Two biogenic monoamines, octopamine and 5-hydroxytryptamine (5-HT), are known to play immune mediators in insects. They induce hemocyte behaviors by stimulating cytoskeleton rearrangement. However,it is not clear how they activate the hemocytes in terms of intracellular signal transduction. This study analyzed their interactions with signal pathways implicated in nodule formation via eicosanoids or hemocyte locomotory behavior via a small GTPase. Both octopamine and 5-HT increased hemocytic nodule formation in response to bacterial challenge in the beet armyworm, Spodoptera exigua. However, their immune mediation was inhibited by a treatment of dexamethasone (a specific inhibitor to phospholipase A2). In the presence of phentolamine (a specific antoganist to octopamine) or ketanserin (a specific antoganist to 5-HT), the inhibitory activity of dexamethasone was rescued by adding arachidonic acid (a precursor of eicosanoid biosynthesis). These results suggest that the mediation of nodule formation by the two monoamines is followed by eicosanoid signaling. Two monoamines also induced up-regulation of circulating hemocyte counts in S. exigua. This increase of hemocyte counts was not explained by de novo production of hemopoietic organ because even ligation between thorax and abdomenin order to block hemolymph circulation did not inhibit the increase of circulating hemocyte counts by octopamine.A small GTPase, Rac1, appeared to be involved in this hemocyte mobilization from a sessile compartment in S. exigua. Inhibition of Rac1 activity significantly suppressed hemocyte spreading behavior and the hemocyte mobilization. In summary, octopamine and 5-HT mediate cellular immune responses of S. exigua via eicosanoid signal or independently by activating Rac1 following increase of cAMP in the hemocytes.

세로토닌 수용체는 세로토닌과 반응하여 세포막의 G단백질을 통해 중개단백질 (adenylyl cyclase, phospholipase C, cGMP phosphodiesterase, ion channel)을 활성화시켜, 이뇨, 기억, 발생 등의 다양한 생리적 반응에 관여한다. 곤충세포인 Schneider2 (S2)와 척추동물 세포인 Chinese hamster ovary (CHO)-Kl에서 Aedes 5-HT 수용체 유전자 발현을 비교하기 위해, Aedes 5-HT 수용체 유전자를 형질이입시켰다. 선발된 세포주들(Tr-S2, Tr-CHO)에서 세로토닌 수용체 유전자의 발현은 reverse transcription-PCR, Western blot, immunocytochemistry를 이용하여 확인하였다. 세로토닌 농도증가에 대한 Aedes 5-HT수용체의 기능을 세포 내 cAMP수준을 통해 조사한 결과,Tr-CHO 세포주는 Tr-S2 세포주보다 9배 이상 cAMP수준이 높게 나타났으며, 농도에 의존적이었다. 이 결과는 수용체 유전자가 세포에서 발현되었으나, 세포의 종류와 세포막에 존재하는 G단백질 차이에 따라 중개단백질 활성 차이가 있다는 것을 보여주었다. CHO-Kl 세포에서 Aedes 5-HT 수용체의 기능이 S2 세포보다 더 효율적이며, Aedes 5-HT 수용체를 발현하는 Tr-CHO 세포주는 동력제 또는 대립제 검정에 활용될 수 있을 것으로 기대된다. 것으로 기대된다.