Immunosuppressive effect of cyclophosphamide in Nile tilapia (Oreochromis niloticus)

Cyclophosphamide, a common chemotherapeutic and immune suppressor agent, is regularly used in research to weaken the immune system in laboratory animal models. Nile tilapia (Oreochromis niloticus) is a widely used experimental fish model for immune-modulatory research; with the lack of knowledge about the immune-compromised tilapia model, an urgent need is to develop and optimise such a model. Sixty healthy Oreochromis niloticus fish, average weight 50 ± 10 g, were divided into four experimental groups. Fish in group I, negative control group, were injected with phosphate-buffered saline only, and fish in groups II, III and IV were injected with cyclophosphamide (CP) at 100, 200 and 400 mg/kg body weight (BW), respectively, via the intraperitoneal route. Different immune-related parameters were investigated 3 weeks after CP injection. The results have revealed a significant decrease in total red blood cells (RBCs), white blood cells (WBCs) and thrombocyte counts and reduced haemoglobin and haematocrit values in CP-treated fish, especially those injected with 200 mg/kg BW compared with the control group (p < 0.05). Also, significantly lower levels of serum proteins (total protein, albumin, α1- and γ-globulins) were observed in CP-treated fish, especially those injected with 200 mg/kg BW in comparison with the control group (p < 0.05). Furthermore, CP-treated fish showed a reduction in the expression of immune-related genes (interleukin-1, and tumour necrosis factor-α in spleen and tumour necrosis factor-α and transforming growth factor β-1 in head-kidney), especially those injected with 200 mg/kg BW compared with the control group (p < 0.05). In conclusion, the Oreochromis niloticus immune-suppressed model can be induced by intraperitoneal CP injection at 200 mg/kg BW.