Temperature-dependent immunoreactive assay to screen for digoxin-like immunoreactive factor(s).
Endogenous circulating digoxin-like immunoreactive factors (DLIF) are known to cross-react with antibodies to digoxin and to inhibit Na+/K(+)-transporting ATPase (Na+K+ATPase; EC 3.6.1.37). Moreover, increasing the immunoassay temperature from 4 to 37 degrees C markedly decreases DLIF from human cord serum. We tested several compounds, including hormonal steroids, bile salts, lipids, and methionine-enkephalin, for their ability to cross-react with two commercially available 125I digoxin RIAs, to inhibit porcine Na+K+ATPase, and to see whether they present the same incubation temperature dependence as human cord serum. Except for methionine-enkephalin, all compounds were inhibitors of Na+K+ATPase in the range of 1-10 mmol/L. Progesterone exhibited the highest cross-reactivity in the two RIAs. The apparent digoxin immunoreactivity for the majority of the cross-reacting steroids, bile salts, and linoleic acid was markedly decreased by increasing the incubation temperature from 4 to 37 degrees C, whereas estriol, pregnanediol, and nonspecific compounds (e.g., ethanol, human serum albumin) did not appear to be temperature-sensitive. Both lysophosphatidyl lipids gave an increased apparent digoxin concentration with increasing incubation temperature. Our data suggest that numerous weakly cross-reactive compounds can parallel the response of human cord serum. However, the temperature-dependent effect could be an additional criterion for identifying DLIF.
Guédeney
X
X
INSERM Unité 26, Hôpital Fernand Widal, Paris, France.
Chanez
C
C
Grenier
A
A
Scherrmann
J M
JM
D000906:Antibodies / Q000276:immunology; D000918:Antibody Specificity; D001798:Blood Proteins / Q000032:analysis* / Q000276:immunology / Q000494:pharmacology; D002298:Cardenolides; D004076:Digoxigenin / Q000276:immunology / Q000494:pharmacology; D004077:Digoxin / Q000276:immunology; D000939:Epitopes / Q000276:immunology; D005312:Fetal Blood / Q000737:chemistry; D006801:Humans; D011374:Progesterone / Q000276:immunology; D011863:Radioimmunoassay; D012503:Saponins; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors; D013696:Temperature
D000906:Antibodies; D001798:Blood Proteins; D002298:Cardenolides; D000939:Epitopes; D012503:Saponins; C034504:digoxin-like factors; D011374:Progesterone; D004077:Digoxin; D000254:Sodium-Potassium-Exchanging ATPase; D004076:Digoxigenin