Primary cutaneous lymphomas are a heterogeneous group of T- and B-cell lymphomas that present in the skin with no evidence of extracutaneous disease at the time of diagnosis. The 2005 World Health Organization–European Organization for Research and Treatment of Cancer (WHO-EORTC) consensus classification has served as a golden standard for the diagnosis and classification of these conditions. In September 2018, an updated version of the WHO-EORTC was published in the fourth edition of the WHO Classification of Skin Tumours Blue Book. In this classification, primary cutaneous acral CD8+ T-cell lymphoma and Epstein-Barr virus positive (EBV+) mucocutaneous ulcer are included as new provisional entities, and a new section on cutaneous forms of chronic active EBV disease has been added. The term “primary cutaneous CD4+ small/medium T-cell lymphoma” was modified to “primary cutaneous CD4+ small/medium T-cell lymphoproliferative disorder” because of its indolent clinical behavior and uncertain malignant potential. Modifications have also been made in the sections on lymphomatoid papulosis, increasing the spectrum of histologic and genetic types, and primary cutaneous marginal zone lymphomas recognizing 2 different subtypes. Herein, the characteristic features of these new and modified entities as well as the results of recent molecular studies with diagnostic, prognostic, and/or therapeutic significance for the different types of primary cutaneous lymphomas are reviewed. An update of the frequency and survival of the different types of primary cutaneous lymphomas is provided.

Natural killer (NK) cells are innate lymphocytes that provide cytokines critical for early host defense against pathogens. One subset of human NK cells (CD56bright) constitutively expresses the high-affinity interleukin 2 (IL-2) receptor and produces immunoregulatory cytokines. Here, we demonstrate that CD56bright NK cells are present in human lymph nodes and that endogenous T cell–derived IL-2, acting through the NK high-affinity IL-2 receptor, costimulates CD56bright NK cells to secrete IFN-γ. Thus, adaptive immunoregulators influence innate cytokine production, which in turn may influence the developing antigen-specific immune response. These data show a dynamic interaction between innate and adaptive human lymphocytes and emphasize the importance of studying interactions between immune components to understand the immune response as a whole.

Plasmacytoid dendritic cells are present in lymphoid and nonlymphoid tissue and contribute substantially to both innate and adaptive immunity. Recently, we have described several monoclonal antibodies that recognize a plasmacytoid dendritic cell-specific antigen, which we have termed BDCA-2. Molecular cloning of BDCA-2 revealed that BDCA-2 is a novel type II C-type lectin, which shows 50.7% sequence identity at the amino acid level to its putative murine ortholog, the murine dendritic cell–associated C-type lectin 2. Anti–BDCA-2 monoclonal antibodies are rapidly internalized and efficiently presented to T cells, indicating that BDCA-2 could play a role in ligand internalization and presentation. Furthermore, ligation of BDCA-2 potently suppresses induction of interferon α/β production in plasmacytoid dendritic cells, presumably by a mechanism dependent on calcium mobilization and protein-tyrosine phosphorylation by src-family protein-tyrosine kinases. Inasmuch as production of interferon α/β by plasmacytoid dendritic cells is considered to be a major pathophysiological factor in systemic lupus erythematosus, triggering of BDCA-2 should be evaluated as therapeutic strategy for blocking production of interferon α/β in systemic lupus erythematosus patients.