In order to cause infections and circumvent eradication by the host’s immune defence, the common Streptococcus bacteria require several immune evasion strategies. A substantial part of the immune defence against bacterial pathogens is mediated by antibodies. Researchers at Umeå University have identified and characterised several new antibody degrading enzymes secreted by different Streptococcus species as a means to sabotage and evade antibody–mediated immune responses.

“My hopes are that the finding of these enzymes will improve the understanding of the mechanisms by which streptococci evade the host’s immune system during infections,” says Christian Spoerry, doctoral student at the Department of Molecular Biology and author of the doctoral dissertation.

Together with his research colleagues, Christian Spoerry found that members of the newly discovered IgdE enzyme family were shown to specifically degrade certain antibody subtypes of the respective Streptococcus species’ main host. The observed specificity of IgdE enzymes could therefore explain why certain Streptococcus species only infect certain host species, such as humans, pigs or horses, and not others. Characterization of these enzymes gives insights into the co–evolution process between pathogens and their hosts.

The abundance of antibody degrading enzymes among Streptococcus species indicates that they play an important role in the bacteria’s evasion from the antibody mediated immune responses. These novel identified antibody degrading enzymes, belonging to the IdeS and IgdE enzyme families, are thus potential valid vaccine targets and are of biotechnological use during the development of antibody based drugs.

Streptococci are highly host–specific pathogens that, depending on their host’s immune status as well as other circumstances, can cause mild to very severe infections – from skin infections to necrotizing fasciitis, commonly known as flesh–eating disease.

“The fascinating evolutionary interplay between the host immune system on the one hand and the Streptococci bacterium’s ability to evade those defences on the other could be described as a molecular level arms race. More research is needed, but these bacterial enzymes that we describe have potential as vaccines especially in veterinary medicine. This is of course critically important today amid growing alarms of antibiotic–resistant bacteria in livestock,” says Christian Spoerry.

Christian Spoerry is from Switzerland and moved to Sweden in 2006 to combine undergraduate studies in Biomedicine at Umeå University with elite level ski–orienteering. He is currently a doctoral student at the Department for Molecular Biology.