A Precipitin Test for Typhoid Fever

Abstract

TREATMENT of typhoid fever with the serum from convalescents of this disease is a well-recognized therapeutic procedure. The good results obtained are believed to be due to passive immunization, as in other forms of serum therapy. From the serological analysis of a large number of convalescent typhoid sera it was, however, observed that their antibody content, both of O and Vi antibodies, was universally poor. On the other hand, in spite of their paucity in antibodies, such sera had proved to be very efficacious therapeutic agents in our hands during the last few years. This experience could not, therefore, be reconciled with the statements of Felix and his co-workers on the important role of Vi antibody, and its antigenic counterpart, in typhoid immunity and infection ; in fact, this antibody forms the principal constituent of Felix's therapeutic antityphoid serum. Further experiments were, therefore, undertaken which revealed that when a convalescent serum was injected into human beings, as well as laboratory animals, it led to the production of an appreciable amount of Vi antibody and that its therapeutic efficacy was directly proportional to the amount of antibody so produced. These observations could only be explained by assuming that the convalescent serum either stimulated the antibody-forming apparatus in some unknown manner or that it contained an antigen responsible for Vi antibody formation. It has now been ascertained that the latter explanation is correct and the typho-precipitin reaction reported here is based on the presence of a Vi precipitinogen in the sera of typhoid patients both during infection and during convalescence. The qualitative and quantitative determination of this antigen has been found to be of definite significance in the diagnosis, the prognosis and the treatment of typhoid fever.