Immune and circulatory programs are functionally built-in in all bugs, based on Vanderbilt Information

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Vanderbilt biologists have found solid evidence that among the insects of life, the functional relationship between the immune and circulatory systems is consistent. This will help researchers understand how insects – including the relatively few that transmit disease to animals or agricultural crops – fight, succumb, or transmit infections.

The article “The immune system and the circulatory system are functionally integrated into insect development” was published released in the magazine Advances in science on November 25th.

Professor of Biology Sciences Julián F. Hillyer investigates how mosquitoes fight infections and circulate their blood, two separate processes that affect each other. When mosquito immune cells discover a pathogen, they migrate to the heart and destroy the infection when the circulatory system brings them there. This process is similar to the way human immune cells migrate to areas of high blood flow such as the spleen and lymph nodes to fight infection.

On the left is a selection of the insects examined. The data show that, except for mayfly and flea, pathogens accumulate in the heart (blue peaks in the middle of the graphs, far left) and nowhere else. In addition, peaks in the rightmost graphs indicate that hemocytes accumulate in the periosteal regions along the length of the heart, except in silverfish, dragonflies, and stone flies, where they accumulate in the periosteal regions of the back of the heart. (Hillyer et al.)

Together with a PhD student Yan YanHillyer set out to investigate whether this process occurs in other insects. The researchers analyzed 68 insect species from 51 families representing 16 orders – a significant amount – to get a true cross-section of the insect biodiversity. Among the insects examined were the malaria mosquito and the yellow fever mosquito – two species that are as evolutionarily different as humans and whales – and bedbugs. Most of the insects were collected in the wild by Yan and her colleagues in various state parks approved by the Tennessee Department of Environment and Conservation.

“When we brought the insects into the lab, we used advanced microscopy techniques to look for discernible patterns between their hearts and immune responses to infection. In fact, we’ve seen the same behavior in most insects, which clearly showed us that the way their circulatory systems work is dramatically affected by the way their circulatory systems work, ”said Yan.

While some insects can be bothersome, scary, or dangerous, the vast majority are good for people and the planet. They cope with tasks that we cannot survive without, Hillyer explained, such as pollination of plants, aeration of the soil and the nutrient cycle through the ecosystem. “This makes the complete elimination of insects like mosquitoes unhealthy for the planet, although they are also responsible for spreading deadly diseases to humans and plants. After we have presented a clear picture of how insects’ immune and circulatory systems work together, researchers can develop techniques to alter their immune systems to prevent the transmission of diseases from insects to mammals or plants, ”he added.

Building on this work and previous research on the functional mechanics and timing of immune and circulatory processes in mosquitoes, the researchers are investigating the molecular mechanisms that cause the immune cell to reach the heart and how a disruption of this mechanism affects the insect .

Hillyer’s and Yan’s research was funded by NSF grants IOS-1456844 and IOS-1949145.

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