PubMed Health⌕ Search

Biomedical subjects

J Sjöquist

Publications and source records attributed to J Sjöquist.

At least 55 records · Page 3Linked to original sources
PubMed1982

Isolation of tryptic fragments of human C4 expressing Chido and Rodgers antigens.

It has been shown previously that methylamine is incorporated into the alpha-chain of human C4, resulting in a loss of haemolytic function and the appearance of a free thiol group in the molecule. In the present study it was demonstrated that a fragment resembling C4d is liberated from C4 by trypsin. The fragment--Try-C4d--contains both the methylamine binding site and the free thiol group. When separated on DEAE-Sepharose, four types of Try-C4d, differing in charge and size, could be defined. The size difference was found to parallel the presence of Chido and Rodgers blood group antigens. Fragments of Mr 30,000 carried the Rodgers antigen and the Chido antigen was expressed on fragments of Mr 28,000.

Amino Acid Sequence↗
PubMed1982

The effect of C4 on C1 binding and activation.

Cell-bound human C4 enhances the uptake of C1 by immunoglobulin-carrying cells. The effect is more pronounced with small amounts of IgG than with large amounts. Furthermore, the presence of C4 on the cell surface dramatically promotes the enzymatic effect of C1 on C2. The C1 binding is efficiently blocked, and the C1 activation is almost abolished by pretreating IgG-bearing cells with protein A from Staphylococcus aureus. In contrast, protein A has no effect on cells carrying C4 in addition to IgG. Protein A added in small amounts to IgG-coated sheep erythrocytes inhibits the haemolysis by subsequently added human serum, whereas even larger amounts of protein A has no effect when added to cells carrying C4 as well. Cells with and without C4 take up protein A equally well.

Animals↗
PubMed1982

Polyacrylamide microbeads with entrapped protein A from S. aureus for cell separation.

A technique was developed for the identification and separation of cells according to their surface antigenic markers, based on immobilization of protein A by entrapment in polyacrylamide microbeads. This method is further development of the previous techniques with SpA-containing S. aureus bacteria, but has the advantage of having less unspecific binding to the cells. We show that this technique might be a useful tool for the separation of cells, exemplified by separation of cells on Petri dishes coated with a monolayer of SpA-microbeads. The viability of separated cells was unaffected and adherent cells were easily removed by trypsin.

Acrylic Resins↗
PubMed1981

M antigens of group A streptococci isolated by means of immunochromatography. Biochemical and serological properties.

M proteins of Streptococcus pyogenes types 1 and 12 were purified by immunochromatography on immobilized type-specific opsonizing antibodies. The M proteins were characterized serologically and biochemically. They absorb after immobilization opsonizing antibodies and only precipitate with homologous antisera in immunodiffusion. In SDS PAGE they show one main band, corresponding to mol. weights of 5 X 104 (type 1) and 5.4 X 104 (type 12), accompanied by faint lines, which form with the main band a precipitation line of identity in SDS-crossed immunoelectrophoresis. Both M proteins aggregate blood platelets and clot fibrinogen.

Absorption↗
PubMed1981

Interaction between the labile binding site of human C4 and methylamine.

Human complement component C4 was irreversibly inactivated by low concentrations of methylamine at slightly alkaline pH. The inactivated C4 molecules lost the ability to bind to EAC1 cells but retained th capacity to participate in the formation of classical pathway C3 convertase in the fluid phase. 14C-methylamine was incorporated into the alpha-chain at a ratio of 1 mol methylamine per mol C4.

Complement C4↗
PubMed1981

Further characterization of the alternative protein-A interaction of immunoglobulins: demonstration of an Fc-binding fragment of protein A expressing the alternative reactivity.

Intact IgG and fragments F(ab')2 gamma, Fab gamma and Fc gamma from a rabbit anti-protein-A serum (RapA) and corresponding preparations from normal rabbit IgG (NRG) were tested for their inhibitory effect on the binding of protein-A-reactive 125I-IgE and 125I-Fc gamma, respectively, to protein-A-Sepharose. Intact IgG, F(ab')2 gamma and Fab gamma of RapA inhibited the binding of protein-A-reactive 125I-IgE, whereas only intact IgG and Fc gamma fragments from both RapA and NRG inhibited the binding of 125I-Fc gamma to protein A-Sepharose. Further, the functional relationship between RapA and human polyclonal IgG was studied in a nephelometric test system. Intact IgG or fragments of IgG from human polyclonal IgG and rabbit antiprotein-A were found to affect the precipitation between human IgG and protein A in a similar way. Thus F(ab')2 gamma fragments and intact IgG enhanced the precipitation, whereas Fab gamma and Fc gamma fragments inhibited the precipitation. Protein A and an Fc-binding fragment of protein A (fragment B) were tested for their abilities to link different radiolabelled immunoglobulin preparations expressing the alternative and the classical protein-A reactivity to immobilized Fc fragments. All proteins expressing the alternative reactivity were efficiently bound both by fragment B and by protein A, indicating that fragment B, in addition to its classical Fc-binding activity, also expresses the alternative protein-A reactivity.

Animals↗
PubMed1981

Quantitation of specific IgG antibodies in rabbits by a solid-phase radioimmunoassay with 125I-protein A from Staphylococcus aureus.

Radioiodinated protein A (SpA) from Staphylococcus aureus was used to quantitate specific antibodies of the IgG class at the nanogram level in rabbit serum by a standardized radioimmunoassay with the antigen covalently bound to paper discs. Quantitation of IgG in micrograms of IgG per millilitre of serum was done by using a standard curve with purified anti-bovine serum albumin (BSA) IgG or by means of the calculated molar SpA to rabbit IgG ratio of 1:1, thus converting counts per minute of 125I-SpA to nanograms of IgG. The molar ratio for SpA to human IgG was also 1:1. The unspecific binding of IgG to the paper discs was studied and could be depressed by hen serum or by adsorption of the serum sample to cellulose before the assay. The affinity constants of the extracellular SpA and human, rabbit and guinea-pig IgG, respectively, were determined and found to be close to the values previously calculated for cell-wall-bound SpA. The applicability of the assay was demonstrated by quantitation of the specific IgG response on different days after immunization of rabbits with BSA and 3,4-dinitrobenzene (DNP)-BSA.

Animals↗
PubMed1981

Isolation of component C4 of human complement and its polypeptide chains.

Component C4 of human complement was purified from fresh frozen plasma with a yield of 25% using an initial batch separation with quaternary diethyl-(2-hydroxypropyl)aminoethyl--Sephadex followed by column chromatography on DEAE-cellulose and gel filtration in Sephadex G-200. The final product was homogenous according to polyacrylamide gel electrophoresis and immunochemical methods. Low-speed sedimentation-equilibrium analyses revealed a molecular weight of 189,000, using a value of 0.736 ml/g for the partial specific volume. The polypeptide chains of reduced and alkylated C4 were separated on DEAE-Sepharose in the presence of 8 M urea. Gel filtration in Sepharose 4B in 6 M guanidine hydrochloride revealed molecular weights of 88,000, 72,000 and 32,000 for the alpha, beta and gamma chain respectively. The amino acid compositions of component C4 and its constitutive chains were also determined.

Amino Acids↗
PubMed1980

Staphylococcus aureus and protein A as mitogens for rabbit T lymphocytes.

The thymidine uptake by rabbit lymph nodes, spleen and peripheral blood lymphocytes was stimulated by Protein A (SpA) and SpA-containing staphylococci. The cell fraction enriched in T lymphocytes showed a higher degree of stimulation with SpA than the fraction enriched in B cells. Rabbit thymocytes showed a marked thymidine uptake by treatment with SpA but not with staphylococci. The monovalent fragment B of SpA (reacting with IgG) neither stimulated nor inhibited the incorporation of thymidine in rabbit lymph node lymphocytes indicating that the Fc reacting site of SpA cannot be responsible for the mitogenicity.

Animals↗
PubMed1979

IgG-binding sites on macrophage cell membrane. I. Identification of two distinct Fc receptors on mouse peritoneal macrophages.

Evidence is presented concerning the existence on mouse peritoneal macrophages of two separate and distinct Fc receptors, one for cytophilic monomeric IgG (mIgG) and the other for polymeric IgG. The latter Fc receptor recognizes both heat-aggregated IgG and antigen-complexed IgG. The major findings of our studies are: (a) the different susceptibility of the two Fc receptor types by pronase, trypsin or phospholipase C; (b) the independent modulation of these two binding sites on the cell membrane; (c) the inability of mIgG to inhibit the binding of particulate antigen-complexed IgG ligand; (d) the ability of mIgG molecules which are devoid of the cytophilic property to attach to the macrophage surface upon their polymerization induced by heating or antigen. The results are discussed in terms of "cytophilic" and "opsonic" Fc receptor types which may provide different functional abilities for normal macrophages.

Animals↗
PubMed1979

IgG-binding sites on macrophage cell membrane. II. Mobility of Fc receptors induced by the interaction with their corresponding IgG ligands.

Mouse peritoneal macrophages were charged with IgG molecules in monomeric (mIgG), heat-aggregated (agIgG) or antigen-complexed (acIgG) form. Upon exposure to 37 degrees C, all bound IgG ligand types are redistributed on the cell surface due to the mobilization of their corresponding Fc receptor (FcR). The major findings regarding the fate of FcR on macrophages bearing IgG ligands are as follows: (a) the FcR involved in the binding of cytophilic molecules has a slow movement on the cell membrane and forms patches but never caps, while the opsonic type of FcR is rapidly capped; (b) the mobility of IgG-binding sites was temperature-dependent and was affected differently by sodium azide; this metabolic inhibitor enhances the disappearance of mIgG from the cell surface but decreases the capping and the disappearance of polymeric ligands; (c) both FcR types are probably ingested when complexed with specific ligand, and consequently, the rebinding of homologous IgG molecules is reduced, the clearing induced by agIgG or acIgG binding being much more extensive; and (d) cells cleared of their opsonic types of FcR are able to regenerate the receptor molecules with 8 h of incubation at 37 degrees C.

Animals↗
PubMed1979

Red cell-linked antibody assay for detection of antigenic markers on cell surfaces.

A direct method for demonstrating antigenic markers on cell surface has been developed which makes use of the ability of bovine red blood cells coated with protein A of Staphylococcus aureus (ES) to binding IgG antibody without agglutinating. Red cell-linked rabbit IgG antibody reagents (ESA) were prepared in this way, and Ig-, IgM- and Thy-1-bearing mouse spleen and peripheral blood lymphocytes were identified by a rosette assay.

Animals↗
PubMed1979

Physico- and immunochemical properties of staphylococcal protein A extracellularly produced by a set of mutants from Staphylococcus aureus Cowan I.

Mutant strains of Staphylococcus aureus have been isloated using a simple cosedimentation technique. While the parental strain contains predominantly a cell-bound protein A, the mutant strains exclusively produce extracellular protein A. The mutant forms of protein A all have lower molecular weights than that of protein A from the parental strain. They showed the same antigenicity as the parental protein A and gave similar reactivity with immunoglobulin to the parental one except for one mutant. A conspicuous spur was observed between the parental protein A and that produced by the mutant against normal dog serum in the micro-Ouchterlony immunodiffusion test.

Amino Acids↗