Serotonin modulates insect hemocyte phagocytosis via two different serotonin receptors

• Main Authors: Yi-xiang Qi, Jia Huang, Meng-qi Li, Ya-su Wu, Ren-ying Xia, Gong-yin Ye
• Format: Article
• Language: English
• Published: eLife Sciences Publications Ltd 2016-03-01
• Series: eLife
• Subjects: serotonin receptor; hemocyte; phagocytosis; innate immunity; bacteria infection
• Online Access: https://elifesciences.org/articles/12241

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-HT1B and 5-HT2B receptors. The blockade of 5-HT1B significantly reduced phagocytic ability; however, the blockade of 5-HT2B increased hemocyte phagocytosis. The 5-HT1B-null Drosophila melanogaster mutants showed higher mortality than controls when infected with bacteria, due to their decreased phagocytotic ability. Flies expressing 5-HT1B or 5-HT2B RNAi in hemocytes also showed similar sensitivity to infection. Combined, these data demonstrate that 5-HT mediates hemocyte phagocytosis through 5-HT1B and 5-HT2B receptors and serotonergic signaling performs critical modulatory functions in immune systems of animals separated by 500 million years of evolution.