A full-length cDNA of the mouse Blr1 (CXCR5) gene with a prolactin-FLAG sequence at the 5' end was cloned into the BamH1 site of plasmid p1026x containing the mouse Lck proximal promoter interrupted by the E mu heavy chain enhancer. This is transgenic line 30. Mice express mouse Blr1 on naive T cells at intermediate levels and at lower levels on B cells. (J:119641)