In Vitro Effects of Lipopolysaccharide and Stress Hormones on Phagocytosis and Nitric Oxide Production by Enriched Head Kidney Macrophage Cultures in the Catfish

Abstract

Head kidney (HK) is the embryonic pronephric kidney retained in adult teleosts and contains the adrenal homologues (interrenal and chromaffin cells) and hemopoietic tissue. The adrenal homologues secrete the stress hormones glucorticoids (cortisol) and catecholamines, and the hemopoietic tissue is a major source of monocytes/macrophages and neutrophils that serve as the first line of defence against invading pathogens. In the present study, head kidney macrophage-enriched preparations of Heteropneustes fossilis were used to demonstrate the dynamics of phagocytosis and nitric oxide (NO) production in the presence of lipopolysaccharide (LPS; bacterial toxin), the synthetic glucocorticoid dexamethasone and/or catecholamines. The incubation of enriched macrophage cultures with LPS for 6 h at 20 o C stimulated phagocytosis of yeast cells and fluorescent latex beads. On the other hand, the cortisol agonist dexamethasone (10 nM) inhibited phagocytosis of yeast cells and latex beads under similar conditions. LPS stimulated inducible NO synthase (iNOS)-like expression in the macrophage cultures, which was inhibited by dexamethasone in co-incubations. Complementary to the iNOS expression, LPS stimulated NO production (nitrite level), which was inhibited by the NO synthase inhibitor L-NMMA. Dexamethasone inhibited basal as well as the LPS-induced stimulation of NO. The catecholamines epinephrine and norepinephrine did not alter the basal NO level but inhibited the LPS-induced stimulation of NO. Dopamine stimulated NO production only at a higher concentration. The results provide evidence for the existence of an endocrine-immune interaction at the level of the head kidney to modulate macrophage activity and immune functions in the catfish.