Cellular localisation of tumour antigen (TA-4) in normal, dysplastic and neoplastic squamous epithelia of the upper aerodigestive tract.

We report the use of tumour antigen (TA-4) polyclonal antiserum to assess the level and pattern of TA-4 antigen expression in formalin-fixed paraffin-embedded tissue sections from 110 patients with a range of normal, dysplastic and malignant squamous epithelia from various sites in the upper aerodigestive tract. There was a high degree of TA-4 antigen expression in the superficial layers of normal squamous epithelium and in well-differentiated squamous cell cancers (SCC). TA-4 expression was consistently absent in dysplastic oral squamous epithelium and in poorly differentiated SCCs. The degree of cellular heterogeneity in moderately differentiated SCCs was such that morphologically identical squamous cancer cells could be distinguished on the basis of TA-4 expression. Immuno-electron microscopy localised TA-4 antigen to tonofibrils in both normal buccal (squamous) cells and in squamous cancer cells. Results of Western blotting confirmed the presence of a 48 kDa protein consistent with TA-4 antigen in both SCCs and in normal buccal mucosa. We conclude that TA-4 protein is a normal cellular component, that cellular TA-4 expression is related to the level of cellular differentiation in squamous epithelia and that it is not likely to be useful as an independent index of cellular proliferation or malignant behaviour.