Vaccination with the immunoglobulin M-degrading enzyme of Streptococcus suis, IdeSsuis, leads to protection against a highly virulent serotype 9 strain

Abstract

Vaccination of weaning piglets with the recombinant IgM degrading enzyme of Streptococcus suis (S. suis), rIdeSsuis, elicits protection against disease caused by serotype (cps) 2 infection. In Europe, S. suis cps9 is at least as important as cps2 in causing severe herd problems associated with meningitis, septicemia and arthritis. The objective of this study was to determine humoral and cellular immunogenicities of rIdeSsuis suckling piglet vaccination and to investigate protection against a virulent cps9 strain. Vaccination in the 2nd and 4th week of life with rIdeSsuis and an oil-in-water adjuvant induced seroconversion against IdeSsuis in 13 of 20 vaccinated piglets. In the 5th week, survival of the S. suis cps9 strain was significantly reduced in the blood of prime-booster vaccinated piglets. After a 2nd booster vaccination IdeSsuis-reactive T helper (Th) cells partially producing TNF-α, IL-17A or IFN-ɣ were detectable in rIdeSsuis-vaccinated but not in placebo-treated piglets and frequencies of IdeSsuis-reactive Th cells correlated with α-IdeSsuis–IgG levels. An intravenous challenge, conducted with a cps9 strain of sequence type (ST) 94, led to 89% mortality in placebo-treated piglets due to septicemia and meningitis. In contrast, all rIdeSsuis prime-booster-booster vaccinated littermates survived the challenge despite signs of disease such as fever and lameness. In conclusion, the described rIdeSsuis vaccination induces humoral and detectable IdeSsuis-reactive Th cell responses and leads to protection against a highly virulent cps9 strain.