Constant detection of surface and cytoplasmic immunoglobulin heavy and light chain expression in formalin-fixed and paraffin-embedded material.

The introduction of microwave detection systems has significantly enhanced the sensitivity of immunohistochemistry in formalin-fixed, paraffin-embedded tissue. The combination of protease digestion and microwave treatment including the use of heavy metal salts or urea gives an Ig heavy and light chain detection system in formalin-fixed and paraffin-embedded material as good as that achieved using fresh frozen material, with the advantage of a well-preserved morphology. The sensitivity of this method depends on the heavy metal salt used and its concentration. The use of urea yields equally sensitive results, while avoiding the toxicity of heavy metal salts. Heating times in the microwave oven also have an important influence on the results. The microwave-based technique may allow for the improved accessibility of formalin-masked antigens, as was shown here for cytoplasmic and surface immunoglobulins. It was demonstrated that formalin-fixed specimens of Burkitt's lymphoma when subjected to the new protocol almost always showed surface Ig expression, giving results comparable to those obtained in frozen sections. Moreover, it could be shown that in cases of B-chronic lymphocytic lymphoma (B-CLL) or immunocytoma, surface and cytoplasmic Ig could be detected, so that the difference may be just a quantitative one and thus may no longer be safely used as a criterion in differential diagnosis. In future, the wide use of this technique will allow for the study of Ig expression at the single cell level in morphologically well-preserved material.