Effects of srtA variation on phagocytosis resistance and immune response of Streptococcus equi.

The research investigates the effect of alterations in the srtA gene of the Streptococcus equi bacteria (the cause of equine disease “Strangles”) on the bacteria’s resistance to phagocytosis and the resultant immune response. The study found that specific mutations either increased the bacteria’s resistance to immune response or decreased the bacterial load in the host.

Objective of Study

• In this research, the authors aimed to understand how the mutation in the srtA gene affects the ability of the Streptococcus equi bacteria to resist being engulfed by immune cells (phagocytosis) and how it impacts the overall immune response.

Study Design

• The researchers used three types of sortase A (srtA) proteins: srtA-HT1112 (I88V), srtA-5012 (R147G), and srtA-ZZM17 (control), which were created by performing point mutations on the srtA gene.
• These proteins were expressed, purified, and then used to immunize mouse models. The researchers then observed the phagocytic activity of the immune cells and analyzed the amount of the bacteria present in the mice.

Results and Findings

• The srtA-HT1112 (I88V) mutation displayed enhanced resistance to phagocytosis and also increased adherence inhibition activity which implies its higher capacity to resist immune responses.
• In contrast, the srtA-5012 (R147G) mutation showed high levels of IgG2a (an immune response marker) and a high protection rate between 62.5% to 75%. Importantly, the bacterial load in the lung was lowest for this mutation, indicating a more effective immune response.
• The study suggests that the I88V mutation in the srtA gene makes the bacteria more immune-resistant, whereas the R147G mutation results in robust immune reactions and lower bacterial load.

Implications of results

• This research helps to deepen our understanding of the genetic variations in the Streptococcus equi bacteria that influence its ability to resist the host’s immune response.
• The findings could guide the development of more effective vaccines against infectious diseases caused by this bacteria as it provides an understanding of how the bacteria evade immune responses and which mutations result in stronger immune responses.