Coupling of foot-and-mouth disease virus to sheep red blood cells using tannic acid for immunological assays

A technique for coupling foot-and-mouth disease virus (FMDV) to tanned sheep red blood cells (SRBC) is reported. Different parameters influencing the procedure were studied. Subtypes C₂, C₃, O₁ and A₂₄ were used as antigens, and guinea pig hyperimmune sera obtained were tested for specific antibody in passive hemagglutination (PH), passive hemagglutination inhibition (PHI) and passive immune hemolysis (PIL) assays. Fresh and SRBC stored in Alsever's solution showed similar behavior when used as indicator cells. Optimal sensitization of erythrocytes was achieved using tannic acid 1:20000 and 20 μg of purified virus/ml at pH 7.6. Specificity of the reaction was confirmed by PH and PHI in homologous and heterologous systems. The coupled antigen-antibody complex was sensitive to complement mediated lysis in a PIL test.