The application of a monoclonal antibody to CD62L on paraffin-embedded tissue samples in the assessment of the cutaneous T-cell infiltrates

Background:  A reduction in the expression of the pan T-cell markers CD7 and CD62L supports an endogenous T-cell dyscrasia. Previously, clone availability for CD62L restricted its application to frozen tissue sections. Materials and methods:  A nonavidin/biotin technique to examine CD3, CD62L, and CD7 in paraffin formalin-fixed tissue in non-neoplastic and neoplastic T-cell infiltrates. Results:  In the reactive group, CD62L manifested a 15 and 22% reduction in epidermal and dermal staining, respectively; there was a 42 and 31% reduction in epidermal and dermal CD7 staining. In lymphomatoid hypersensitivity, CD62L showed a 24 and 9% reduction in epidermal and dermal staining, respectively; CD7 staining demonstrated reduced staining by 70 and 66% in the epidermis and dermis. In the non-lymphomatous endogenous T-cell dyscrasia and lymphoma categories, an 80% diminution in CD62L and CD7 expression was seen. Conclusions:  CD62L can be successfully applied in formalin-fixed tissue and exhibits enhanced specificity compared to CD7 in the evaluation of cutaneous T-cell infiltrates. Both CD62L and CD7 in paraffin-embedded, formalin-fixed tissue are useful diagnostic adjuncts, especially in regard to the discrimination of lymphomatoid hypersensitivity reactions from true endogenous T-cell dyscrasia.