An Introduction to Cutaneous DCs

DCs, a growing family of morphologically and functionally defined cells, can be found in small percentages in most organs of the human body and may be further divided into a myeloid and a lymphoid type (Banchereau et al. 1998, Steinman 1991). DCs are considered to be the most potent antigen-presenting cells (APCs) of the human body and are capable of initiating both primary and secondary immune responses. The term "dendritic cells" was coined in 1973, when Steinmann et al. (Steinman et al. 1973) described a novel cell population in murine spleen cell suspensions. As a rule, T cells require efficient stimulation by APCs to become effector cells and to become involved in pathophysiologic processes. DCs originate from bone marrow precursors and are found in small amounts in most organs of the human body. Studies have shown that DCs can differentiate in vitro from human blood monocytes (Sallusto and Lanzavecchia 1994).

Two major DC types are found in normal human skin: epidermal Langerhans' cells (LCs) and dermal DCs (DDCs). In contrast, inflammatory skin may harbor considerable numbers of two additional major types of DCs: inflammatory dendritic epidermal cells (IDECs) and plasmocytoid DCs (PDCs) (Wollenberg et al. 1996,2002)(Fig. 20.1). Although LCs, IDECs, and PDCs are well-defined entities, the pool of DDCs probably comprises a heterogenous mixture of different cell types. In addition, any u

U 102

IDEC

: LC

PDC

Normal human skin u

U 102

IDEC

Atopic dermatitis

101 102 10* CD123 PE

Psoriasis vulgaris

Contact dermatitis tH

101 10á CD123 PE

Lupus erythematosus

101 10á CD123 PE

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200 400 600 800 1000

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Fig. 20.1a, b. PDCs, LCs, and IDECs in normal skin and in lesional skin from patients with atopic dermatitis, psoriasis vulgaris, contact dermatitis, and lupus erythematosus. Epidermal single cell suspensions were prepared from biopsies of normal skin and of lesional skin from patients with atopic dermatitis, psoriasis vulgaris, contact dermatitis, and lupus erythematosus, a Subsets of DCs (PDCs, IDECs, and LCs) were quantified by four-color-staining with HLA-DR (PerCP), lineage markers (FITC), CDllc (APC), and CD123 (PE). b The identity of PDCs is confirmed by the FSC and SSC characteristics known from peripheral blood derived PDCs (modified from Wollenberg et al. 2002).

APCs, antigen presenting cells; DCs, dendritic cells; FITC, fluoresceinisothiocyanate; FSC, forward light scatter; IDECs, inflammatory dendritic epidermal cells; LCs, Langerhans' cells; PDCs, plasmocytoid dendritic cells; PE, phycoerythrine; SSC, side light scatter

0 200 400 600 800 1000

0 200 400 600 800 1000

0 200 400 600 800 1000

200 400 600 800 1000

200 400 600 800 1000

Fig. 20.1a, b. PDCs, LCs, and IDECs in normal skin and in lesional skin from patients with atopic dermatitis, psoriasis vulgaris, contact dermatitis, and lupus erythematosus. Epidermal single cell suspensions were prepared from biopsies of normal skin and of lesional skin from patients with atopic dermatitis, psoriasis vulgaris, contact dermatitis, and lupus erythematosus, a Subsets of DCs (PDCs, IDECs, and LCs) were quantified by four-color-staining with HLA-DR (PerCP), lineage markers (FITC), CDllc (APC), and CD123 (PE). b The identity of PDCs is confirmed by the FSC and SSC characteristics known from peripheral blood derived PDCs (modified from Wollenberg et al. 2002).

APCs, antigen presenting cells; DCs, dendritic cells; FITC, fluoresceinisothiocyanate; FSC, forward light scatter; IDECs, inflammatory dendritic epidermal cells; LCs, Langerhans' cells; PDCs, plasmocytoid dendritic cells; PE, phycoerythrine; SSC, side light scatter epidermal nonkeratinocyte without cytoplasmic features such as melanosomes, Bir-beck granules, or Merkel cell granules may be labeled as "indeterminate cells" (Breathnach 1975). In normal skin, indeterminate cells are rare.

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