Both Langerhans cells (LC) and dermal dendritic macrophages (DMΦ) deserve attention as antigen presenting cells in the skin, as reviewed elsewhere.1 The morphologic, antigenic and functional features of the formers are extensively dealt with in many chapters of this volume. Dendritic MΦ are characterized by the expression of CD36 antigen and contain many lysosomes;2 they can stimulate mixed cell reactions in vitro, but it is not known whether they stimulate immune responses in vivo or rather inhibit them, perhaps by activating suppressor cell circuits.3,4 The differentiation pathways of LC and DMΦ are incompletely known. The formers, in particular, are considered to derive from circulating precursors which express CD14 antigen “dimly”5 or not at all;6 it is not clear whether these precursors should be considered as true monocytes or a specialized cell type.7,8 It has been proposed that LC can differentiate from DMΦ, but the evidence in favour is weak.9
