The majority of the
cells present in the ILT were positive for the expression of genes
coding for the CD3ε complex and CD8 co-receptors [2,5]. Those
receptors are essential for signal transduction during T cell activation. This starts with the activation of the CD3-signal transduction
complex, finishing with the proliferation and differentiation of
antigen-specific T cells [6]. Teleost CD8 T cells are typically cytotoxic
T cells, which are the principal effectors of cell mediated immune
response [6]. Furthermore, the number of Igþ cells in the ILT is very
low [2]. This indicates that the ILT most likely presents a cellmediated immune function rather than humoral. It has been suggested that immune induction could occur in the ILT, due to the
presence of scattered major histocompatibility complex class II
(MHC class II) positive cells as well as T-cell receptor [1]. A recent
study targeting the ILT of salmon infected with salmon anaemia
virus (ISAV), showed an immune response against the virus (7). Due
to the strategic position regarding antigen surveillance, and the
immune response against ISAV, it was suggested that the ILT may
have a role as a secondary lymphoid organ with clonal expansion of
IgT expressing B-cells [2,7].