Immunohistochemistry of gut-associated lymphoid tissue of the sea bassDicentrarchus labrax(L.)

Histology revealed scattered lymphoid cells at all levels of the digestive tract of the sea bassDicentrarchus labrax(L.), notably in the mucosa and sub-mucosa. Immunohistochemistry with monoclonal antibodies against T cells (DLT15) and immunoglobulin-bearing cells (DLIg3 and DLIg13) demonstrated the presence of a gut-associated lymphoid tissue. Quantitative analysis showed that the concentration of DLT15-positive cells largely exceeded that of Ig-bearing cells, while the number and the distribution of DLIg3- and DLIg13-immunoreactive cells were superimposable. An apparent gradient in the number of lymphoid cells was present, concentrating them towards the anus. This suggests that, as in other fish species, the posterior gut acquired higher immunological relevance.