Immunoluminometric detection of human procalcitonin

Procalcitonin is a normal precursor of the active hormone calcitonin; however, its level in blood is normally undetectable. Dramatically increased levels of procalcitonin have been found in severe systemic bacterial infections and, today, this molecule is considered to be one of the earliest inflammatory markers of sepsis. In spite of the large body of data, it is still uncertain how and from which tissues procalcitonin is released into the circulation. In our experiments, we tested the analytical performance of a flash-type chemiluminescent immunoassay. The precision and accuracy of the assay was acceptable for early detection of sepsis and procalcitonin levels showed predictive information on the outcome of the infections. Using isolated leukocyte subpopulations and acridinium-labelled anti-calcitonin monoclonal antibody, we made attempts to detect procalcitonin inside the cells or in surrounding medium by measuring the chemiluminescent signal triggered after the specific binding of the antibodies had occurred. Our preliminary data showed that lymphocytes did not contain detectable amounts of procalcitonin nor neutrophils secreted it after stimulation. However, neutrophils expressed chemiluminescence of intracellular origin. This finding suggests that neutrophil leukocytes might be a potential source of serum procalcitonin under in vivo conditions.