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External amebocytes guard the pharynx entry in a tunicate (Ascidiacea)
Francesca Cima1, Loriano Ballarin, Fabio Gasparini
1Dipartimento di Biologia, Università di Padova, Via U. Bassi 58/B, 35100 Padova, Italy. francesca.cima@unipd.it
Developmental and Comparative Immunology
|September 27, 2005
Summary
Free amebocytes in the ascidian Botryllus schlosseri were identified as sentinel cells. These cells share phagocytic markers with blood cells, indicating a role in immune surveillance.
Area of Science:
- Marine biology
- Invertebrate immunology
- Cell biology
Background:
- Compound ascidians like Botryllus schlosseri possess a unique immune system.
- The role of free amebocytes in ascidian siphons remains largely uncharacterized.
Purpose of the Study:
- To identify and characterize unusual free amebocytes found in the siphons of Botryllus schlosseri.
- To investigate the origin and biological function of these siphon-associated amebocytes.
Main Methods:
- Cytochemical and ultrastructural analysis of amebocytes.
- Histochemical, histoenzymatic, and immunohistochemical assays on hemocytes.
- Light microscopy on fixed and cultured cells.
- Phagocytosis assays using carmine particles.
Main Results:
- Free amebocytes in the oral and atrial siphons were identified.
- These cells exhibited characteristics of phagocytic blood cells, including NPA agglutinin affinity and lysosomal enzyme activity.
- Cells were labeled with PKH26 and anti-CD39, similar to mammalian macrophages.
- Amebocytes demonstrated phagocytic activity towards carmine particles.
Conclusions:
- The identified amebocytes are proposed to be 'sentinel cells' of the hyaline amebocyte population.
- These cells are part of the phagocytic differentiation line of immunocytes.
- They play a role in recognizing and phagocytizing foreign particles, contributing to ascidian immunity.