Expression of fos proto-oncogene product by monoclonal antibody FO-120 in smouldering adult T-cell leukaemia (ATL).

We investigated the expression of c-fos gene product in peripheral blood mononuclear cells of patients with smouldering adult T-cell leukaemia (ATL) and healthy human T-lymphotropic virus type-I (HTLV-I) carriers by an immunofluorescence assay, using a mouse monoclonal antibody (FO-120) specific for fos gene product. Peripheral blood mononuclear cells derived from healthy HTLV-I carriers were rarely positive for FO-120, less than 2% of the cells weakly reacted with FO-120, whereas positive cells were detected in more than about 10% of cells from patients with smouldering ATL. FO-120 appears to be a useful tool for detecting smouldering ATL in asymptomatic HTLV-I infected people without using molecular techniques.