Innate immunity in insects: surface-associated dopa decarboxylase-dependent pathways regulate phagocytosis, nodulation and melanization in medfly haemocytes
Article first published online: 5 NOV 2007
© 2007 The Authors
Volume 123, Issue 4, pages 528–537, April 2008
How to Cite
Sideri, M., Tsakas, S., Markoutsa, E., Lampropoulou, M. and Marmaras, V. J. (2008), Innate immunity in insects: surface-associated dopa decarboxylase-dependent pathways regulate phagocytosis, nodulation and melanization in medfly haemocytes. Immunology, 123: 528–537. doi: 10.1111/j.1365-2567.2007.02722.x
- Issue published online: 9 JAN 2008
- Article first published online: 5 NOV 2007
- Received 10 July 2007; revised 10 and 22 August 2007; accepted 22 August 2007.
- dopa decarboxylase;
- insect innate immunity;
Phagocytosis, melanization and nodulation in insects depend on phenoloxidase (PO) activity. In this report, we demonstrated that these three processes appear to be also dependent on dopa decarboxylase (Ddc) activity. Using flow cytometry, RNA interference, immunoprecipitation and immunofluorescence, we demonstrated the constitutive expression of Ddc and its strong association with the haemocyte surface, in the medfly Ceratitis capitata. In addition, we showed that Escherichia coli phagocytosis is markedly blocked by small interfering RNA (siRNA) for Ddc, antibodies against Ddc, as well as by inhibitors of Ddc activity, namely carbidopa and benzerazide, convincingly revealing the involvement of Ddc activity in phagocytosis. By contrast, latex beads and lipopolysaccharide (LPS) did not require Ddc activity for their uptake. It was also shown that nodulation and melanization processes depend on Ddc activation, because antibodies against Ddc and inhibitors of Ddc activity prevent haemocyte aggregation and melanization in the presence of excess E. coli. Therefore, phagocytosis, melanization and nodulation depend on haemocyte-surface-associated PO and Ddc. These three unrelated mechanisms are based on tyrosine metabolism and share a number of substrates and enzymes; however, they appear to be distinct. Phagocytosis and nodulation depend on dopamine-derived metabolite(s), not including the eumelanin pathway, whereas melanization depends exclusively on the eumelanin pathway. It must also be underlined that melanization is not a prerequisite for phagocytosis or nodulation. To our knowledge, the involvement of Ddc, as well as dopa and its metabolites, are novel aspects in the phagocytosis of medfly haemocytes.