To date, the mechanisms of inflammation have been poorly studied in fish of 
commercial interest, due to the lack of development of appropriate experimental 
models. The current study evaluated a local inflammation triggered by a 
polymeric carrageenin mixture (a mucopolysaccharide derived from the red seaweed 
Chondrus crispus) in the skin of gilthead seabream (Sparus aurata). Fish were 
injected subcutaneously with phosphate-buffered saline (as control) or 
λ/κ-carrageenin (1%), and skin samples from the injection sites were collected 
1.5, 3 and 6 hr post-injection, processed for inclusion in paraplast and stained 
with haematoxylin-eosin, Alcian blue or periodic acid-Schiff. Furthermore, 
immunohistochemistry and expression analyses of several cells' markers and 
proinflammatory genes were also analysed in samples of the injected sites. 
Microscopic results indicated an increased number of skin mucus-secreting cells 
and acidophilic granulocytes in the skin of fish studied at 1.5 hr and 3 hr 
post-injection with carrageenin, respectively, with respect to the data obtained 
in control fish. Otherwise, both the gene expression of the non-specific 
cytotoxic cell marker (granzyme B, grb) and the proinflammatory cytokine 
(interleukin-1β, il-1β) were up-regulated at 1.5 hr in the skin of fish injected 
with carrageenin compared with the control fish, whilst the gene expression of 
acidophilic granulocyte markers (NADPH oxidase subunit Phox22 and Phox40, phox22 
and phox40) was up-regulated at 3 and 6 hr in the carrageenin group, compared 
with the control group. In addition, the gene expression of myeloperoxidase 
(mpo) was also up-regulated at 6 hr in the skin of fish injected with 
carrageenin in comparison with control samples. The present results indicate the 
chronological participation of two important immune cells involved in the 
resolution of the inflammation in the skin of gilthead seabream.