In vitro effects of arachidonic acid on immune functions of head kidney macrophages isolated from large yellow croaker (Larmichthys crocea)

The experiments were conducted to determine the effects of arachidonic acid (ARA) on macrophages isolated from large yellow croaker head kidney. After exposing to serum-free medium for 1 day, cultured cells were incubated in medium supplemented with graded levels of ARA (0, 5, 25, 100, 200 and 1000 μM) in the form of fatty acid bovine serum albumin (FA-BSA) complex for 12 h, 24 h and 36 h, respectively. Cells treated with 0 μM ARA (2% bovine serum albumin, BSA) were included as control at each incubation time. Following stimulation, cell viability, lipid peroxidation, secretory phopholipase A2 (sPLA2) production and some immune parameters including phagocytosis, respiratory burst activity, prostaglandin E2 (PGE2) and Interleukin 1β (IL-1β) production were examined. Results showed that cell viability decreased with prolonged exposure and increasing ARA concentration. Especially after 36 h, cell viability was significantly decreased by incubation with higher levels of ARA (200 and 1000 μM) (P < 0.01). In the meanwhile, higher levels of ARA (200 and 1000 μM) caused a significant increase in the production of malondialdehyde (MDA) (P < 0.05, P < 0.01). Phagocytosis percentage (PP) values were significantly higher in treatments with 25 and 100 μM ARA (P < 0.05), but significantly lower in treatments with 1000 μM ARA compared to the control group (P < 0.01). Enhanced intracellular superoxide anion (O2−) synthesis was found in cells treated with each level of ARA with an exception of 1000 μM ARA (P > 0.05). The significantly promoted production of sPLA2 seemed to be irrelevant to increased ARA concentration, while PGE2 production was significantly increased in an ARA dose dependent way (P < 0.01). No pronounced effect on IL-1β production was observed between the control and ARA group, and levels of IL-1β in cell culture supernatant were fairly low (only approximately 6 pg/ml). These findings suggested that ARA could influence the immunity and physiological conditions of macrophages from head kidney of large yellow croaker in vitro.

► Primary cultured cell model could be used for immunity-related researches on fish.
► High levels of ARA significantly lowered cell viability and elevated MDA production.
► Optimal levels of ARA exerted positive effects on immunity of fish macrophage.
► Inhibitory effects of high levels of ARA on cell immunity were due to cytotoxicity.