Physalin B inhibits Rhodnius prolixus hemocyte phagocytosis and microaggregation by the activation of endogenous PAF-acetyl hydrolase activities.
The effects of physalin B (a natural secosteroidal chemical from Physalis angulata, Solanaceae) on phagocytosis and microaggregation by hemocytes of 5th-instar larvae of Rhodnius prolixus were investigated. In this insect, hemocyte phagocytosis and microaggregation are known to be induced by the platelet-activating factor (PAF) or arachidonic acid (AA) and regulated by phospholipase A(2) (PLA(2)) and PAF-acetyl hydrolase (PAF-AH) activities. Phagocytic activity and formation of hemocyte microaggregates by Rhodnius hemocytes were strongly blocked by oral treatment of this insect with physalin B (1mug/mL of blood meal). The inhibition induced by physalin B was reversed for both phagocytosis and microaggregation by exogenous arachidonic acid (10microg/insect) or PAF (1microg/insect) applied by hemocelic injection. Following treatment with physalin B there were no significant alterations in PLA(2) activities, but a significant enhancement of PAF-AH was observed. These results show that physalin B inhibits hemocytic activity by depressing insect PAF analogous (iPAF) levels in hemolymph and confirm the role of PAF-AH in the cellular immune reactions in R. prolixus.
Castro
D P
DP
Laboratório de Bioquímica e Fisiologia de Insetos, Instituto Oswaldo Cruz, Fundação Oswaldo Cruz, RJ, Brazil.
Figueiredo
M B
MB
Genta
F A
FA
Ribeiro
I M
IM
Tomassini
T C B
TC
Azambuja
P
P
Garcia
E S
ES
D043203:1-Alkyl-2-acetylglycerophosphocholine Esterase / Q000378:metabolism*; D000818:Animals; D016718:Arachidonic Acid / Q000494:pharmacology; D002449:Cell Aggregation / Q000187:drug effects; D004789:Enzyme Activation / Q000187:drug effects; D006434:Hemocytes / Q000187:drug effects / Q000201:enzymology / Q000276:immunology* / Q000382:microbiology; D019476:Insect Proteins / Q000378:metabolism*; D010587:Phagocytosis / Q000187:drug effects*; D010972:Platelet Activating Factor / Q000494:pharmacology; D012239:Rhodnius / Q000187:drug effects / Q000201:enzymology* / Q000276:immunology / Q000382:microbiology; D012441:Saccharomyces cerevisiae / Q000502:physiology; D012632:Secosteroids / Q000494:pharmacology*
D019476:Insect Proteins; D010972:Platelet Activating Factor; D012632:Secosteroids; C033270:physalin B; D016718:Arachidonic Acid; D043203:1-Alkyl-2-acetylglycerophosphocholine Esterase