IDENTIFICATION OF AN ALTERNATIVELY SPLICED FORM OF THE MURINE HOMOLOGOF B7

B7 on antigen presenting cells is a costimulatory ligand necessary for full activation of T cell. Receptors for B7 have been known as CD28 o r CTLA4. We here show that in addition to B7 mRNA, an alternatively sp liced mRNA (designated as MB7-2 mRNA), that immunoglobulin (Ig)C-like domain coded by exon3 has been spliced out, is found in activated muri ne splenic B cells by reverse transcriptase-polymerase chain reaction analysis. Chinese hamster ovary (CHO) cells transfected with MB7-2 bou nd CTLA4Ig less well than those expressing B7, but bound CD28Ig to a s imilar extent, indicating that IgV-like domain contains the complete b inding site for CD28. In addition, IgC-like domain may participate in an increase in the affinity for CTLA4. Thus, MB7-2 represents a new fo rm of the murine B7 with different receptor binding properties. (C) 19 94 Academic Press, Inc.