner mitochondrial membrane was used. Absorption experiments suggested that the autoantigenic determinants residing on inner and outer mitochondrial membranes were unique to the individual membranes. Significant cross-reaction of the anti-heart autoantibody between heart and skeletal muscle mitochondria was observed, but no cross-reaction was seen with dog liver mitochondrial membranes.