Adaptive immunity in teleosts: cellular immunity.

Specific cell-mediated immunity in fish is to date a relatively poorly studied area in fish immunology. Despite breakthroughs in the cloning of the fish TcR and major histocompatibility (MHC) molecules, and more recently the CD3 and CD8 marker molecules, assays to measure specific T-cell responses are still in their infancy. The classical division of T cells into cytotoxic (Tc) and helper (Th) subpopulations is probably relevant to fish, based on the presence of these functional activities and MHC class I and II molecules, but as yet even this is not definitively proved. This review will consider which specific cell-mediated responses can be measured within fish and what their relevance is to fish vaccination programmes.