Microgravimetric determination of precipitable antigens and antibodies in native biological fluids

A method for the exact and simultaneous measurements of immunoprecipitable antigens and antibodies in native biological fluids is described. It is based solely on the microgravimetric analysis of at least two immunoprecipitates of different stoichiometric compositions. The volume ratios of antigen and antibody solutions for the preparation of the immunoprecipitates at equivalence are determined by the two-cross immunodiffusion technique. The proposed procedure has advantages over other methods for quantitative determination of proteins, since the separation, purification and labelling of immune components, as well as the use of standards, are not required. The method was tested by using human serum albumin (HSA) and three rabbit antiHSA immune sera of various avidities. Immunoprecipitates of different stoichiometric compositions were prepared at pH 5.0, 5.5, 7.0 and 8.6. The minimal precision of the method was +/- 0.2 micrograms of protein. The coefficients of variation were 0.14 to 0.38% for HSA and 0.03 to 0.08% for antiHSA antibody.