Lymphomatoid papulosis expresses immunophenotypes associated with T cell lymphoma but not inflammation.

Twelve skin biopsy specimens of lymphomatoid papulosis from nine patients were studied immunohistologically. The large atypical cells morphologically resembled Reed-Sternberg cells in six cases and large cerebriform mononuclear cells in three cases. These cells expressed pan-T cell antigens (Leu-4 and/or Leu-5) and helper T cell antigen (Leu-3) in each case. They also expressed activation antigens: HLA (human lymphocyte antigen)-DR, HLA-DQ, Tac, and T9. Reactivity of many nuclei with Ki-67 indicated a high proliferative index. Phenotypic abnormality of the large atypical cells was evident by their deficiency of T cell antigens Leu-1 and/or Leu-9 in eight of nine cases. Neither Ki-1 nor Leu-M1 were reliable markers for lymphomatoid papulosis in this series, since large atypical cells were Ki-1-positive in only three of eight cases and were Leu-M1-negative in all eight cases tested. The remainder of the cutaneous infiltrate consisted of small T cells, macrophages, Langerhans cells, and granulocytes. The small T cells expressed a normal phenotype except in some cases associated with mycosis fungoides in which they were deficient in various T cell antigens. Comparison of concurrent lymphomatoid papulosis and mycosis fungoides skin biopsy specimens in two patients revealed that they were composed of phenotypically distinct T cell subpopulations. These results indicate that the large atypical cells of lymphomatoid papulosis are a proliferating population of activated helper T cells that are deficient in certain T cell antigens. Such abnormal T cell phenotypes are common in T cell lymphoma but are rarely, if ever, observed in cutaneous inflammation. In conjunction with the cytologic atypia, aneuploidy, and association with other lymphomas documented in this or previous reports, these data suggest that lymphomatoid papulosis represents a T cell lymphoproliferative disorder rather than an inflammatory disorder.