Molecular characterization and expression of porcine Siglec-5

• Generation of cell lines expressing porcine Siglec-5.
• Development of monoclonal antibodies to porcine Siglec-5.
• Porcine Siglec-5 is expressed on myeloid cells and their precursors, and at low levels on plasmacytoid dendritic cells.

In this study we describe the characterization of the porcine orthologue of Siglec-5. A cDNa clone was obtained from a porcine cDNa library derived from swine small intestine which encodes a 555 a-a type 1 transmembrane protein with sequence homology to human Siglec-5. This protein consists of four Ig-like domains, a transmembrane region, and a cytoplasmic tail with two tyrosine-based signalling motifs. When expressed as a recombinant protein fused to the Fc region of human IgG1, porcine Siglec-5 was able to bind porcine red blood cells in a sialic acid-dependent manner. Monoclonal antibodies (mAb) were developed against porcine Siglec-5 and used to analyse its expression in bone marrow and blood cells, and lymphoid tissues. Porcine Siglec-5 expression was mainly restricted to myelomonocytic cells and their precursors, being detected also, although at low levels, on plasmacytoid dendritic cells and B lymphocytes. In lymphoid tissues, ellipsoids of the spleen and subcapsular and medullar sinuses of lymph nodes were positive for Siglec-5. These mAbs were able to precipitate, from granulocyte lysates, a protein of approximately 85 kDa under non-reducing conditions, indicating that porcine Siglec-5 is expressed as a monomer in the plasma membrane.