Leu-8 and Leu-9 antigen phenotypes: Immunologic criteria for the distinction of mycosis fungoides from cutaneous inflammation

The distinction of mycosis fungoides from reactive cutaneous inflammation can be difficult. Unfortunately, since many reactive processes exhibit predominantly a mature helper T cell phenotype similar to that expressed by most cases of mycosis fungoides, standard immunologic marker studies have not been very helpful in differential diagnosis. To determine whether novel immunophenotypic criteria could be developed that correlate with the diagnosis of cutaneous involvement by mycosis fungoides, we studied the expression of Leu-8 and Leu-9 antigens by T cells in forty-one skin biopsy specimens from twenty-seven patients with mycosis fungoides and thirty-four skin biopsy specimens from thirty-three controls with a variety of benign cutaneous diseases. These antigens are expressed by the majority of normal T cells in the blood and lymphoid tissues but are often absent in T cell lymphomas or expressed by only a minority of tumor cells. Semiquantitative grading of the percentage of Leu-8 + and Leu-9 + T cells in our patients revealed that deficiency of these antigens (i.e., expression by ⩽33% of T cells) was more prevalent among mycosis fungoides patients than among controls and became more specific for mycosis fungoides as the percentage of Leu-8+ and Leu-9+ T cells decreased. In initial biopsies, ⩽33% of T cells were Leu-8+ in 82% of mycosis fungoides patients versus 15% of controls, while ⩽10% of T cells were Leu-8+ in 52% of mycosis fungoides patients versus only 3% of controls. Similarly, ⩽33% of T cells were Leu-9+ in 59% of mycosis fungoides patients versus 3% of controls while ⩽10% of T cells were Leu-9+ in 41% of mycosis fungoides patients versus 0% of controls. Concurrent or serial biopsies obtained in eleven patients showed either phenotype stability or a trend toward development of Leu-8 or Leu-9 deficiencies over time. Deficiency of Leu-8 or Leu-9 occurred at all clinicopathologic stages of mycosis fungoides studied (la through III) and in individual lesions ranging from poikilodermatous patches to advanced tumors. In contrast, expression of Leu-8 and Leu-9 by the majority of T cells was much more common in controls than in mycosis fungoides patients (85% vs 11%). These findings indicate that major differences in cellular antigen expression exist between benign and malignant cutaneous T cell infiltrates. Furthermore, they indicate that immunophenotypic criteria may prove useful in distinguishing mycosis fungoides from cutaneous inflammation.