Cre-mediated excision of the parental Fkbpltm1(KOMP)Wtsi allele resulted in the removal of the neomycin selection cassette and exon 2 leaving behind the inserted lacZ reporter sequence. Further information on targeting strategies used for this and other IKMC alleles can be found at http://www.informatics.jax.org/mgihome/nomen/IKMC_schematics.shtml. Real-time quantitative PCR analysis revealed a ~2-fold reduction of mRNA expression in spleen tissue lysates from heterozygous mutant mice; however, serum protein levels were downregulated up to 4-fold relative to wild-type controls.