Immunologic functions of Langerhans cells

Controversies in mycosis fungoides

Most clinicians agree that mycosis fungoides is the prototypic cutaneous T cell lymphoma. However, certain clinical characteristics indicate that this disorder may begin as a reactive rather than a neoplastic process. The concept of a nonneoplastic etiopathogenesis of mycosis fungoides is further supported by recent data on the function of Langerhans cells, a population of epidermal cells known to play a critical role in immune surveillance and the development of contact sensitivity. It has been suggested that chronic occupational exposure to environmental allergens results in persistent antigenic stimulation, leading to a breakdown in immune surveillance and eventually, malignancy. Modern laboratory technics have enhanced the clinician's ability to diagnose and stage mycosis fungoides. Data obtained from such studies have indicated that systemic spread may occur much earlier in the course of disease than has previously been appreciated. The therapeutic implications of such knowledge are as yet uncertain.

Separation of human skin cells by velocity sedimentation into functionally distinct fractions

The epidermis consists of a heterogeneous population of cells including Langerhans cells, Merkel cells, melanocytes, and keratinocytes in various stages of differentiation. The current study was undertaken to determine if skin cell suspensions can be separated into morphologically and/or functionally distinct fractions. Skin cells were suspended by trypsinization and separated into multiple fractions by velocity sedimentation. Certain fractions reproducibly stimulated proliferation of allogeneic lymphocytes in the skin cell lymphocyte reaction, whereas other fractions, containing larger cells, supported growth of keratinocyte colonies in cell cultures. These results indicate that stimulation in the skin cell lymphocyte reaction and growth of keratinocyte colonies are mediated by distinct cells, separable by velocity sedimentation.

The Langerhans cell: the master key to contact dermatitis: a hypothesis

A tentative model is presented which is based on existing published data. The model suggests that the epidermal Langerhans cell plays a central role in contact dermatitis by proliferation control of keratinocytes and as the most peripheral outpost of the immune system. Contact dermatitis to chemicals is the injurious expression of a defense mechanism designed phylogenetically against arthropods and insects.