Identification and expression modulation of a C-type lectin domain family 4 homologue that is highly expressed in monocytes/macrophages in rainbow trout (Oncorhynchus mykiss)

• Cloned a rainbow trout C-type lectin we term CLEC4T1.
• We show it is expressed in immune tissues at the transcript and protein level.
• We show that LPS but not polyI:C can up-regulate this gene.
• We have generated a polyclonal antibody to trout CLEC4T1.
• We show by FACS analysis that the number CLEC4T1+ cells increase following exposure to rIL-4/13A ± LPS.

The C-type lectin domain containing (CLEC) receptors including CD209 are expressed in vivo by monocytes, monocyte-derived macrophages and dendritic cells and by in vitro generated monocyte-derived cells. This paper reports the cloning and sequencing of a lectin molecule, CLEC4T1, in rainbow trout that is a homologue of the CLEC4 family. The expression pattern of the CLEC4T1 was investigated in vivo after infection with a bacterial pathogen and in cultured macrophages after modulation with microbial mimics. Trout CLEC4T1 was highly expressed in spleen and head kidney following infection with Yersinia ruckeri. Expression could also be induced in macrophage cultures by LPS but not by Poly I:C, and suggests that the regulation of CLEC4T1 expression in trout varies according to the nature of the stimulant. A polyclonal CLEC4T1 antibody was generated and validated by Western blotting for use in evaluation of CLEC4T1+ cells by flow cytometry analysis. Freshly isolated adherent trout head kidney cultures, potentially containing macrophages and dendritic cell precursors, showed an increase of CLEC4T1+ cells (assessed by flow cytometry) upon stimulation with recombinant interleukin-4/13A. The results suggest that CLEC4T1 is a useful marker for further characterisation of monocyte derived antigen presenting cells in fish.