Insight into how tick saliva suppresses cattle immunity

Scientists from Hokkaido University, Universidade Federal do Rio Grande do Sul and Universidade Federal do Rio de Janeiro have revealed that substances in tick saliva activate immune response-suppressing proteins in cattle that facilitates the transmission of tick-borne diseases. The finding, published in Scientific Reports, could help in the development of alternative control strategies.

The researchers studied the Asian blue tick, Rhipicephalus microplus, which feeds on cattle, causing skin lesions, chronic blood loss and transmission of pathogens.

Some ticks have developed resistance against currently used acaricides. To develop alternative strategies that can better protect cattle, such as vaccines, scientists need to better understand tick infections at the molecular level. Scientists already know that tick saliva suppresses the immune response in cattle, facilitating the transmission of tick-borne pathogens, but the exact process has not been fully clarified.

The researchers investigated what happens to immune cells when they are exposed to tick saliva. The team found that substances in tick saliva, likely a prostaglandin, increase the expression of two specific cellular membrane proteins on some immune cells. The interaction of these proteins, called programmed cell death protein 1 (PD-1) and programmed death-ligand 1 (PD-L1), leads to the suppression of helper T cells (Th1). This means that the animal’s immune response is less able to combat invading tick-borne pathogens.

Further investigation showed Asian blue tick saliva contains a high concentration of prostaglandin E2, which is known to induce PD-L1 expression. However future studies need to confirm if prostaglandin E2 plays a direct role in suppressing the cattle immune response. Also, since this study involved cells in the laboratory, the team says further research in live cattle is needed.

Article: Sajiki, Y., Konnai, S., Ikenaka, Y., Gulay, K., Kobayashi, A., Parizi, L. F., João, B. C., Watari, K., Fujisawa, S., Okagawa, T., Maekawa, N., Logullo, C., da Silva Vaz, I., Jr, Murata, S., Ohashi, K. (2021). Tick saliva-induced programmed death-1 and PD-ligand 1 and its related host immunosuppression. Scientific Reports, 11(1), 1063, doi: 10.1038/s41598-020-80251-y

[SOURCE: Hokkaido University]