A sensitive enzyme immunoassay for the quantitation of human C5a/C5a(desArg) anaphylatoxin using a monoclonal antibody with specificity for a neoepitope.

The direct quantitation of C5a/C5a(desArg) in human plasma was achieved by a specific and highly sensitive ELISA which is based on the neoepitope-specific monoclonal antibody C17/5. The error-prone removal of C5 from plasma prior to the assay is therefore not required. With a detection limit of 20 pg C5a/ml plasma, the sensitivity of this assay allowed to define normal ranges (1.94 +/- 1.49 ng C5a/nl, mean +/- SD) of C5a/C5a(desArg) in human blood plasma. This assay will also be applicable to the quantitation of C5a in specimens with low protein content where precipitation-based assays fail to accurately determine C5a. In addition, the mAb C17/5 turned out to efficiently block the binding of C5a/C5a (desArg) to its cellular receptor and therefore provides a valuable tool in the delineation of C5a effects in complex biologic systems in the presence of native C5, such as under in vivo conditions.