A highly sensitive E.L.I.S.A. for endopeptidase-24.11, the common acute-lymphoblastic-leukaemia antigen (CALLA, CD-10), applicable to material of porcine and human origin.

Endopeptidase-24.11 is a widely distributed cell-surface enzyme with a key role in the metabolism of neuropeptides. It is now known to be identical with CD-10, the common acute-lymphoblastic-leukaemia antigen (CALLA). An e.l.i.s.a. is described which utilizes two antibodies, one monoclonal, the other polyclonal, generated to pig endopeptidase-24.11. These antibodies cross-reacted with human endopeptidase-24.11, thus making the assay applicable to both species. By using optimum conditions for the e.l.i.s.a., as little as 25 pg of pure pig endopeptidase-24.11 could be quantified at 95% confidence limits. E.l.i.s.a. of tissue homogenates from a variety of pig tissues and of human kidney correlated well with enzymic assays. However, the use of detergents to solubilize the antigen greatly decreased the sensitivity of the e.l.i.s.a. The e.l.i.s.a. is 1000-fold more sensitive than the immunoradiometric assay and has advantages in specificity over enzymic assays. Daudi cells, some leukaemic cells shown to be CALLA-positive, and Caco-2 cells, could also be assayed, but N2 cavitation was necessary to fragment the cells, and only part of the total endopeptidase-24.11 activity in Daudi cells was recognized by the e.l.i.s.a.