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Bacterial formyl peptide mediated chemotaxis and extracellular acidification in shrimp haemocytes
1Biology Department, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong.
Abstract:
The bacterial formyl peptide N-formylmethionine-leucine-phenylalanine (fMLP) is a potent chemoattractant for mammalian neutrophils. In this study, we demonstrated the binding of fluorescent dye-conjugated-fMLP to haemocytes of the penaeid shrimp Penaeus penicillatus (Alcock), through the use of flow cytometry. Fluorescence microscopy with rhodamine-fMLP suggested that fMLP receptors are present only in sub-populations of the haemocytes: granulocytes and the semi-granular cells. In addition, fMLP dose-dependently mediated chemotaxis in sub-populations of haemocytes. Microphysiometry experiments demonstrated rapid extracellular acidification upon addition of fMLP, which is in agreement with the observation in neutrophils. t-BOC, the specific fMLP receptor antagonist, was able to block the binding, chemotaxis and extracellular acidification induced by the peptide. The ability of shrimp haemocytes to migrate toward fMLP in vitro suggests that this mechanism may be important for the accumulation of these cells in infected tissues of the shrimps.
Insights
This study shows that shrimp immune cells (haemocytes) bind and respond to bacterial N-formylmethionine-leucine-phenylalanine (fMLP), a key molecule in mammalian immunity. This suggests a conserved immune signaling pathway in invertebrates.
Area of Science:
- Immunology
- Marine Biology
- Cell Biology
Background:
- N-formylmethionine-leucine-phenylalanine (fMLP) is a bacterial peptide known to attract mammalian neutrophils.
- Immune responses in invertebrates, like shrimp, involve complex cellular interactions and signaling pathways.
Purpose of the Study:
- To investigate the presence and function of fMLP receptors on shrimp haemocytes.
- To determine if fMLP can elicit an immune response in penaeid shrimp (Penaeus penicillatus).
Main Methods:
- Flow cytometry and fluorescence microscopy were used to detect fMLP binding to shrimp haemocytes.
- Chemotaxis assays and microphysiometry were employed to assess haemocyte response to fMLP.
- The effect of the fMLP receptor antagonist t-BOC was evaluated.
Main Results:
- Fluorescently labeled fMLP bound to specific subpopulations of Penaeus penicillatus haemocytes (granulocytes and semi-granular cells).
- fMLP induced dose-dependent chemotaxis and extracellular acidification in these haemocytes, similar to mammalian neutrophils.
- The fMLP receptor antagonist t-BOC effectively blocked fMLP-induced binding, chemotaxis, and acidification.
Conclusions:
- Shrimp haemocytes possess functional fMLP receptors, indicating a conserved chemoattractant signaling pathway.
- This fMLP-mediated mechanism may play a role in the recruitment of shrimp haemocytes to sites of infection.
- The findings provide insights into invertebrate innate immunity and potential targets for disease control in aquaculture.