Selective expression of the murine homologue of the G-protein-coupled receptor BLR1 in B cell differentiation, B cell neoplasia and defined areas of the cerebellum.

The Burkitt's lymphoma receptor 1 (BLR1) identified initially in Burkitt lymphoma cells has been the first member of the superfamily of G-protein-coupled receptors with a lymphocyte specific expression pattern. BLR1 shows significant relationship to receptors for chemokines (IL-8, MIP-1 beta) and neuropeptides. The gene encoding the murine homologue of the human BLR1 receptor was isolated and used to study its tissue-specific expression. Blr-1 consists of two exons encoding a protein of 374 amino acid residues which shows 83% identity with the human homologue. Screening of normal tissues of adult BALB/c mice revealed that blr-1-specific RNA is detected consistently at low levels in secondary lymphatic organs. The blr-1 gene is expressed regularly and strongly in lymphomas of mature B cells but not in plasmacytomas. SCID mice deficient in the development of mature B cells have strongly reduced levels of blr-1-specific RNA in the spleen. Cytokine mediated induction (IL4, IL6) of terminal differentiation of resting B cells towards Ig-secreting plasma cells completely downregulates expression of blr-1. RNA in situ hybridization using brain sections demonstrates blr 1 transcription in the granule and Purkinje cell layer of the cerebellum. The precise delineation of the restricted expression pattern of the blr-1 gene will support the identification of its ligand and may provide a clue to understand how BLR1 exerts its biological function within the immune and nervous system.