Phenotype, Ultrastructure, and Function of CD1+DR+ Epidermal Cells that Express CD36 (OKM5) in Cutaneous T‐Cell Lymphoma

This study investigated the phenotype and function of different antigen‐presenting cells (APC) present within the epidermis of patients with cutaneous T‐cell lymphoma (CTCL). Involved epidermis of CTCL compared with uninvolved was found to contain increased numbers of CDI + DR+ APC. This population was heterogeneous and comprised both leucocytes of a novel CD1+DR+CD36 (OK.M5)+ phenotype and CD1+DR+CD36− indeterminate/Langerhans cells. The CD1+DR+CD36+ leucocytes did not express TcR‐1, CD5, CD 15. or CD22, and only a minor population expressed CD11, demonslrating that they were neither T nor B cells, and did not belong lo the major CD11+ (OKM1+) blood monocyte population. Electron microscopy of purified CD36+ lesional epidermal cells (EC) demonstrated that they lacked Birbeck granules found on CD1+‐selected Langerhans cells, and most cells exhibited features of indeterminate cells or macrophages. The capacity of EC from involved epidermis to present alloanttgens was found to be increased relative to uninvolved epidermis in all patients tested, and this capacity was critically dependent upon the presence of CD45+ DR+ bone marrow‐derived cells but not on the presence of CD45+ DR+ keratinocytes. Positive selection using MoAb against CDI and CD36 demonstrated that both cell populations exhibited the capacity to stimulate T cells. The results indicate that a novel antigen‐presenting cell population with a unique phenotype is present within involved skin of patients with mycosis fungoides. These cells express CD36 in addition to CD1 and have an ultrastructural appearance consistent with a dendritic antigen‐presenting cell derivation.