Inactivation of the b7-h2 gene locus. (A) Partial restriction map of the wild-type b7-h2 locus, the targeting construct, and the inactivated locus after homologous recombination (restriction enzymes: B indicates BamHI; E, EcoRI; H, HindIII; N, NcoI; S, SalI). Exons coding for the different domains of the B7-H2 protein (Cyto indicates cytoplasmic tail; Tm, transmembrane; C, Ig constant region–like; V, Ig variable region–like; SP, signal peptide) are indicated together with the external probe used to screen ES cells and mice, which distinguishes the 2.8-kb wild-type and 1.7-kb targeted loci. (B) Southern blot analysis of EcoRI-digested liver DNA from wild-type (+/+), heterozygous (+/–), and homozygous (–/–) B7-H2 knockout mice using the external probe. (C) Northern blot analysis using full-length B7-H2 cDNA as probe of splenic RNA prepared from wild-type, heterozygous, and homozygous B7-H2 knockout mice. (D) Flow cytometry analysis of surface B7-H2 expression on splenocytes of wild-type (top panel) and B7-H2^–/– (bottom panel) mice gated on CD19⁺CD3^– cells. The thin line indicates cells that were stained with the isotype-matched control antibody, while the bold line indicates cells that were stained with the PE-conjugated anti–B7-H2 antibody. Vertical line indicates mean fluorescence intensity (MFI).