Detection and characterization of phenoloxidasse in Chironomus riparius

• Autor(a) principal: Fernandes, Sónia Rafaela Beleza
• Data de Publicação: 2018
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10773/22027
• topic: Sistema imunitário - Insectos; Fenoloxidase

Insects are frequently exposed to a large variety of microbes, microorganisms and parasites which requires an effective immune system of defence against infections. However, insects lack an adaptive immune system, so they have developed other highly effective systems of host defence, such as innate immune reactions. These innate immune reactions refer to the first-line of defence of hosts against bacterial, fungal, and viral pathogens. Research on invertebrate model systems have been increasing and becoming very important in ecological immunology research. One of the most important immune component used by insects is melanogenesis, which is responsible for encapsulation followed by melanization of the pathogens. Melanization requires activation of a key enzyme – phenoloxidase (PO), during PO cascade which is the major humoral immune effector system. Due to the importance of PO on insect immune system, the aims of the present study were to characterize PO activity in samples of C. riparius larvae whole body homogenates, and evaluate the sensitivity of PO activity as an indicator of effects of two widely used bio insecticides - Naturalis®-L and VectoBac® 12AS. The results demonstrated that proPO present in C. riparius samples was readily activated by the presence of chymotrypsin, zymosan and lipopolysaccharide. On the other hand, 1-phenyl-2-thiourea inhibited PO activity. In vivo exposures, PO activity was significantly increased ~ 5 and 6 abs / mg protein in samples exposed to 2 and 5 mg/L of Naturalis®-L and ~ 4 abs / mg protein in samples exposed to 20 ng/L VectoBac® 12AS, in comparison with unexposed organisms (~ 2 abs/mg of protein). This activity increased even more with the presence of chymotrypsin. Also the results suggest de novo synthesis of proPO under exposure to bio insecticides. Thus, this study confirmed the presence of a true PO, due to the inhibition caused by the PTU. We concluded that the measurement of PO activity and activation of proPO can and should be used as an immunological biomarker, providing information on the immunological status of the organism and on sub-lethal responses to stress.