Immunohistochemical localization of adenosine deaminase complexing protein in intestinal mucosa and in colorectal adenocarcinoma as a marker for tumour cell heterogeneity.

Adenosine deaminase complexing protein (ADCP), a dimeric glycoprotein, has been reported to be decreased or deficient in transformed or cancer-derived cell lines, indicating its potential significance as an indicator of malignant transformation. A similar deficiency was reported in total homogenates of tumours of colon, kidney, lung and liver. In previous biochemical studies we failed to confirm the consistent reduction in ADCP concentration in cancer tissues. A possible explanation for our findings was thought to be intercellular heterogeneity in ADCP expression in individual tumour cells. To study ADCP expression in individual cells, we developed an immunohistochemical method which was applied to tissue sections. Paraformaldehyde--lysine--periodate (PLP) solution was found to be a suitable fixative. Fixed tissue samples were paraffin-embedded, sectioned and stained for ADCP, using an indirect peroxidase-labelled antibody procedure. The protein was localized in normal colonic mucosa, mainly in the brush border region of the luminal epithelium and in cytoplasmic granules. Intense ADCP immunoreactivity was found also in the basal part of some cells. In cancer cells, three staining patterns were observed: membranous, diffuse cytoplasmic and granular cytoplasmic. The adenocarcinomas exhibited significant intratumour and intertumour heterogeneity in their staining types. Further studies on ADCP expression in colorectal cancer in relation to clinical and histopathological characteristics are warranted in order to fully evaluate the potential significance of ADCP as a cancer associated antigen.