Cloning, expression, and function of BLAME, a novel member of the CD2 family

The CD2 family is a growing family of Ig domain-containing cell surface pro teins involved in lymphocyte activation. Here we describe the cloning and e xpression analysis of a novel member of this family, B lymphocyte activator macrophage expressed (BLAME). BLAME shares the structural features of the CD2 family containing an IgV and IgC2 domain and clusters with the other fa mily members on chromosome 1q21. Quantitative PCR and Northern blot analysi s show BLAME to be expressed in lymphoid tissue and, more specifically, in some populations of professional APCs, activated monocytes, and DCs. Retrov iral forced expression of BLAME in hematopoietic cells of transplanted mice showed an increase in BI cells in the peripheral blood, spleen, lymph node s, and, most strikingly, in the peritoneal cavity. These cells do not expre ss CD5 and are CD23(low)Mac1(low), characteristics of the B1b subset. BLAME may therefore play a role in B lineage commitment and/or modulation of sig nal through the B cell receptor.