Håkan Nygren

A solid-phase enzyme-linked immunospot (ELISPOT) assay for enumeration of specific antibody-secreting cells

A solid-phase enzyme-linked immunosorbent assay (ELISPOT) is described for enumeration of cells secreting specific antibody. Spleen cells from immunized mice are incubated in antigen-coated polystyrene plates. After removal of the cells, bound antibodies are demonstrated by means of an immunoenzyme procedure in which enzyme-substrate reactions are performed in agarose. Dark-brown circular zones (spots), localized in areas of the dish where antibody production has occurred, are enumerated with the naked eye. Spectrophotometric estimation of enzyme-bound activity may be performed by substituting the gel for a liquid buffer, allowing accurate estimation of the total amount of secreted antibody. Versatile, sensitive and very easy to perform, this new assay provides a useful alternative to conventional plaque-forming cell assays.

Kinetics of antigen-antibody reactions at solid-liquid interfaces

The kinetics of antigen-antibody reactions is reviewed with special attention paid to the specific properties at solid-liquid interfaces. Theories of possible diffusion limitation in forward reaction rates are compared to experiments. It is found that the intrinsic forward reaction rate in the bimolecular antigen-antibody reaction is normally not limited by diffusion either in solution or at the solid-liquid interface. However, reactions at the solid-liquid interface can be diffusion limited due to depletion of reactants close to the surface. This effect depends on geometry, intrinsic reaction rate and surface concentration of receptor molecules. Normally cell surface reactions are not diffusion limited whereas reactions at artificial surfaces often are limited by diffusion. When not limited by diffusion it is also found that the intrinsic forward and reverse reaction rates are lower for surface reactions compared to reactions in solution. Antigen-antibody reactions at solid-liquid interfaces can often be considered as practically irreversible and limited by mass transport or steric interactions.

External diffusion in solid-phase immunoassays

Calculations are presented describing the influence of external diffusion in the kinetics of solid-phase immunoassays. The analysis is concerned with systems where one reactant is immobilized at the surface of a sphere of arbitrary radius. The solution for a plane surface is found as a limiting case. The factors determining whether the reaction is diffusion or reaction controlled are found to be sphere radius, surface concentration of binding sites, forward reaction rate and diffusion constant of reacting species. Means of determining whether the reaction is diffusion or reaction controlled from observable quantities are described. When applied to heterogeneous antibody-antigen binding it is found that normally the binding to cell-size spheres is not limited by external diffusion. However, when applied to solid-phase assays with high surface concentrations of binding sites immobilized at plane surfaces or macroscopic spheres the binding is found to be diffusion limited. The importance of a mass transfer analysis in this case is also discussed.

The initial reactions of TiO2 with blood

The natural titanium oxide (TiO2) layer of commercial sheet titanium was dissolved in hydrofluoric acid. A new oxide layer was grown by oxidation in nitric acid or by annealing at 700 degrees C in air. At this temperature, reaction with nitrogen is unlikely. The purity of the oxidized sheet-titanium surfaces was investigated by Auger spectroscopy. The composition of both surfaces was TiO2 with carbon impurities. The carbon content of the acid-oxidized titanium was 20 +/- 2%, and the carbon content of the heat-oxidized titanium was 14 +/- 2% The initial reactions of the TiO2 surfaces with blood were investigated by short-time exposure to capillary blood and by detection of surface-adsorbed plasma proteins and cells with immunofluorescence. Antibodies specific to fibrinogen, complement factor C1q, prothrombin/thrombin, and platelet membrane antigen were used, and the fluorescence was quantitated by computer-aided image analysis. The results show that serine proteases are the dominating proteins adsorbed onto annealed titanium (C1q = 67 +/- 4.6; pt/t = 97 +/- 0.2; fib = 47 +/- 0.2). The adsorption of serine proteases was lower and the amount of fibrinogen was higher on the acid-oxidized surface (C1q = 46.3 +/- 2.6; pt/t = 25 +/- 2.9; fib = 64 +/- 0.7). Platelets adhered and spread on the annealed titanium surface within 5 sec of blood-material contact. The number of adhering platelets was higher on the acid-oxidized surface.

Kinetics of antibody-binding to surface-immobilized antigen: Influence of mass transport on the enzyme-linked immunosorbent assay (ELISA)

Abstract The kinetics of antibody-binding to surface-immobilized antigen was studied by ellipsometry, using bovine serum albumin as antigen. The results show that the initial binding of antibody was linear to the square root of time rather than time, indicating an initial diffusion-rate limitation of the reaction. The antibody-binding rate was retarded at a surface concentration of 0.2 μg/cm2 and became reaction-rate limited above this surface concentration. The reverse reaction was shown to be too slow to be measured after 43 h dissociation. A Scatchard plot of the data showed time dependence which gave a further indication that the antibody-binding was not an equilibrium reaction. The results obtained from ellipsometry experiments were applied to experiments with the enzyme linked immunosorbent assay (ELISA) which by the sensitive detection system measures the initial antibody-binding to immobilized antigen. It was shown that the dose-response curve of the ELISA could be explained assuming a diffusion-rate limited, irreversible antibody-binding to the immobilized antigen.

Platelet binding and protein adsorption to titanium and gold after short time exposure to heparinized plasma and whole blood

Protein adsorption from human plasma and platelet binding and activation were studied at short blood-titanium/gold contact times. The protein adsorption was studied by ellipsometry-antibody techniques in situ, and adhering platelets were visualized with fluorescein isothiocyanate-labelled anti-CD 61 antibodies. Adhering platelets were quantified by counting labelled cells in microscopic image fields. The spreading of platelets was studied by scanning electron microscopy. The results show that after 1 min of plasma exposure, fibrinogen, IgG and albumin were detectable with antibodies on both surfaces. The amount of deposited fibrinogen and complement decreased with time on titanium, and the amount of adsorbed anti-high molecular weight kininogen increased. No complement was detected on gold surfaces after plasma incubation, and the antibody binding pattern also remained unchanged after prolonged plasma exposure. The surface-bound platelets were found to spread on the gold but not on titanium surfaces. C1q has been shown to induce the expression of P-selectin, i.e. cause secretion reactions in platelets. In this study secreted platelet-microvesicles were found on gold, but not on the titanium surfaces that bound significant amounts of C1q. Thus, the results of the present study indicate that the mixture of fibrinogen, C1q and kininogens, whilst causing adhesion and aggregation, does not result in the activation and microvesicle secretion of platelets. Platelet activation on biomaterial surfaces thus seems to be governed by the mixture of proteins present on that surface, and no one particular protein need cause a known reaction in platelets as obtained when platelets are exposed only to that particular protein.

Reverse enzyme-linked immunospot assay (RELISPOT) for the detection of cells secreting immunoreactive substances

A reverse modification of the recently described enzyme-linked immunospot assay (ELISPOT), based on localized enzyme-substrate reactions in gel, is described for the enumeration of antigen-secreting cells using petri dishes coated with specific antibodies. As a model the detection of mouse and human immunoglobulin-secreting cells has been evaluated. Simple and sensitive, this new method, termed RELISPOT, can be adapted for the quantitation of secreted antigen thus providing additional information on the metabolic state of the population of cells tested.

Adhesion and activation of platelets and polymorphonuclear granulocyte cells at TiO2 surfaces

The initial reactions of two TiO2 surfaces with blood were investigated by short-time exposure to capillary blood and analysis of surface-adsorbed plasma proteins and surface-adhering cells by using immunofluorescence techniques. Antibodies directed against platelet membrane antigen and P-selectin were used to visualize platelet adhesion and activation. Acridine orange and anti-CD11b were used to detect adhesion and activation of polymorphonuclear granulocytes (PMNs). Antibodies against thrombospondin were used as markers for platelet alpha-granules. The fluorescence intensity was quantitated by computer-aided image analysis. Commercially pure, polished sheet titanium was oxidized in two different ways: (1) the natural oxide was dissolved with hydrofluoric acid and a new oxide layer was grown by oxidation in nitric acid, or (2) annealing was performed at 700 degrees C in air. Auger electron spectroscopy and x-ray photoelectron spectroscopy showed that both surfaces had similar composition consisting of TiO2 covered by a carbonaceous surface contamination layer. The thickness of the oxide layer was 4 nm on the acid-oxidized surface and 39 nm on the annealed surface. Optical profilometry and scanning electron microscopy showed that the acid-oxidized surface was rough and the annealed surface was smooth. The fibrinogen/prothrombin-thrombin ratio in the initial protein film differed between the surfaces. The number of adhering platelets was larger at the surface with a high surface concentration of adsorbed fibrinogen. Platelet activation (CD62) and priming of PMNs (CD 11b) were also significantly higher on the acid-oxidized surface. The results indicate that non-self recognition of biomaterials is an array of transient reactions comprising protein-material, protein-cell, and cell-cell interactions.

A receptor-ligand reaction studied by a novel analytical tool—The Isoscope ellipsometer☆

Abstract A receptor-ligand binding reaction, cholera toxin-ganglioside GM 1 , was studied by diffusion of the ligand over a receptor-coated surface. The surface reaction was analyzed by the use of a novel analytical tool, the Isoscope ellipsometer. The thickness profile of the receptor-ligand binding reaction can be directly visualized and photographed with this instrument. Experimental thickness profiles were compared to different theoretically calculated thickness profiles assuming different kinetics of the receptor-ligand reaction. Experimental data were best fitted to theoretical calculations assuming an irreversible and diffusion rate-limited surface reaction. The use of the Isoscope ellipsometer for further studies on receptor-ligand reactions is discussed.

Diffusion in gel-enzyme linked immunosorbent assay (DIG-ELISA): A simple method for quantitation of class-specific antibodies

A new method for quantifying class-specific antibodies is presented. The method has been named Diffusion-In-Gel-Enzyme-Linked-ImmunoSorbentAssay (DIG-ELISA), and is briefly as follows. Antiserum ia allowed to diffuse from wells in a gel layered over an antigen-coated plastic surface. The gel is then removed and the preparation is incubated with enzyme-conjugated anti-immunoglobulin. The enzyme is then visualised in situ by a colour reaction produced by pouring a substrate-containing gel over the plastic surface. Bovine serum albumin and rabbit-anti-BSA were used as a model system, and horseradish peroxidase or alkaline phosphatase as enzymes for visualization.