Serotonin modulates insect hemocyte phagocytosis via two different serotonin receptors

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Abstract

Serotonin (5-HT) modulates both neural and immune responses in vertebrates, but its role in insect immunity remains uncertain. We report that hemocytes in the caterpillar, Pieris rapae are able to synthesize 5-HT following activation by lipopolysaccharide. The inhibition of a serotonin-generating enzyme with either pharmacological blockade or RNAi knock-down impaired hemocyte phagocytosis. Biochemical and functional experiments showed that naive hemocytes primarily express 5-HT_1B and 5-HT_2B receptors. The blockade of 5-HT_1B significantly reduced phagocytic ability, however the blockade of 5-HT_2B increased hemocyte phagocytosis. The 5-HT_1B-null Drosophila melanogaster mutants showed higher mortality than controls when infected with bacteria, due to their decreased phagocytotic ability. Flies expressing 5-HT_1B or 5-HT_2B RNAi in hemocytes also showed similar sensitivity to infection. Combined, these data demonstrate that 5-HT mediates hemocyte phagocytosis through 5-HT_1B and 5-HT_2B receptors and serotonergic signaling performs critical modulatory functions in immune systems of animals separated by 500 million years of evolution.

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Yixiang Qi

State Key Laboratory of Rice Biology and Key Laboratory of Agricultural Entomology of Ministry of Agriculture, Institute of Insect Sciences, Zhejiang University, Hangzhou, China

Competing interests
The authors declare that no competing interests exist.
Jia Huang

State Key Laboratory of Rice Biology, Key Laboratory of Agricultural Entomology of Ministry of Agriculture, Institute of Insect Sciences, Zhejiang University, Hangzhou, China

For correspondence
huangj@zju.edu.cn

Competing interests
The authors declare that no competing interests exist.
Meng-qi Li

State Key Laboratory of Rice Biology, Key Laboratory of Agricultural Entomology of Ministry of Agriculture, Institute of Insect Sciences, Zhejiang University, Hangzhou, China

Competing interests
The authors declare that no competing interests exist.
Ya-su Wu

State Key Laboratory of Rice Biology, Key Laboratory of Agricultural Entomology of Ministry of Agriculture, Institute of Insect Sciences, Zhejiang University, Hangzhou, China

Competing interests
The authors declare that no competing interests exist.
Ren-ying Xia

State Key Laboratory of Rice Biology, Key Laboratory of Agricultural Entomology of Ministry of Agriculture, Institute of Insect Sciences, Zhejiang University, Hangzhou, China

Competing interests
The authors declare that no competing interests exist.
Gong-yin Ye

State Key Laboratory of Rice Biology, Key Laboratory of Agricultural Entomology of Ministry of Agriculture, Institute of Insect Sciences, Zhejiang University, Hangzhou, China

Competing interests
The authors declare that no competing interests exist.

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