Generation of transgenic mice expressing human FcRI. (A) Structure of the transgene consisting of a 41-kb cosmid insert carrying the gene encoding FcRI. Exons are represented by closed boxes. S1, S2, signal peptide; S3, putative additional signal exon39; EC1 and EC2, extracellular Ig-like domains; TM/C, transmembrane and cytoplasmic region; E, EcoRI; H, HindIII. (B) Southern blot analysis of hFcRI transgenic mice. Genomic DNA from transgenic (Tg) line 2107 (lane 1), line 2126 (lane 2), a nontransgenic (NTg) mouse (lane 3), and human DNA (lane 4) were digested with EcoRI and hybridized with hFcRI cDNA probe. Sizes of DNA fragments (kb) are indicated on the left. (C) Flow cytometric analysis of FcRI surface expression on mouse blood cells and peritoneal macrophages. Cells of nontransgenic (thin lines) and transgenic (bold lines) mice were stained with anti-FcRI MoAb A77-FITC. Cells were stained with Gr-1-PE or F4/80-biotin/streptavidin-PE to identify granulocytes and monocytes/macrophages, respectively. Anti-CD45/B220 and anti-TCRβ served to distinguish lymphocytes. This experiment was repeated at least five times, yielding essentially identical results. (D) Human IgA binding to transgenic neutrophils. Cells of NTg (thin line) and Tg (bold line) were incubated with human serum IgA and PE-labeled antihuman IgA antibody.