A new specific method for measuring S-100B in serum.

The S-100 family of proteins are acidic calcium and zinc binding low molecular weight proteins mainly present in astrocytes and in a population of oligodendrocytes of the CNS. S100b, an acidic low weight and zinc binding protein, has attracted considerable interest due to its release into the cerebrospinal fluid and blood from brain tissue following brain damage and from malignant melanomas. A new simple two-step incubation assay has now been elaborated in which two catcher and one tracer monoclonal antibodies are used. The specificity of this assay is high because all the MAbs used bind exclusively to S-100B, as shown by real-time biospecific interaction analyses. Moreover, the working range of the assay is 0.2-60 micrograms/L with a CV of less than 10%; the resulting high sensitivity has been confirmed by clinical studies. Time dependence, shaking conditions, lower limit of detection limits, effects of dilution, hook effect, recovery, impression as intra- and interassay variations, and crossreactivities with S-100A1 were tested in order to obtain a highly reproducible assay. Sera from healthy blood donors and patients undergoing cardiopulmonary bypass operations were tested with the assay. Several of the patients undergoing open heart surgery presented measurable values in this IRMA S-100 assay, indicating cerebral effects of open heart surgery. The test may be used for postoperative monitoring of these patients.