Last updated July 16, 2018 at 5:20 pm
A mosquito bite alone, without pathogens, can affect your immune system for up to a week.
Mosquito bites are the bane of every Australian during summer. Their bite – and more specifically, their saliva – packs a powerful punch, as researchers have published this week. This is the first study to look at mosquito saliva on human immune cells in a living mice, transmitted through a mosquito bite.
Understanding mosquito-transmitted diseases is a high global priority, with diseases such as malaria, Zika, dengue, West Nile, and chikungunya fever. Mosquitoes carry and spread disease to humans causing millions of deaths each year.
A mosquito can transfer viruses to humans through a bite but there’s a lot more to that itch-inducing bite. Mosquito saliva contains more than 100 proteins, most with unknown functions.
For the first time, researchers have shown that these proteins can elicit an immune response from the human immune system, resulting in this response sticking around for days after a bite.
The specific properties of a mosquito bite, including their saliva, can exacerbate some diseases. In mice, infections caused by a mosquito bite are often more severe than those via needle injection of the parasite.
To study the effect of mosquito bites on immune cells, scientists grafted mice with human stem cells to mimic a human immune system.
The human immune response is a complex system of different types of immune cells reacting in a way to fight the pathogen. More complicated is that different responses occur at different time points after an infection. Monitoring all these different immune cells tells scientists if something is triggering an immune response.
In this study, the mice were bitten by uninfected mosquitoes, on their feet – one of the worst places to get a mosquito bite! Several types of human immune responses were seen, including the triggering of immune T cells changing into subsets of cells known T helper cells (Th1 and Th2).
Mosquito saliva in the humanised mice altered the number or frequency of several types of immune cells in different tissues (blood, skin, spleen, bone marrow) at different time points (6 hours, 24 hours, and 7 days post-bite).
Cytokines are also an important player, they’re chemical responses created by immune cells which can amplify an effective immune response. The mosquito saliva had mixed effects on specific cytokines with some increases and some decreases. These dynamic effects varied and continued to be evident even at 7 days post-bite.
The study shows that mosquito saliva can make a considerable effect on the human immune response. The authors speculate it could be possible that the saliva is helping the virus to downplay the immune response so that it can evade the immune system and replicate with higher success.
“Understanding how mosquito saliva interacts with the human immune system not only helps us understand mechanisms of disease pathogenesis but also could provide possibilities for treatments,” the researchers say.
This research was published in PLOS Neglected Tropical Diseases.