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.