The murine B7-2 (mB7-2) costimulatory molecule is expressed on APCs early during the course of an immune response, suggesting that it may play a pivotal role in the decision between T cell activation and anergy. Murine B7-2 mRNA displays a restricted pattern of expression; it is inducible in B cells, T cells, NK cells, and dendritic cells, but constitutively expressed in unstimulated monocytes. The constitutive and inducible expression of mB7-2 on distinct cell types indicates that mB7-2 is regulated differentially. To further characterize mB7-2 transcripts, we employed 5' rapid amplification of cDNA ends and reverse transcriptase-PCR to examine transcripts expressed in a variety of types of APCs and analyzed the genomic organization of the mB7-2 gene. We report here that the mB7-2 locus consists of 12 exons and demonstrate that exons 1 through 5 can be used in alternative fashions to produce five distinct transcripts, differing in their 5' untranslated and signal regions. The expression of these transcripts differs in distinct types of APCs and is modulated by stimuli that activate B cells. These results demonstrate that mB7-2 transcripts are differentially regulated in a tissue-specific fashion and in response to activation stimuli.