Oral polio vaccine will encounter the proteolytic enzyme trypsin durin
g administration but inactivated polio vaccine not. To investigate the
effect of trypsin on the humoral immune response, rats were immunized
intramuscularly with trypsin treated type 2 and type 3 poliovirus. Ig
G and IgM responses were determined as well as the neutralizing antibo
dy titer. It is shown that the immunogenicity of type 2 poliovirus, un
like that of type 3, is hardly affected by trypsin treatment. For type
3, trypsin treatment results in an increase in IgM and neutralizing r
esponse. The IgG response decreases after trypsin treatment. The resul
ts indicate that IPV formulations may be improved by the addition of t
rypsin treated type 3, as suggested by Roivainen and Hovi (J Virol 198
7; 61: 3749-3753) but not by the addition of trypsin treated type 2 po
liovirus.