A fetal protein in chromatin of Novikoff hepatoma and Walker 256 carcinosarcoma tumors that is absent from normal and regenerating rat liver

Antibodies to chromatin proteins of Novikoff hepatoma cells formed precipitin bands in the double-diffusion immunoprecipitation assay with chromatin proteins of Novikoff hepatoma, Walker 256 carcinosarcoma, and 18-day fetal rat liver. The antigen used for preparation of antiserum was the chromatin proteins initially extracted with 3 M NaCl-7 M urea and soluble after dialysis to 0.14 M NaCl-0.35 M urea. The chromatin proteins used for analytical studies were extracted with 0.6 M NaCl containing 0.01 M Tris-HCl (pH 8) and 100 muM phenylmethylsulfonyl fluoride. Corresponding chromatin proteins of normal and 18-hr regenerating rat liver, heart, and kidney did not form precipitin bands. The antigen was purified from the chrmatin of Novikoff hepatoma cells by exclusion chromatography on Sephadex G-150 and preparative nondenaturing polyacrylamide gel electrophoresis. Its migration on denaturing sodium dodecyl sulfate-polyacrylamide gels corresponded to a molecular weight of 26,000. Amino acid analysis showed that the ratio of acidic to basic amino acids was 1.4 to 1.0. Evidence for its homogeneity included its migration as a single protein spot on two-dimensional polyacrylamide gel electrophoresis and its single lysine amino-terminal amino acid. This protein is a glycoprotein, as shown by the presence of 15 moles of galactosamine per mole of antigen. These studies demonstrate the presence of a fetal glycoprotein in the chromatin of two tumors that may have an important role in determining their gene products.

The modifying effect of autologous serum on leukocyte migration inhibition by liver antigens in systemic lupus erythematosus

The leukocyte migration test was used to examine patients with systemic lupus erythematosus (SLE) for evidence of cell-mediated immunity to human liver microsomes and mitochondria. Testing of both these antigens with leukocytes from patients was carried out simultaneously in culture medium enriched by either 20% fetal bovine serum (the standard test) or substituted 20% autologous serum. Normal controls showed little or no reactivity in the standard test whereas the SLE group revealed a high incidence of significant leukocyte migration inhibition to both antigens which, however, was considerably reduced by the substitution of autologous serum. The results suggest that the sera of patients with SLE contain factor(s) capable of blocking the in vitro expression of cell-mediated immunity to human tissue antigens. These factor(s), if active in vivo, might have a role in controlling some of the auto-immune manfestations of the disease.

Soluble and membrane-bound enzyme-active antigens of rat-liver lysosomes

Secondary lysosomes were isolated from rat liver and separated into a soluble and a membrane fraction. Plasma membranes and microsomes were also isolated and antisera against the various fractions were prepared in rabbits. Lysosomal content and detergent-solubilized membrane fractions were analysed in two-dimensional immunoelectrophoresis (crossed immunoelectrophoresis). The immunoprecipitates were stained by histochemical procedures for different enzyme activities such as phosphatases, non-specific esterase, arylsulphatase, glycosidases and L-leucyl-beta-naphthylamidase. When lysosomal content was tested against its corresponding antiserum, 17 different precipitates could be seen. Most of the enzyme activities tested were shown to reside separately in one or a few precipitates each. In contrast, when the membrane extracts were investigated, a more polymorphic pattern of enzyme-active precipitates appeared. Thus, when lysosomal membrane extracts were reacted with homologous antiserum 11 precipitates with acid phosphatase activity were obtained. Several of the antigens were electrophoretically different and immunologically non-identical. As expected from the biology of secondary lysosomes, many of their antigens were also found in microsomes and/or plasma membranes, but several antigens unique for lysosomes were detected concomitantly. Closer analysis of these results indicated that several seemingly identical enzyme-active proteins occurred both in soluble and membrane-associated forms. However, while many of the membrane antigens expressed 2-4 different enzyme activities, only one activity was detected in individual precipitates of the lysosomal content. Thus, acid phosphatase activity was found together with esterase activity in three membrane-associated antigens. The precipitates formed by two of these also stained for arylsulphatase and nucleoside tri-, di- and monophosphatase activities. L-Leucyl-beta-naphthylamidase activity was found in one additional acid-phosphatase-active precipitate.

Hepatic disorders associated with liver-kidney microsomal antibodies

A study of the clinical associations of a recently defined tissue autoantibody, the liver/kidney microsomal (L.K.M.) antibody, showed that out of 33 patients 26 had clinical liver disease. Fifteen of the patients had active chronic hepatitis and there were seven cases of acute hepatitis, precipitated by presumed virus A infection in three instances and by drug hypersensitivity in the other four. The remaining cases with liver disease included two with subclinical hepatitis and two with hepatocellular carcinoma. Evidence is presented that the patients with active chronic hepatitis may represent a distinct subgroup of the disease with a young mean age, an even male to female ratio, and a striking lack of other nonorgan-specific autoantibodies-that is, antinuclear and smooth muscle-which are usually present in the other autoimmune variant of the disease.

Characterization of the microsomal antigen related to a subclass of active chronic hepatitis

The liver—kidney microsomal (LKM) antigen related to a subgroup of patients with active chronic hepatitis was studied biochemically and by immuno-electronmicroscopy, using peroxidase-conjugated antibodies. The antigenic determinant appears to be on a lipoprotein membrane since it required both phospholipid and protein for antigenic integrity and could not be solubilized.

Complement fixation and absorption of immunofluorescence with microsomal subfractions pointed to localization in both rough and smooth endoplasmic reticulum (ER). Immunoelectronmicroscopy on liver and kidney sections showed an association of the antigen with ribosomes and membranes in rough ER; granular staining was also seen between cisternae. Smooth membranes could not be preserved sufficiently to be recognized. The antigen is independent of ribosomal RNA.

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

The induction of acute hepatocellular necrosis in rats resulted in the production of complement fixing, IgM autoantibodies directed toward inner and outer mitochondrial membranes, microsomal membrane, lysosomal membrane, nuclear membrane, cytosol, but not to plasma membrane. Utilizing selective absorption procedures it was demonstrated that each subcellular membrane fraction possessed unique autoantigenic activity with little or no cross-reactivity between the various membrane fractions. It is proposed that the development of membrane-specific autoantibodies may provide an immunological marker useful in the differential characterization of various subcellular membranes.

Microsomal antibodies in active chronic hepatitis and other disorders

An autoantibody reacting with microsomal membranes has been characterized by a distinctive immunofluorescence pattern on proximal renal tubules and hepatocytes. The microsomal nature of the antigen was demonstrated by absorption and quantitative complement fixation studies. These results showed the antibodies to be quite distinct from the mitochondrial antibodies found in primary biliary cirrhosis.

Microsomal antibodies have so far been detected in sixteen cases, of whom twelve had liver disorders. These antibodies, although rare, may provide a serological marker for a small proportion of active chronic hepatitis cases differing in several respects from other recognized subgroups in this disease.

The effect of microsomal enzyme inhibition on the immunosuppressive and toxic effects of cyclophosphamide

Cyclophosphamide is activated in vivo to toxic alkylating materials by hepatic microsomal enzymes. In mice and rats, inhibition of these enzymes by chloramphenicol or SKF 525A reduces the toxicity of cyclophosphamide but has less effect in rats and no effect in mice on its immunosuppressive activity, so increasing its therapeutic effectiveness.

In contrast, vitamin A alcohol increases cyclophosphamide toxicity, again without affecting its immunosuppressive activity.

Hepatic activation of cyclophosphamide results in the sequential appearance of several metabolites of varying toxicity. Retardation of activation by microsomal enzyme inhibitors may alter the proportions of the various metabolites present and so lead to the differential effects observed here.

Alternatively, exposure of cells to lower concentrations of active products for longer times would favour survival of cells with substantial ability to repair alkylation damage to DNA but not that of cells with little repair ability. The shape of the dose-response curve for cyclophosphamide acting on immunocytes suggests that their repair abilities are limited. The cells essential for survival, which are differentially protected against cyclophosphamide by administering microsomal enzyme inhibitors, are probably not haemopoietic stem cells but may be intestinal epithelial cells.

The clinical relevance of these experiments is discussed.