NO in the developing gut of Dicentrarchus labrax: an early immune role ?

It is known that nitric oxide (NO) plays an important role in the immune-neuroendocrine communications. In this issue, we have examined the appearance and distribution of nitric oxide sinthase (NOS) histochemically, immunohistochemically and biochemically during development of the sea bass gut. In 4 and 24-day-old larvae the NOS activity evaluated by NADPH-diaphorase was strong in all epithelial cells and in cell and fibers of intestinal wall, at all gut levels. In the same larval stages and localizations immunoreactive material to antibodies against nNOS and iNOS was present. In the 5-month-old adult gut both enzimatic activity for NADPH-diaphorase and immunoreactivity (IR) to anti-nNOS disappeared from epithelium remaining in the gastro-enteric nervous system. The IR to anti-iNOS completely disappeared. Western blot analysis showed that neuronal (about 150,000 mol. wt band) and inducible (about 135,000 mol wt band) NOS-immunoreactive proteins are present in 24 day-old larvae gut. In the 5 month-old adult gut nNOS and iNOS IR disappeared in the soluble fraction of crude gut homogenates. A small amount of nNOS IR was present in particulate gut fraction. Our data show that both the calcium-calmodulin dependent nNOS and calcium-independent iNOS are present in the larval gut of sea bass. In this species the maturation of cell-mediated immune responses and humoral immune system takes place respectively around the first and second month post hatching (Scapigliati et al., 2002). The presence of inducible NOS in the same regions of the sea bass gut in which the GALT will differentiate, may suggest for NO a role in early defence mechanisms, before of establishment of immune responses in GALT.