Immunoradiometric quantitation of tissue plasminogen activator-related
antigen in human plasma: crypticity phenomenon and relationship to plasma
fibrinolysis
TC Wun and A Capuano
A two-site immunoradiometric assay for tissue plasminogen activator (tPA)
antigen has been developed using immunoaffinity purified antibody. Various
treatments enhanced the detection of tPA antigen in the plasma samples.
Maximum detection was obtained by acidification of plasma to pH 4.8 to 6.5
or addition of 0.5 mol/L of L-lysine or L- arginine. Acidification or
addition of lysine to plasma is also required for maximum immunoadsorption
of plasma tPA antigen on anti-tPA- Ig-sepharose. These results indicate
that plasma tPA antigen is partially cryptic to antibody in untreated
plasma. The plasma tPA antigen isolated by immunoadsorption of either
untreated plasma or acidified plasma on anti-tPA-Ig-sepharose consists
mainly of a 100-kd plasminogen activator species as determined by
fibrin-agar zymography. The 100-kd activity is possibly a tPA:inhibitor
complex. A standardized sample preparation method was conveniently adopted
by mixing 3 vol of plasma and 1 vol of 2 mol/L of L-lysine for the assay.
Reconstitution and recovery studies showed that the method is specific and
permits full detection of both free tPA and tPA:inhibitor complex. The
validity of the assay is further supported by the finding that the
spontaneous plasma fibrinolysis previously demonstrated to be dependent on
plasma tPA antigen is correlated with tPA antigen content. Using the
standardized assay, we found that tPA antigen concentrations in 16 blood
bank plasmas are equivalent to 3.7 to 20 ng of 60 kd tPA/mL. In all the
plasma tested, more than half of the antigen is undetected unless the
plasma is treated as described above.
Volume 69,
Issue 5,
pp. 1348-1353,
05/01/1987
Copyright © 1987 by The American Society of Hematology
