Levamisole activates several innate immune factors in Scophthalmus maximus (L.) (Teleostei)

Levamisole, originally synthesized as an anti-helminthic, has been widely used in human and veterinary medicine as an immunomodulator or adjuvant. However, data on its use in fish are scarce, and no information is available for turbot. To study the effects of levamisole treatment on the innate immune system of juvenile turbot, two different doses (D1=500 mg/kg; D2=250 mg/kg dry food) were orally administered for 2 weeks and samplings were performed at -10, 14, 28, 49 and 77 days post treatment (p.t.). Biometrical, haematological, histological and immunological data were obtained. Specific growth rate was higher in the medicated groups than in the control (C), but the difference was statistically significant only for D1 fish at day 49 p.t. The leucocytes/trombocytes ratio was significantly higher in D1 than in C fish at 14 days p.t., but decreased subsequently. At most samplings, the percentage of the circulating lymphocytes was lower and that of the progranulocytes was higher in the medicated fish than in the C ones. The percentage of fish with high haemotopoietic activity in the kidney was clearly higher in D1 and D2 fish than in C ones at some sampling points. The respiratory burst activity of blood leucocytes was significantly higher in D1 fish than in C ones in all samplings, except at day 77 p.t. when control fish experienced a rebound effect. In all medicated fish, an initial increase of such activity was observed, followed by a further decrease. Their serum peroxidases followed a contrary pattern, with a decrease in the second sampling and a subsequent and non-significant recovery, a situation also observed for serum lysozyme and complement. Therefore, oral levamisole treatment actually affects some turbot immune factors, although stimulation or depression can occur depending on the considered factor and the administered dose. These results point out the,interest of further studies on the mechanisms involved in the levamisole action for its adequate use as immunomodulator.