Abstract
CD27 is a member of the nerve growth factor receptor family, that includes two types of tumor necrosis factor receptor, CD40 and Fas/Apo-1. Human CD27 has been found only on lymphocytes. In T cells, its expression strongly increases in a transient fashion upon antigenic stimulation, suggesting that CD27 plays a role during T cell activation. To analyze the function of CD27, we have identified the murine CD27 at the cDNA and protein level. Murine CD27 shows an identity of 65% compared with human CD27. The amino-terminal cysteine-rich region, i.e. the putative ligand-binding domain, and the carboxy-terminal part of the cytoplasmic domain are approximately 80% identical in man and mouse. Murine CD27 has 29% identity to 4-1BB, another lymphocyte-specific member of the receptor family defined only at the cDNA level. Murine CD27 and 4-1BB have 39% homology in the cysteine-rich domain and share a conserved region in the cytoplasmic tail. Expression studies identified murine CD27 mRNA in thymus and spleen, but not in non-lymphoid tissues, while 4-1BB mRNA was not detected in any tissue tested. In resting T cells, only murine CD27 mRNA was found, while in activated T cells murine CD27 as well as 4-1BB were present at high levels. Murine CD27 and 4-1BB mRNA are expressed with different kinetics during T cell activation, suggesting that these molecules play different roles in this process. Peptide antisera identified murine CD27 as a 45-kDa protein on thymocytes and activated T cells, while 4-1BB was precipitated as a 35-40-kDa protein from activated T cells.