Latex particles sensitized with proteins of Leptospira interrogans for application in immunoagglutination assays

Abstract

ABSTRACTPhysical adsorption and chemical coupling of recombinant proteins of Leptospira interrogans onto polystyrene and core-shell carboxylated particles were, respectively, investigated with the aim of producing latex–protein complexes to be used in immunoagglutination assays able to detect the leptospirosis disease in either humans or animals. To this effect, a protein lysate of crude extracts was evaluated, and sensitizations were carried out at different pHs, with the antigenic proteins approach to the particle surface favored at pH close to their isoelectric point. In the covalent coupling experiments, high fractions of proteins were chemically bound to carboxyl groups on the particle surface and higher densities of linked proteins were obtained for particles exhibiting greater carboxyl group densities. The produced latex–protein complexes were tested in immunoagglutination assays, by turbidimetry and a visual method, from a panel that included positive and negative bovine, canine, and human sera. The area under receiver operating characteristic curves was used as an index of accuracy. The complexes obtained by covalent coupling of proteins on the latex of higher density of carboxyl groups allowed an acceptable discrimination between the studied positive and negative sera.