Morphologic, physiological and immunological changes of haemocytes from Litopenaeus vannamei treated by lipopolysaccharide

In this study, the cell size, viability, respiratory burst (RB) and mitochondrial membrane potential (MMP) of lipopolysaccharide (LPS)-treated haemocytes from Litopenaeus vannamei were measured by flow cytometry, and phenoloxidase (PO) activity of the cell supernatants was also determined. Three concentrations of LPS (1, 3 and 5 µg ml− 1) were used to determine the effects of LPS on haemocytes. The results revealed that haemocytes treated by LPS in vitro showed conspicuous dose- and time-dependent decreases in cell size and viability. The addition of trypsin inhibitor (TI) which inhibits serine proteinases further delayed the cell size reduction and cell death caused by LPS, implying that serine proteinases were involved in the cell responses. PO activities of the supernatants from LPS-treated cells were significantly higher than that from the control. These results indicated that cell size reduction caused by LPS appeared to be related to degranulation of semigranular and granular cells to release components of proPO system. RB activities were induced by LPS, but not by PMA. Sustaining and tremendous increase of RB occurred during the course of experiment, suggesting that LPS is a more efficient activator to RB of L. vannamei haemocytes than PMA. Specially, MMP of the LPS-treated haemocytes rose at first and then dropped, and which was significantly lower than that of control after 120 min incubation with LPS. The initial increase in MMP may have a relation to energy supply for cellular processes, and the later decrease of MMP represent cell apoptosis. Decreases on cell viability and MMP may be related to the overfull product of ROS which oxidized mitochondrial membrane and cell constituents. Though LPS stimulated PO activity of L. vannamei, LPS at the concentrations used in the present study is cytotoxic. These facts suggest that LPS should be carefully used as immunomodulator for shrimp.