NTP Update

The use of heat treatment for the removal of non-specific effects in the direct radioimmunoassay of human circulatory CEA has been widely adopted have shown the existence of heat-labile determinants on CEA which may be destroyed by this assay technique. Heat-labile antigens appeared to be shared between CEA isolated from tumour and normal colon whilst the heat-stable antigens appeared to be more tumour-associated (Rogers & Keep, 1980). The possibility was raised that antisera against heat-treated CEA might be more specific for a restricted population of CEA and possibly for cancer detection. In the present communication we report on the antigenic expression and molecular distribution of heat-labile and heat-stable epitopes on CEA. Four rabbit antisera (241-244) and a goat antiserum have been raised to heat-treated CEA (CEA heated at 85°C for 30 min in phosphate buffer at pH5) and absorbed (Rogers & Keep, 1980). These antisera gave single lines of identity on immunodiffusion against purified CEA with a reference antiserum (G61) and did not cross-react with NCA. They differ from our conventional antisera 227 and PK1G in the extent to which they recognise heat-labile components of CEA. This has been shown for antiserum 241 by double antibody radioimmunoassay (241 assay) before and after heat treatment. In separate experiments using different tumour CEA preparations, 73 and 75% of the assayable CEA were retained after heating. This contrasted with results obtained using the two conventional assays and also the Abbott EIA kit. In these cases the assay values fell by 85%, 78% and 85% respectively. Similar results were obtained for CEA extracted from normal colon. In this experiment CEA was prepared from four separate specimens treated as described above and doubling dilutions assayed. Using the 241 assay no significant change in the CEA activity occurred after heat treatment. Again this contrasted with the results of a conventional assay (227) where 65% of the activity was lost on heating. These experiments showed that antiserum 241 reacted only very weakly with heat-labile CEA as expected. Antisera to heat-treated CEA also reacted very weakly with CEA prepared from normal colon. This has previously been demonstrated with antiserum 241 by rocket electro-phoresis (Rogers & Keep, 1980) and has now been confirmed by this technique with the additional antisera raised to heat-treated CEA (Figure 1). Whereas conventional anti-CEA (PK1G) produced rockets with perchloric acid extracts of normal colon at lmgml-l (120-200ng of CEAmg-1 of extract), antisera to heat-treated …