Immunogenicity of trypsin treated type 2 and type 3 poliovirus in rats

Oral polio vaccine will encounter the proteolytic enzyme trypsin during administration but inactivated polio vaccine not. To investigate the effect on the humoral immune response, rats were immunized intramuscularly with trypsin treated type 2 and type 3 poliovirus. IgG and IgM responses were determined as well as the neutralizing antibody titer. It is shown that the immunogenicity of type 2 poliovirus, unlike that of type 3, is hardly affected by trypsin treatment. For type 3, trypsin treatment results in an increase in IgM and neutralizing response. The IgG response decreases after trypsin treatment. The results indicate that IPV formulations may be improved by the addition of trypsin treated type 3, as suggested by Roivainen and Hovi (J Virol 1987; 61: 3749-3753) but not by the addition of trypsin treated type 2 poliovirus.