Piglet innate immune response to Streptococcus suis colonization is modulated by the virulence of the strain

Abstract

Streptococcus suis is a zoonotic pathogen of swine involved in arthritis, polyserositis, and meningitis. Colonization of piglets by S. suis is very common and occurs early in life. The clinical outcome of infection is infuenced by the viru‑ lence of the S. suis strains and the immunity of the animals. Here, the role of innate immunity was studied in cesareanderived colostrum-deprived piglets inoculated intranasally with either virulent S. suis strain 10 (S10) or non-virulent S. suis strain T15. Colonization of the inoculated piglets was confrmed at the end of the study by PCR and immunohis‑ tochemistry. Fever (≥40.5 °C) was more prevalent in piglets inoculated with S10 compared to T15 at 4 h after inocula‑ tion. During the 3 days of monitoring, no other major clinical signs were detected. Accordingly, only small changes in transcription of genes associated with the antibacterial innate immune response were observed at systemic sites, with S10 inducing an earlier response than T15 in blood. Local infammatory response to the inoculation, evaluated by transcriptional analysis of selected genes in nasal swabs, was more sustained in piglets inoculated with the virulent S10, as demonstrated by transcription of infammation-related genes, such as IL1B, IL1A, and IRF7. In contrast, most of the gene expression changes in trachea, lungs, and associated lymph nodes were observed in response to the nonvirulent T15 strain. Thus, S. suis colonization in the absence of systemic infection induces an innate immune response in piglets that appears to be related to the virulence potential of the colonizing strain.