Silver enhancement of polymerised diaminobenzidine: increased sensitivity for immunoperoxidase staining

Unambiguous identification of lymphocytes is sometimes difficult because of weak immunostaining of the cell membrane immunoglobulins. A simple method of intensifying the diaminobenzidine (DAB) peroxidase reaction was therefore devised. Paraffin wax sections of formalin fixed tonsils and lymphomas were digested with trypsin and immunostained for kappa and lambda light immunoglobulin chains and CD3 antigen by various peroxidase linked detection systems. After reaction with hydrogen peroxide and DAB the sections were immersed in methenamine silver solution at 60 degrees C for three to seven minutes. The light brown stain on the cell membranes of the mantle zone lymphocytes became dark brown and the stronger stain of the plasma cells became black. Mantle zone B lymphocytes and CD3 positive T lymphocytes were precisely outlined even at low magnification and the lymphomas were easily classified as monoclonal or polyclonal. At high magnification, staining was clearer than with the immunogold-silver stain. Cryostat and paraffin wax sections of other tissues immunostained for various antigens showed similar intensification. Silver methenamine provides an easy means of increasing the sensitivity and visual impact of an immunoperoxidase/DAB reaction in any preparation.