Measurement of SP1 in samples with varying SP1α:SP1β ratios

Mixtures containing a fixed amount of SP1α, increasing amounts of SP1β and vice versa have been measured by rocket immunoelectrophoresis, by enzyme immunoassay and by radioimmunoassay. Both proteins have immunological determinants which react with standard antisera to SP1 and the value obtained for any particular mixture is dependent on the ratio of the proteins. The effect of the ratio on measurement by immunoelectrophoresis is different from that on measurement by enzyme immunoassay or radioimmunoassay. As these two proteins exist together in the blood of pregnant women, results obtained by the two types of assay cannot be compared. Even with the same method the results will depend on the ratio which varies from subject to subject. It is concluded that until specific measurements for SP1α and SP1β are designed, clinical application studies must be viewed with reserve. (Auth.)