Immunoprotection from Streptococcus suis serotype 2 suilysin and its antiserum

Objective To investigate the immunoprotection of Streptococcus suis serotype 2(SS2) suilysin(SLY) and its antiserum.Methods Mice were immunized with the purified SLY recombinant protein.The antiserum against SLY was collected and used to determine the specific antibody titers and IgG isotypes.Subsequently,the active immunized mice were challenged with a lethal dose of S.suis 2.Moreover,the immunoprotection of SLY was evaluated.The antiserum against SLY was used passively to immunize the mice,which were challenged with a lethal dose of S.suis 2 after four hours.The protection provided by the antiserum against S.suis 2 was evaluated.Results The antiserum for mice immunized with recombinant protein SLY was collected.The titer reached 1∶25600,containing IgG1and IgG2a,two kinds of subtype antibodies.However,the difference between IgG1 and IgG2a was not significant.All actively immunized mice were injected with a lethal dose of S.suis 2.The survival rate of the actively immunized mice was significantly higher(60%) than that of the control group(10%)(P < 0.05).Mice that are passively immunized with SLY antiserum were challenged with a lethal dose of S.suis 2.On the 7th day after challenge,the survival rate was significantly higher(90%) than that in the control group(20%)(P < 0.05).Significant differences in survival rates were not observed between the passively immunized and the control group(P > 0.05) 14 days after the challenge.Conclusions SLY and SLY-specific antiserum provides immunoprotection.