Application of monoclonal antibodies in a sandwich enzyme-linked immunosorbent assay for identification and detection of soluble human B and T lymphocyte attenuator.

B and T lymphocyte attenuator (BTLA) is recently identified as the third co-inhibitory receptor with similarities to CTLA-4 and PD-1. Previous reports have shown that BTLA is associated with autoimmune diseases, viral infections and tumor immune evasion. However, the possibility of the existence and role of a soluble form of human BTLA (sBTLA) has not been revealed. Based on our previously generated mouse anti-BTLA monoclonal antibodies, we intend here to develop a novel enzyme-linked immunosorbent assay (ELISA) for detecting sBTLA. Using monoclonal (MAb) 8H9 as coated antibody and the biotin-labeled MAb 7D7 for detection, a sandwich ELISA was developed with good sensibility, line reliability, and specificity. With the established ELISA, the existence and concentration of sBTLA were demonstrated for the first time. It was found that soluble sBTLA existed in the sera of healthy donors and the quantitation of sBTLA climbed along with increasing age, indicating sBTLA may be correlated with immune dysregulation resulting from the aging. Hence, a sandwich ELISA for detecting sBTLA was successfully established and soluble BTLA existing in human serum was first identified, which might play an important role in immunoregulation.