Microgravimetric determination of precipitable antigens and antibodies in native biological fluids

Precipitation at equivalence and equilibrium: a method for the determination of equilibrium constants of reaction between multideterminant antigen and specific polyclonal antibodies

A theoretical approach for the determination of the equilibrium constant, Ka, of the reaction between a multideterminant antigen (Ag) and specific polyclonal antibodies (Ab) forming the insoluble Ab/Ag immune complex, is derived. The constant can be expressed as a function of the two accessible experimental parameters, the precipitating concentration of the antigen and the Ab/Ag molar ratio. For this purpose Ab/Ag immune complex must be prepared at equivalence, and equilibrium between precipitated and soluble species must be reached. The proposed method is experimentally tested on the system human serum albumin (HSA) and polyclonal rabbit antibodies. The Ab/Ag precipitates are prepared by the direct mixing of biological fluids in which immunoreacting components naturally occur. Previous separation, purification, or labeling of immunoreacting components are not required. The conditions for the precipitation of Ab/Ag complexes at equivalence, the stoichiometric composition or the average number of Ab molecules bound to one Ag molecule, and the solubility of the immunoprecipitating components are determined by a rectangular two-dimensional double immunodiffusion. Since the solubility determined under the conditions of a double immunodiffusion is a result of the interaction of the global diffusion of the precipitating components and particle growth kinetics, it mostly refers to the dynamic conditions. To find the solubility under equilibrium conditions, it is sufficient to determine the minimal factor by which the solutions of both immunoprecipitating components should be diluted so that no precipitate is formed upon their mixing at equivalence. The dilution factor is determined by a measurement of the laser light scattering of the immunoprecipitating systems prepared with serially diluted Ag and Ab solutions.

Quantitative and qualitative characterization of virus envelope proteins and specific polyclonal antibodies

A method for simultaneous qualitative and quantitative characterization of virus envelope proteins and virus-neutralizing antibodies is described. The quantitative estimate is based solely on the precipitation of the antibody/antigen (Ab/Ag) complexes at equivalence under equilibrium conditions. The qualitative analysis is performed by determining the diffusion coefficients, i.e., molecular masses of antigen and antibodies. Isolation, purification, labelling of antigen and antibodies and use of any standards are not required. The analyses are carried out directly in crude biological fluids in which antigen and antibodies naturally occur. The results obtained are independent on the avidity of the Ab/Ag system to be analysed. The method was tested by using antigenic subunits of Newcastle disease virus (NDV) and four chicken anti-NDV immune sera of different avidities.

Application of the immune complex for immune protection against viral disease

An immune complex (IC), composed of antigenic subunits of the Newcastle disease virus (NDV) and specific polyclonal allogeneic antibodies, was used to protect chickens against NDV. Antibodies in the IC were chicken immunoglobulin G. The antibody:antigen ratio in IC was 2.03. The IC was prepared at equivalence by direct mixing of NDV-infected allantoic fluid, treated with Triton X-100, and chicken anti-NDV serum. In order to bind NDV antigenic subunits to specific antibodies, previous isolation and purification of antigen is not required. Chickens were immunized with 1 mg IC, containing 0.3788 mg of viral antigens. The IC, prepared in the form of an oil-emulsion, was administered intramuscularly. The IC generated high levels of anti-NDV antibodies and successfully protected chickens against live virus challenge. Therefore, the IC could be recommended as a safe and environmentally convenient vaccine.