Of pigs and peptides: interactions between Host Defence Peptides, Streptococcus suis and Porcine Immune Cells

Abstract

There are almost one billion pigs worldwide, which are threatened by pathogenic bacteria. One of those is Streptococcus suis. There is no effective vaccine against this bacterium, leading to many diseased pigs each year, which in turn poses risks to humans. Treatment with antibiotics is possible, but in pigs the infection must be diagnosed in time, and treatment could lead to antibiotic resistance development. One solution for S. suis infections could be the host defence peptides (HDPs). HDPs are antimicrobial without inducing resistance and have immune modulatory functions which make them suitable as vaccine components. However, there is a lack of specific knowledge of HDP activity in porcine cell systems, and particularly in the context of an S. suis infection. The HDP CATH-2 is effective in inhibiting the immune response of porcine macrophages. This could be important in, for example, effective vaccines that have sizable side effects. S. suis has a remarkable resilience to HDPs originating in pigs, but much less against CATH-2. More research is needed to clarify the mechanism of resilience. CATH-2 effectively inhibits porcine dendritic cell activation by both E. coli and S. suis. This could mean that CATH-2 could potentially lower side effects of a vaccine, without damaging the capacity to process the antigen (and thereby the vaccine effectivity). CATH-2 and some derivatives have the potential to protect mice against S. suis induced disease symptoms. These CATH-2 derivatives could be used prophylactically, although this has not yet been tested in pigs.