Identification of ILT5 as target antigen by eukaryotic expression cloning. (A) Screening of a DC library expressed in Bw cells with serum G106/1. (Top panel) Bw cells expressing the cDNA library derived from DCs were incubated with serum G106/1 (final concentration 1:200) and bound antibodies were detected by PE-labeled antihuman IgG antibodies. PE-positive cells were gated for sorting. (Bottom panel) Serum G106/1 was incubated with the cell pool obtained after 2 rounds of sorting (gray histogram) or with control Bw cells (open histogram). (B) PCR recovery of the retroviral cDNA inserts from single-cell clones reacting with serum G106/1. Retroviral cDNAs were recovered from the genomic DNA of reactive clones by PCR. A 3.6-kb band was present in the PCR products of all clones. (C) The 3.6-kb cDNA encodes an antigen recognized by G106/1. Serum G106/1 reacts with Bw cells transduced to express a 3.6-kb cDNA (gray histogram) but not control-transduced Bw cells (open histogram).