Methods for the purification of equine rabies immunoglobulin: effects on yield and biological activity

Since rabies is still a major cause of human death in many developing countries and the implementation of recommended post-exposure prophylaxis by vaccination and specific immunoglobulin therapy is largely hampered by its high cost, the development of cheap rabies vaccines and immunoglobulin preparation are a high priority in these countries. In this paper various purification methods of equine rabies immunoglobulin based on different principles are compared with respect to their effect on final yield and biological activity. It is shown that a combination of ammonium sulphate (AS) precipitation and DEAE ion exchange chromatography results in an acceptable recovery rate of biological activity and a product of relatively high purity. Although affinity chromatography with protein G in combination with AS precipitation results in a similar recovery rate and a product of considerably higher purity, the cost of this procedure may be prohibitive for routine use in most developing countries. The effects of pepsin digestion time on the biological activity of the product and on the reduction of intact horse Ig are also studied. The desirability of this digestion procedure with respect to reduction of adverse side effects and efficacy of the product for post-exposure treatment is discussed.