Exon 1 sequences repress CD85j expression. Human PBMCs were transfected with expression constructs containing variousLILRB1 cDNAs and/or GFP. CD85j and GFP expression in CD4 T cells was analyzed 24 hours after transfection by flow cytometry. (A) Histograms and bar graph comparing CD85j expression by full-length (BC015731) cDNA, 5′-UTR plus coding region, and coding region alone. Results are representative of 6 experiments. MFI indicates mean fluorescence intensity. (B) Histograms and bar graph comparing various portions of the LILRB1 5′-UTR plus coding region and coding region alone. Δex1(AF84) and Δex1(AF85) contain the LILRB1 5′-UTR from AF283984 and AF283985 sequences, respectively. Δex1Δex2 begins with exon 3 and continues through the LILRB1 coding region. (C-F) A plasmid expressing GFP was cotransfected along with a LILRB1 5′-UTR plus coding region or coding region alone plasmid. Results are representative of 6 experiments. (C) Representative histograms showing CD85j and GFP expression in cotransfected CD4 T cells. (D) Flow cytometry plot of samples shown in panel C. (E) Graph of the percentage of CD85j⁺ CD4 T cells in cells cotransfected with GFP. Samples were divided into quintiles based on GFP expression, and means + SDs from 3 transfections were calculated for each quintile. (F) Relative LILRB1 mRNA (exon 8) in cotransfected cells. cDNA was treated with DpnI before real-time PCR to digest plasmid DNA; n = 3 transfections. (G) LILRB1 5′-UTR sequences that include (BC015731) or exclude (AF283985) exon 1 were cloned upstream of the GFP ORF of pmaxGFP. Data showing GFP MFI relative to an unaltered GFP control vector are presented as mean + SD from 3 transfections.