The hybridoma technique was used to produce an allotypespecific monoclonal antibody (F11) that reacts with the products of the S, I, and D alleles of PLAP but not of the F allele. Serum and ascites samples from patients with different cancers containing high levels of PLAP were tested for reactivity with F11. These tumor-derived PLAPs were of the Nagao type as shown by their sensitivity to inhibition by l-leucine. This type of inhibition is exhibited also by the rare D allelic variant of PLAP but not by the common forms. Thus, it has been proposed that the Nagao enzyme represents reexpression of the D allele of PLAP. F11 reactive and nonreactive samples as well as samples with intermediate reactivity were found among the cancer sera and ascites. Our results show that the tumor-derived Nagao enzyme does not represent the reexpression of the D allele but instead, in spite of its distinct inhibition pattern, expresses the same genetic polymorphism that is found in the placenta.


This work was supported by Grants CA 21967 and CA 27460 from the National Cancer Institute, Department of Health and Human Services and by Swedish Medical Research Council Grant 4217.

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