LAMP3/CD208 is a member of the lysosomal-associated membrane protein family and is used as a putative marker for mature dendritic cells (DCs) in humans since it is upregulated upon DC activation and maturation. This paper reports the cloning and sequencing of LAMP3 in rainbow trout. The predicted trout LAMP3 shares the characteristic features of LAMP family members such as a C-terminal lysosomal sorting motif (G-Y-D-R-I) in the short C-terminal cytoplasmic tail, typical for lysosomal targeting, four potential N-linked glycosylation sites (NXS/T), four conserved cysteines in the membrane-proximal domain and the luminal domain divided by a serine/proline-rich region. Expression studies revealed that trout LAMP3, like chicken LAMP3, was constitutively expressed in a wide range of lymphoid tissues, at highest levels in the head kidney, liver and spleen, respectively. LAMP3 was also constitutively expressed in trout head kidney macrophages and RTS11 cells and the expression was shown to be induced in vivo after infection with viral and bacterial pathogens and in cultured macrophages after modulation with microbial mimics (LPS and PolyIC). Thus, it is clear that if LAMP3 is expressed by trout DCs it is not exclusively expressed by them. However, the marker is valuable to further study antigen presentation in fish and to complement already known DC markers. (c) 2012 Elsevier Ltd. All rights reserved.