Differential agglutination of particulate Vi and O antigens by the IgM and IgG class antibodies.

The IgG and IgM immunoglobulins were fractionated from pooled sera of typhoid patients and typhoid carriers and the agglutinin titres and weights of Vi and O antibodies in these immunoglobulin fractions determined. The O antigen particles were more effectively agglutinated than the Vi antigen particles by their corresponding antibodies of the IgM class. There was no such difference between IgG class Vi and O antibodies. Similar behaviour was found on indirect estimation of the agglutination capacity of the IgG and IgM class Vi and O antibodies in the sera of individual typhoid patients or carriers. The significance of such differential agglutinating capacity of the Vi and O antibodies of the IgM class is discussed.