COADSORPTION OF IGG AND BSA ONTO SULFONATED POLYSTYRENE LATEX .2. COLLOIDAL STABILITY AND IMMUNOREACTIVITY

The present work deals with the study of the colloidal stability and i mmunoreactivity of sulfonated polystyrene latex particles covered by d ifferent amounts of m-BSA and IgG/a-CRP. These proteins have been prev iously adsorbed onto a sulfonated latex by sequential and competitive coadsorption experiments and it was possible to obtain latex-protein p articles with different degrees of coverage by each protein. The latex particles, fully or partially covered by each protein (termed latex-p rotein complexes), were resuspended under several conditions (differen t pH and ionic strength values) and their colloidal stability, vs the addition of the electrolyte was studied using turbidity measurements. This stability appeared at a high degree of coverage by BSA and at a p H in which the BSA was negatively charged. At a high degree of coverag e by IgG, the latex particles were unstable at all pHs. As a final par t of this work, the immunoreactivity of several complexes was studied following the changes in the turbidity after the addition of CRP antig en. Only the complexes which were colloidally stable gave detectable r eactivity. However, the complexes with a relatively low degree of cove rage by IgG/a-CRP gave good immunoreactivity. Therefore, the latex-pro tein complex properties depended on the percentage of BSA or IgG adsor bed and on the electric state of the proteins at the redispersion pH. Under specific incubation conditions, sulfonated latex covered by sign ificant IgG/BSA percentages was obtained, which showed a high colloida l stability and good immunoreactivity.