Occurrence in the Placenta and in Other Human Tissues

The development of more sensitive radio- and enzymimmunoassays led to the discovery that SP₁ should not be considered pregnancy specific similarly, the best known pregnancy hormone, Human Chorionic Gonadotropin, was found to be not truly specific to pregnancy or the placenta in that it is detectable in concentrations of a few pg/1 in healthy nonpregnant humans, male and female alike. The obstructive effect of nonspecific staining was eliminated by parallel IgG staining, with which the protein attachment could be easily differentiated in the control samples. With this procedure, N. V. Engelhardt et al obtained better distinction between specific and nonspecific fluorescence in the various tissue sections. The occurrence of PP₁₇ in concentrated extracts of human tissues was studied by Ouchterlony’s gel-diffusion test; PP₁₇ was not observable in any fetal or adult organ extract analysed.