Purification of human alpha-1-fetoprotein by ammonium sulphate gradient solubilization: development of reagents for radioimmunoassay

Comparative studies of Iodo-bead and chloramine-T methods for the radioiodination of human alpha-fetoprotein

Human alpha-fetoprotein (h-AFP) of iodination grade was radiolabeled with Na125I by chloramine-T (conventional method) and by Iodo-bead (solid-phase method) in our laboratory under standard and varied conditions, such as quantity of h-AFP and volume of the reaction mixture. We have slightly modified the chloramine-T method and developed a protocol for the Iodo-bead method of iodination. Our results show that while the chloramine-T method yields radiolabeled h-AFP of apparently 40% higher specific radioactivity (SR) than those of the Iodo-bead method, the latter appears to be a simpler, more controllable and milder method, giving rise to a more stable population of [125I]h-AFP. This is supported by the results of radioactive counting of [125I]h-AFP collected from a Sephadex G-50 column after radioiodination, storage stability and immunoreactivity with anti-h-AFP.

Comparison of two immunoassay methods for the determination of alpha-fetoprotein in amniotic fluid

We compared two immunoassay methods for determination of alpha-fetoprotein in amniotic fluid. The two methods showed a very good correlation and this is further confirmed by the clinical study. The electroimmunoassay (rocket immunoelectrophoresis) seems suitable for a small laboratory, whereas radioimmunoassay may be a better choice for a large laboratory.

Studies of an alpha-fetoprotein assay using dry blood-spot samples to be used for the detection of fetal neural tube defects

We modified the Pharmacia serum alpha-fetoprotein (AFP) kit to enable its use with dry blood-spots on filter paper. Reference values were established for blood from 253 women in the 16th to 18th weeks of gestation. The result by the present technique in a woman with a confirmed anencephalic fetus was elevated, and in agreement with the results of AFP assays in serum and amniotic fluid. Blood AFP was stable on dried filter paper sent by mail.

Heterogeneity of pregnancy-specific beta 1-glycoprotein following purification from maternal serum and partial characterization of a high-molecular-weight component

Pregnancy-Specific beta 1-Glycoprotein (PSB1G) has been purified from maternal serum by physico-chemical and immunochemical methods. Marked instability of the protein was noted after partial purification which correlated with hydroxylapatite chromatography of PSB1G. Three molecular heterogeneous forms were demonstrated by gel filtration on Sephacryl S-200 which were designated as PSB1G-I, II and III. Each of the latter purified materials displayed altered immunoelectrophoretic mobility, i.e., altered from beta 1 to gamma mobility. In immunodiffusion experiments PSB1G-I reacted in complete immunological identity with 'native' serum PSB1G whereas PSB1G-II and III reacted in partial identity with each of the latter, suggesting that they are dissociation and/or degradation products of the parent PSB1G. The apparent molecular weights of PSB1G-I, II and III as determined by gel filtration were 280 000, 69 000 and 23 000, respectively, PSB1G-I was selected for structural analysis on the basis of its immunological identity with 'native' antigen. SDS-PAGE studies of PSB1G-I with and without reducing agent strongly suggest that PSB1G-I and 'native' serum antigen are composed of two dissimilar subunits of equal molecular size which are bonded together by non-covalent linkage. One of the subunits appears to represent a single polypeptide chain, whereas the other subunit appears to be composed of two polypeptide chains of unequal size that are linked together by covalent bonds. Investigations are continuing towards confirmation of the proposed structural model of PSB1G-I by an alternate methodology of protein structure analysis.

Development of a provisional reference human cord serum standard for alpha-fetoprotein determination

A lyophilized human cord serum secondary reference standard (988 vials of 1 mL/vial) has been prepared at the Laboratory Centre for Disease Control (L.C.D.C.) in Ottawa to assist in the standardization of AFP determinations. HBSAG-negative lots of cord serum were used to prepare the standard. The moisture content of the freeze-dried material was less than 0.5 percent. AFP mass calibration standards were prepared by direct weighing in duplicate of highly purified freeze-dried material. Two RIA calibration runs were conducted on the reference cord serum employing the WHO First International Standard for AFP (72/225) and L.C.D.C. mass standards. Parallelism of dose response curves within assays was demonstrated between reference cord serum and mass standards and between the latter and the WHO standard. The mean WHO kIU of AFP per vial of reference serum (+/- coefficient of variation) was 63.0 +/- 6.4 and the mean mass of AFP determined as micrograms per vial was 80.7 +/- 7.9. A small-scale (pilot) interlaboratory calibration of the reference cord serum in mass units resulted in heterogeneous AFP estimates which ranged from 54.4 to 80.7 micrograms/vial. Greater uniformity of the latter results was noted following conversion of the mass estimates to WHO international units conversion factors provided by several laboratories.