Distribution-analyzing latex immunoassay (DALIA): methods for determination of antigen and for elimination of non-specific reaction induced by rheumatoid factor.

A highly sensitive distribution-analyzing latex immunoassay method (DALIA), which is based on analysis of the volume distribution of latex particles including both the agglutinates and the residual non-agglutinating particles, has been established. Numbers of latex particles, which are sensitized with specific antibodies, are counted by using an electric particle counter with a personal computer and simultaneously the extent of agglutination was quantified by analyzing the volume distribution of the reacted latex particles. It was found that ultramicrospheres coated with normal goat immunoglobulin G can completely eliminate non-specific reactions induced by human serum containing rheumatoid factor (RF) in this DALIA method. The degree of absorption of RF activity by these ultramicrospheres was associated with the diameters of the ultramicrospheres. Moreover, by use of the combination of ultramicrospheres and latex particles coated with monoclonal antibodies against alpha-fetoprotein (AFP) or with polyclonal antibody specific to C-reactive protein, specific DALIA systems were able to be developed. Both DALIA systems exhibited the high sensitivity (1 to 7 ng/ml). The correlation coefficient (gamma) of the results of DALIA with those of enzyme-linked immunoadsorbent assay in measuring AFP was 0.994.