Development of a polystyrene latex-based reagent for rheumatoid factor detection

Abstract

Abstract A rapid, specific and sensible polystyrene latex-based reagent has been developed to detect rheumatoid factor (RF) in human sera. Detection of RF is one of the criteria for rheumatoid arthritis (RA) diagnosis. RF includes immunoglobulins IgG, IgM or IgA targeting human-IgG Fc region, found in sera of 70–90% of patients with RA. Spherical, clean polystyrene particles of 480±80 nm with a Z-potential of -28 mV were synthesized. Purified gamma-globulin human blood fraction, used as IgG source, was adsorbed on particles in glycine-buffered saline with a fivefold excess of the immunoglobulins needed to saturate the calculated total surface area of the particles. The reagent was calibrated against the World Health Organization international serum reference preparation and tested with commercial positive and negative RF controls. Reactivity of the developed diagnostic reagent with human sera, either positive or negative for RF, was evaluated. The sera were tested both intact and following complement inactivation. When complement-inactivated sera were used, our reagent showed 100% coincidence of results with a commercial diagnostic kit of specificity of 80% and sensibility of 93%. The in-house reagent developed in the present work is easy to prepare and at relatively low cost, making it ideal for RF detection in low-income settings.