Comparison of IgM and IgG responses in mice sublethally infected with either S. suis serotype 3 or the SS2to3 mutant after primary and secondary infections showed no significant difference between the two strains (P > 0.05), although the primary IgG response was lower in mice infected with the SS2to3 mutant (Fig. 8C and F). Here, CD40LG is linked to infection.