CD5
surface antigen is expressed on some categories of
B cell lymphomas. The detection of CD5 coexpression on malignant B cell infiltrates, particularly in small biopsy specimens, is useful in distinguishing between
small lymphocytic lymphoma,
mantle cell lymphoma, low grade
marginal zone B cell lymphoma, and follicular small cleaved cell
lymphoma. However, conflicting results have been reported with regard to the detection of
CD5 antigen expression on B cell non-Hodgkin's
lymphomas (B-NHLs) in fixed,
paraffin embedded tissues using routine immunohistochemical (IHC) staining techniques. We used catalyzed reporter deposition (CARD) as a strategy to amplify the IHC signal and consequently increase the sensitivity of
antigen detection. CARD improved detection of
CD5 antigen without sacrificing specificity of the test. In our study, virtually all malignant B-NHLs with
CD5 antigen expression showed strong immunoreactivity for a commercially available anti-CD5
monoclonal antibody using CARD, whereas the majority of the same
lymphomas did not label for CD5 using routine IHC without CARD amplification. The concordance between
CD5 antigen detection by immunophenotyping of fresh or frozen tissues and immunostaining with CARD amplification on
paraffin fixed tissue sections was 100%. It appears that this method can be applied in the diagnostic evaluation of B-NHLs or in other situations that a weak
antigen signal is present.