Reducing SDS-polyacrylamide Gel Electrophoresis Research Articles

Preparation and radiolabeling of a lyophilized (kit) formulation of DOTA-rituximab with ⁹⁰Y and ¹¹¹In for domestic radioimmunotherapy and radioscintigraphy of non-Hodgkin's lymphoma.

BackgroundOn the basis of results of our previous investigations on 90Y-DTPA-rituximab and in order to fulfil national demands to radioimmunoconjugates for radioscintigraphy and radioimmunotherapy of Non-Hodgkin’s Lymphoma (NHL), preparation and radiolabeling of a lyophilized formulation (kit) of DOTA-rituximab with 111In and 90Y was investigated.Methods111In and 90Y with high radiochemical and radionuclide purity were prepared by 112Cd (p,2n)111In nuclear reaction and a locally developed 90Sr/90Y generator, respectively. DOTA-rituximab immunoconjugates were prepared by the reaction of solutions of p-SCN-Bz-DOTA and rituximab in carbonate buffer (pH = 9.5) and the number of DOTA per molecule of conjugates were determined by transchelation reaction between DOTA and arsenaso yttrium(III) complex. DOTA-rituximab immunoconjugates were labeled with 111In and 90Y and radioimmunoconjugates were checked for radiochemical purity by chromatography methods and for immunoreactivity by cell-binding assay using Raji cell line. The stability of radiolabeled conjugate with the approximate number of 7 DOTA molecules per one rituximab molecule which was prepared in moderate yield and showed moderate immunoreactivity, compared to two other prepared radioimmunoconjugates, was determined at different time intervals and against EDTA and human serum by chromatography methods and reducing SDS-polyacrylamide gel electrophoresis, respectively. The biodistribution of the selected radioimmunoconjugate in rats was determined by measurement of the radioactivity of different organs after sacrificing the animals by ether asphyxiation.ResultsThe radioimmunoconjugate with approximate DOTA/rituximab molar ratio of 7 showed stability after 24 h at room temperature, after 96 h at 4°C, as the lyophilized formulation after six months storage and against EDTA and human serum. This radioimmunoconjugate had a biodistribution profile similar to that of 90Y-ibritumomab, which is approved by FDA for radioimmunotherapy of NHL, and showed low brain and lung uptakes and low yttrium deposition into bone.ConclusionFindings of this study suggest that further investigations may result in a lyophilized (kit) formulation of DOTA-rituximab which could be easily radiolabeled with 90Y and 111In in order to be used for radioimmunotherapy and radioscintigraphy of B-cell lymphoma in Iran.

Mass spectrometry identification of NASP binding partners in HeLa cells

Nuclear autoantigenic sperm protein (NASP) is a linker histone binding protein that is cell-cycle regulated. Synchronized HeLa cells are delayed in progression through the G1/S border when transiently transfected to overexpress full-length NASP, but not the histone-binding site (HBS) deletion mutant (NASP-DeltaHBS). The purpose of the current study was to identify possible NASP-associated proteins in HeLa cell nuclei that could elucidate NASP's influence on the cell cycle and chromatin remodeling. For this purpose, we employed a new approach: mass spectrometry identification of initially cross-linked proteins after their separation in a second dimension by reducing SDS-polyacrylamide gel electrophoresis (SDS-PAGE). Of the twelve proteins identified, three appear to be relevant to NASP's function: heat shock protein 90 (HSP90), DNA-activated protein kinase, and ATP-dependent DNA helicase II (70-kDa subunit). Individual protein-protein interactions were tested by immunoprecipitation techniques. This new method can be used for expedited identification of binding partners of different proteins in enriched fractions and as a complementary or alternative strategy to the yeast two-hybrid system and immunoprecipitation methods.

Cultivar discrimination of Portuguese Lupinus albus by seed protein electrophoresis: the importance of considering “glutelins” and glycoproteins

The Osborne protein fractions of seeds of 17 Lupinus albus cultivars from different regions in Portugal (obtained from plants grown at the same location) were analysed. The objective of this work was to examine the variability in the seed protein fractions of such a L. albus germplasm sample in order to disclose existing genetic relationships and to obtain information useful for a breeding program. Globulins and, interestingly, the fraction extracted with NaOH (“glutelins”) were the major seed protein constituents. The several protein fractions were separated by electrophoresis (reducing SDS polyacrylamide gel electrophoresis) and the patterns examined by multivariate analysis. Bands of “glutelins” together with those of glycosylated polypeptides were found to have the highest discriminating capacity. Lupin populations were grouped according to their clinal geographical distribution from north (small-seeded, higher plant architecture and later flowering type) to south (large-seeded, shorter and early flowering type). It is also possible that polypeptide patterns could reflect microclimatic specificities related with altitude and temperature. In fact, one cultivar from the south but from high altitude was grouped with the north plant types adapted to colder and wetter weather, whereas two cultivars from a warmer north region were grouped with the southern types. The results show, in addition, that a general correlation exists between cultivar early flowering characteristics and higher amounts of both total seed protein and glutelins, and lower glutelin glycosylation. Since high seed protein content and early flowering are important aims of lupin breeding programs, these findings on the seed protein fractions could stimulate and direct future research in lupin improvement.

Expression of α2,8/2,9-Polysialyltransferase fromEscherichia coli K92: CHARACTERIZATION OF THE ENZYME AND ITS REACTION PRODUCTS

The capsular polysaccharide of Escherichia coli K92 contains alternating -8-NeuAcalpha2- and -9-NeuAcalpha2- linkages. The enzyme catalyzing this polymerizing reaction has been cloned from the genomic DNA of E. coli K92. The 1.2-kilobase polymerase chain reaction fragment was subcloned in pRSET vector and the protein was expressed in the BL21(DE3) strain of E. coli with a hexameric histidine at its N-terminal end. The enzyme was isolated in the supernatant after lysis of the cells and fractionated by ultracentrifugation. Western blotting using anti-histidine antibody showed the presence of a band that migrated at about 47.5 kDa on both reducing and nonreducing SDS-polyacrylamide gel electrophoresis, indicating a monomeric enzyme. Among the carbohydrate acceptors tested, N-acetylneuraminic acid and the gangliosides G(D3) and G(Q1b) were preferred substrates. The cell-free enzyme reaction products obtained were characterized by NMR and mass spectrometry, which indicated the presence of both alpha2,9- and alpha2,8-linked polysialyl structure. The K92 neuS gene was used to transform the K1 strain of E. coli, the capsule of which contains only -8-NeuAcalpha2- linkages. Analysis of the polysaccharides isolated from these transformed cells is consistent with the presence of both -8-NeuAcalpha2- and -9-NeuAcalpha2- linkages. Our results suggest that the neuS gene product of E. coli K92 catalyzes the synthesis of polysialic acid with alpha2,9- and alpha2,8-linkages in vitro and in vivo.

The Heparin-binding Domain of Extracellular Superoxide Dismutase Is Proteolytically Processed Intracellularly during Biosynthesis

Extracellular superoxide dismutase (EC-SOD) is the only known extracellular enzyme designed to scavenge the superoxide anion. The purified enzyme exists in two forms when visualized by reduced SDS-polyacrylamide gel electrophoresis: (i) intact EC-SOD (Trp1-Ala222) containing the C-terminal heparin-binding domain and (ii) cleaved EC-SOD (Trp1-Glu209) without the C-terminal heparin-binding domain. The proteolytic event(s) leading to proteolysis at Glu209-Arg210 and removal of the heparin-binding domain are not known, but may represent an important regulatory mechanism. Removal of the heparin-binding domain affects both the affinity of EC-SOD for and its distribution to the extracellular matrix, in which it is secreted. During the purification of human EC-SOD, the intact/cleaved ratio remains constant, suggesting that proteolytic removal of the heparin-binding domain does not occur during purification (Oury, T. D., Crapo, J. D., Valnickova, Z., and Enghild, J. J. (1996) Biochem. J. 317, 51-57). This was supported by the finding that fresh mouse tissue contains both intact and cleaved EC-SOD. To study other possible mechanisms leading to the formation of cleaved EC-SOD, we examined biosynthesis in cultured rat L2 epithelial-like cells using a pulse-chase protocol. The results of these studies suggest that the heparin-binding domain is removed intracellularly just prior to secretion. In addition, the intact/cleaved EC-SOD ratio appears to be tissue-dependent, implying that the intracellular processing event is regulated in a tissue-specific manner. The existence of this intracellular processing pathway may thus represent a novel regulatory pathway for affecting the distribution and effect of EC-SOD.

Comparative Properties of Two Cysteine Proteinases (Gingipains R), the Products of Two Related but Individual Genes ofPorphyromonas gingivalis

Proteolytic enzymes produced by Porphyromonas gingivalis are important virulence factors of this periodontopathogen. Two of these enzymes, referred to as arginine-specific cysteine proteinases (gingipains R), are the product of two related genes. Here, we describe the purification of an enzyme translated from the rgpB/rgp-2 gene (gingipain R2, RGP-2) and secreted as a single chain protein of 422 residues. The enzyme occurs in several isoforms differing in pI, molecular mass, mobility in gelatin zymography gels, and affinity to arginine-Sepharose. In comparison to the 95-kDa gingipain R1, a complex of catalytic and hemagglutinin/adhesin domains, RGP-2 showed five times lower proteolytic activity, although its activity on various P1-arginine p-nitroanilide substrates was generally higher. Gingipains R amidolytic activity, but not general proteolytic activity, was stimulated by glycyl-glycine. However, in cases of limited proteolysis, such as the inactivation of alpha-1-antichymotrypsin, glycyl-glycine potentiated inhibitor cleavage. In contrast, alpha-1-proteinase inhibitor was not inactivated by gingipains R and only underwent proteolytic degradation during boiling in reducing SDS-polyacrylamide gel electrophoresis treatment buffer. Similarly, native type I collagen was completely resistant to cleavage by gingipains but readily degraded after denaturation. Together, these data explain much of the controversy regarding gingipains structure and substrate specificity and indicate that these enzymes function as P. gingivalis virulence factors by proteolysis of selected target proteins rather than random degradation of host connective tissue components.

Construction and Binding Kinetics of a Soluble Granulocyte-Macrophage Colony-stimulating Factor Receptor α-Chain-Fc Fusion Protein

Granulocyte-macrophage colony-stimulating factor (GM-CSF) activity is mediated by a cellular receptor (GM-CSFR) that is comprised of an alpha-chain (GM-CSFRalpha), which specifically binds GM-CSF, and a beta-chain (betac), shared with the interleukin-3 and interleukin-5 receptors. GM-CSFRalpha exists in both a transmembrane (tmGM-CSFRalpha) and a soluble form (sGM-CSFRalpha). We designed an sGM-CSFRalpha-Fc fusion protein to study GM-CSF interactions with the GM-CSFRalpha. The construct was prepared by fusing the coding region of the sGM-CSFRalpha with the CH2-CH3 regions of murine IgG2a. Purified sGM-CSFRalpha-Fc ran as a monomer of 60 kDa on reducing SDS-polyacrylamide gel electrophoresis but formed a trimer of 160-200 kDa under nonreducing conditions. The sGM-CSFRalpha-Fc bound specifically to GM-CSF as demonstrated by standard and competitive immunoassays, as well as by radioligand assay with 125I-GM-CSF. The sGM-CSFRalpha-Fc also inhibited GM-CSF-dependent cell growth and therein is a functional antagonist. Kinetics of sGM-CSFRalpha-Fc binding to GM-CSF were evaluated using an IAsys biosensor (Affinity Sensors, Paramus, NJ) with two assay systems. In the first, the sGM-CSFRalpha-Fc was bound to immobilized staphylococcal protein A on the biosensor surface, and binding kinetics of GM-CSF in solution were determined. This revealed a rapid koff of 2.43 x 10(-2)/s. A second set of experiments was performed with GM-CSF immobilized to the sensor surface and the sGM-CSFRalpha-Fc in solution. The dissociation rate constant (koff) for the sGM-CSFRalpha-Fc trimer from GM-CSF was 1.57 x 10(-3)/s, attributable to the higher avidity of binding in this assay. These data indicate rapid dissociation of GM-CSF from the sGM-CSFRalpha-Fc and suggest that in vivo, sGM-CSFRalpha may need to be present in the local environment of a responsive cell to exert its antagonist activity.

Sodium Dodecyl Sulfate-stable Complexes between Serpins and Active or Inactive Proteinases Contain the Region COOH-terminal to the Reactive Site Loop

Recently inhibitors of the serpin family were shown to form complexes with dichloroisocoumarine (DCI)-inactivated proteinases under native conditions (Enghild, J. J., Valnickova, Z., Thøgersen I., and Pizzo, S. V. (1994) J. Biol. Chem. 269, 20159-20166). This study demonstrates that serpin-DCI/proteinase complexes resist dissociation when analyzed in reduced SDS-polyacrylamide gel electrophoresis. Previously, SDS-stable serpin-proteinase complexes have been observed only between serpins and catalytically active proteinases. The stability of these complexes is believed to result from an acyl-ester bond between the active site Ser195 of the proteinase and the alpha-carbonyl group of the scissile bond in the reactive site loop. We have further analyzed the structure of the SDS-stable serpin-proteinase and serpin-DCI/proteinase complexes. The results of these studies demonstrate the presence of the COOH-terminal region of the serpin in both complexes. Since (i) modification of Ser195 does not prevent formation of SDS-stable complexes and (ii) COOH-terminal peptides are present in both complexes, the previously described mechanism does not sufficiently explain the formation of SDS-stable complexes.

Misfolded human chorionic gonadotropin beta subunits are secreted from transfected Chinese hamster ovary cells.

There are six intramolecular disulfide (S-S) bonds that form during intracellular folding of the human chorionic gonadotropin (hCG)-beta subunit. Site-directed mutagenesis of every pair of Cys residues involved in the formation of each S-S bond was used to examine the roles that S-S bonds play in beta subunit folding and secretion. Tryptic maps of secreted hCG-beta showed that only one S-S bond formed in all S-S bond mutants that failed to fold from the earliest detectable beta folding intermediate, p beta 1, into a second major intermediate, p beta 2 (C34A-C88A, C38A-C57A or C9A-C90A mutants), whereas all 5 remaining S-S bonds formed in mutants when p beta 1-->p beta 2 conversion occurred (C23A-C72A, C93A-C100A, or C26A-C110A mutants). Nonreducing SDS-polyacrylamide gel electrophoresis showed that beta multimers were secreted from cells expressing S-S bond mutations where the folding of p beta 1-->p beta 2 was blocked. However, for mutations where p beta 1-->p beta 2 conversion was efficient, beta monomers rather than multimers were secreted. For all cell lines studied, secreted hCG-beta migrated as monomeric beta during reducing SDS-polyacrylamide gel electrophoresis, indicating that hCG-beta multimers formed via intermolecular cross-linking of unpaired thiols. Tryptic maps of hCG-beta isolated from mutants lacking the 34-88 bond, where > 80% turnover occurs, showed that only the 38-57 S-S bond formed. beta Subunits lacking the 9-90 linkage also have only S-S bond 38-57 formed, but < 10% turnover of C9A-C90A hCG-beta occurs. Thus, subtle conformational differences between partially folded or misfolded beta subunits may determine whether hCG-beta is degraded, or undergoes intracellular translocation and secretion.

Construction and Characterization of Thrombin-resistant Variants of Recombinant Human Protein S

Protein S is a vitamin K-dependent plasma protein that functions as a cofactor of activated protein C (APC) in the inactivation of coagulation factors Va and VIIIa. Protein S, migrates as a doublet on reduced SDS polyacrylamide gel electrophoresis. This heterogeneity in molecular weight has been explained by limited proteolysis of protein S. Human protein S contains at Arg-49, Arg-60 and Arg-70 three potential cleavage sites. Whether cleavage occurs at all three sites is not known. To study the role of these arginine residues in human protein S, we have replaced them by leucine or isoleucine. All seven possible variants were constructed: three variants with single mutations (R49L, R60L, R70I), three variants with double mutations (R49L/R60L, R60L/R70I, R49L/R70I) and one variant with a triple mutation (R49L/R60L/R70I). On reduced SDS polyacrylamide gels the single and double variants migrate as a doublet just like the wild type protein S. The triple variant migrates as a single band at a molecular weight corresponding to the upper band of the doublet. The upper band of the single and double variants but not of the triple variant could be converted into the lower band by thrombin treatment. All variants showed cofactor activity to APC in a clotting assay. After thrombin treatment, this cofactor activity was abolished for the single (R49L, R60L, R70I) and double variants (R49L/R60L, R60L/R70I, R49L/R70I), while the triple variant (R49L/R60L/R70I) tested at several concentrations, retained its cofactor activity completely, suggesting resistance to thrombin. This shows that thrombin can cleave at all three arginine sites and that cleavage at each of these sites results in the loss of APC cofactor activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Purification of a cathepsin L-like proteinase secreted by adult Fasciola hepatica

A cysteine proteinase released in vitro by Fasciola hepatica was purified to homogeneity by Sephacryl S-200 gel filtration chromatography followed by QAE-Sephadex chromatography. The purified enzyme resolves as a single band with an apparent molecular size of 27 kDa on reducing SDS-polyacrylamide gel electrophoresis; however, under non-reducing conditions it migrates as multiple bands, each with enzymatic activity, in the apparent molecular size range 60–90 kDa. The sequence of the first 20 N-terminal amino acids of the enzyme shows considerable homology with cathepsin L-like proteinases. Immunolocalisation studies revealed that the cathepsin L-like proteinase is concentrated within vesicles in the gut epithelial cells of liver fluke.

Characterization of a peroxidase in excretory-secretory product of adult Paragonimus westermani.

When activity of peroxidase in adult Paragonimus westermani was monitored using o-dianisidine and H2O2 as substrates, its specific activity was 1.5 times higher in excretory-secretory product (ESP) than in crude extract. The enzyme was purified by two purification steps of Sephacryl S-300 Superfine gel permeation and DEAE-Trisacryl M anion exchange chromatographies. Its activity increased 16.9 fold with 32.3% recovery. The enzyme was inhibited totally by 1 millimoles of dithiothreitol (DTT), 2-mercaptoethanol and azide. Molecular mass was 16 kDa in reducing SDS-polyacrylamide gel electrophoresis (PAGE) or 19 kDa in TSK-Blue gel filtration high performance liquid chromatography (HPLC), respectively. Special staining for peroxidase by diaminobenzidine on SDS-PAGE confirmed the activity. The peroxidase was less reactive to a paragonimiasis serum when observed by SDS-PAGE/immunoblot. In addition, specific activities of superoxide dismutase (SOD) and catalase were also identified in the ESP. High activities of these antioxidant enzymes in ESP indicate that they are parts of defense mechanisms against reactive oxygen intermediates from host.

A simple and rapid method to study the association of the contact proteins of blood coagulation

Native and reduced SDS polyacrylamide gel electrophoresis on the automated PhastSystem (Pharmacia) were used to demonstrate protein-protein binding interactions and structural changes during proteolytic activations of the proteins involved in contact activation. The “mobility shift” assay in native gels has been used to visualize the kinetics of activation of factor XII by dextran sulfate as well as the formation of kallikrein-cleaved high molecular weight kininogen. It shows the formation of prekallikrein-high molecular weight kininogen complexes and factor XII-dextran sulfate complex for the first time in gels. The use of automation makes this procedure fast and reproducible using nanogram amounts of protein in relatively short time.

Characterization and localization of nitric oxide synthase in non-adrenergic non-cholinergic nerves from bovine retractor penis muscles.

1. Partially purified soluble nitric oxide (NO) synthase was isolated from the bovine retractor penis muscle (BRP), a tissue in which the inhibitory response to non-adrenergic non-cholinergic nerve (NANC) stimulation appears to be mediated by NO or NO-like material. 2. NO synthase from BRP used L-arginine as a substrate, required NADPH, tetrahydrobiopterin, and FAD as co-factors and was Ca2+/calmodulin-dependent. The activity of NO synthase was inhibited by NG-methyl-L-arginine and NG-nitro-L-arginine, and haemoglobin blocked the effect of NO formed by the enzyme. 3. On reducing SDS polyacrylamide gel electrophoresis the apparent molecular mass of NO synthase from BRP was 160 +/- 2 kDa, which is similar to that of the cerebellar NO synthase. Protein immunoblot and immunoprecipitation showed that NO synthase from BRP cross-reacted with the selective antiserum to neuronal NO synthase from rat cerebellum. 4. Immunohistochemistry using the same antiserum demonstrated that NO synthase in BRP was located exclusively within nerve fibres. Thus, autonomic nerves synthesizing the NANC neurotransmitter seem to contain an isoform of NO synthase which is similar to that from rat cerebellum.

Differential expression of laminin chains in hepatic lipocytes

The lipocyte is an important source of laminin in the normal liver. We have investigated the expression of the 3 chains of laminin in isolated rat lipocytes. Both B 1 and B 2 chains, but not A, were found in medium from 5-day-old lipocyte primary cultures by immunoblotting and immunoprecipitation of 35S-labeled proteins after reducing SDS-polyacrylamide gel electrophoresis. An additional polypeptide of M r=380 000 was identified by immunoprecipitation. Under non-reducing conditions only one M r=900 000 band was revealed. High levels of B 1 and B 2 mRNAs were also demonstrated in 5-day-old cultured lipocytes while at the time of seeding, only B 2 chain mRNAs were clearly detectable. A chain mRNA was constantly absent. These results suggest that lipocytes produce a variant form of laminin in primary culture and that the M r=380 000 polypeptide could be unrelated to the A chain of laminin.

Purification and characterization of a Cu, Zn-superoxide dismutase from adult Paragonimus westermani

In cytosolic fraction of adult Paragonimus westermani, superoxide dismutase activity was identified (4.3 units/mg of specific activity) using a xanthine-xanthine oxidase system. The enzyme was purified 150 fold in its activity using the ammonium sulfate precipitation, DEAE-Trisacryl M anion-exchange chromatography and Sephadex G-100 molecular sieve chromatography. The enzyme exhibited the enhanced activity at pH 10.0. The enzyme activity totally disappeared in 1.0mM cyanide while it remained 77.8% even in 10 mM azide. These findings indicated that the enzyme was Cu, Zn-SOD type. Molecular mass of the enzyme was estimated to be 34 kDa by gel filtration and 17 kDa on reducing SDS-polyacrylamide gel electrophoresis which indicated a dimer protein.

Post-translational changes in tertiary and quaternary structure of the insulin proreceptor. Correlation with acquisition of function.

Tertiary and quaternary structural changes that occur during post-translational processing of the insulin proreceptor were examined in 3T3-L1 adipocytes. In pulse-chase experiments with [35S]methionine, labeled insulin receptor species, isolated by immuno- and insulin-affinity adsorption, were analyzed by sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis under conditions where intra- and intermolecular disulfide bonds remained intact or were cleaved by reduction. Reducing SDS-polyacrylamide gel electrophoresis confirmed that the insulin receptor is synthesized as a long-lived (t1/2 = 3 h) proreceptor precursor of 210 kDa which undergoes proteolytic cleavage and carbohydrate maturation to form the alpha- and beta-subunits of the mature receptor. The proreceptor acquires insulin binding activity through a subtle structural change (t1/2 = 45 min) detected only by an autoimmune antibody specific for an epitope of the active insulin binding site. Analysis of insulin receptor species by nonreducing SDS-polyacrylamide gel electrophoresis revealed that the proreceptor undergoes two additional structural changes not detected by reducing SDS-polyacrylamide gel electrophoresis. The proreceptor is synthesized as a monomer (M1) with an apparent molecular mass of 170 kDa that is converted by disulfide rearrangement to another monomeric form of 190-kDa apparent molecular mass (M2). N-Linked glycosylation is required for this transition, since aglycoproreceptor, synthesized in the presence of tunicamycin, does not undergo any detectable tertiary or quaternary structural changes. M2 self-associates to form a disulfide-linked proreceptor dimer (D) which is subsequently proteolytically processed, forming the mature, disulfide-linked alpha 2 beta 2 receptor tetramer. The mature receptor was distinguished from the three proreceptor species (M1, M2, and D) by its cell surface location and its ability to bind tightly to wheat germ agglutinin-agarose, indicating the presence of complex oligosaccharide chains. Subcellular fractionation indicated that both the M1 to M2 and M2 to D conversions occur in the endoplasmic reticulum. Separation of the nonreduced proreceptor species into "active" and "inactive" forms by affinity chromatography on insulin-agarose revealed that neither the transition of M1 to M2, nor of M2 to D, is correlated with the acquisition of insulin binding function. Rather, during its life-time, the M2 species acquires insulin binding activity and an epitope recognized by a binding site specific autoimmune antibody through a subtle structural change not detected by reducing or nonreducing SDS-polyacrylamide gel electrophoresis.

'Attached cell' antigen 28.3.7 mapping to human chromosome 15 characterises TPA-induced differentiation of the promyelocytic HL-60 cell line to give macrophage/monocyte populations.

Human cells growing in vitro attached to the substratum express a cell antigen called 28.3.7 identified by a species-specific monoclonal antibody. This antigen is not expressed on human cells growing in suspension. The antigen has a mol. wt. in reduced SDS-polyacrylamide gel electrophoresis gels of 95 000 and in human-mouse somatic cell hybrids, expression of the antigen is controlled by a gene, MIC7, mapping to human chromosome 15. The antigen functions as a marker for macrophage differentiation. In vitro differentiation of the 28.3.7 antigen-negative human promyelocytic leukaemia line HL-60 induced by phorbol ester, results in the formation of a macrophage/monocyte population and the concomitant expression of the 28.3.7 antigen on this adherent cell population.

Albumin-immunoglobulin complexes in human serum: classification and immunochemical analysis.

A complex between serum albumin and immunoglobulins was observed on immunoelectrophoresis in six patients. Two patients with multiple myeloma had monoclonal IgA-albumin complexes; one of these complexes was formed by covalent bonds and the other by non-covalent bonds. Four patients displayed non-covalent IgG-albumin complexes: of these, one had multiple myeloma, two had been treated with nitrofurantoin for prolonged periods, and one had diabetes mellitus. The IgG-albumin complex of the last patient was subjected to a detailed immunochemical analysis. The albumin-specific antibodies were isolated by affinity chromatography and analysed, using a sensitive tritium labelling technique. The antibodies were polyclonal, complexed with serum albumin through their Fab portion, and showed a high specificity for the human albumin as compared with bovine and rabbit albumins. The serum albumin of two patients displayed an abnormal behaviour in reduced SDS-polyacrylamide gel electrophoresis (PAGE). The abnormal albumins had an apparent molecular weight of 52,000 and could react with rabbit anti-human serum albumin like the normal protein. No abnormal albumin could be detected in 20 other patients' sera, including nitrofurantoin-treated patients and normal controls. These findings suggest a possible role for an altered self-component in the triggering of a specific autoimmune reaction.