The immunomodulation of a novel tumor necrosis factor (CgTNF-1) in oyster Crassostrea gigas

Tumor necrosis factor (TNF) is one of the most important cytokines involved in many processes in both vertebrate and invertebrate. In the present study, a new tumor necrosis factor with a typical TNF domain was identified in oyster Crassostrea gigas (designated CgTNF-1). CgTNF-1 shared low sequence identity and similarity with the TNF superfamily members from other vertebrate and invertebrate. After LPS stimulation, the mRNA expression of CgTNF-1 in haemocytes increased significantly and peaked at 12 h (1.39 ± 0.12, P < 0.05) post treatment, and the expression of CgTNF-1 protein in haemolymph also increased obviously during 6-12 h. When the oyster haemocytes were incubated with rCgTNF-1, its apoptosis and phagocytosis rate were both effectively induced and peaked at 12 h post the treatment of rCgTNF-1 with the concentration of 100 ng mL−1 (23.3 ± 3%, P < 0.01), 50 ng mL−1 (5.3 ± 0.6%, P < 0.05) and 10 ng mL−1 (6.7 ± 1.2%, P < 0.05), respectively. After the co-stimulation of LPS and rCgTNF-1, the apoptosis and phagocytosis rate of oyster haemocytes, and the activities of PO and lysozyme in the haemolymph all increased significantly, and reached the peak at 12 h (apoptosis rate 26.7 ± 1.5%, P < 0.01), 12 h (phagocytosis rate 8.3 ± 0.6%, P < 0.01), 6 h (PO 1.11 ± 0.01 U mg prot−1, P < 0.01) and 12 h (lysozyme 168.9 ± 8.3 U mg prot−1, P < 0.05), respectively, which were significantly higher than that in the LPS group. Furthermore, the anti-bacteria activity in the LPS + TNF group was significantly higher than that in the LPS group during 6-12 h. All the results collectively indicated that CgTNF-1 was involved in the oyster immunity and played a crucial role in the modulation of immune response including apoptosis and phagocytosis of haemocytes, and regulation of anti-bacterial activity as well as the activation of immune relevant enzymes.