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Abundance of type XVI collagen mRNA in normal human dermal fibroblasts explanted from different horizontal layers was determined using RNase protection assays. Type XVI collagen mRNA level in the fibroblasts explanted from the upper dermis was greater than those of the middle and lower dermis. The antibody raised against the synthetic N-terminal noncollagenous region reacted with approximately 210 kDa collagenous polypeptide in the culture medium of fibroblasts. Immunohistochemical study of normal human skin demonstrated that the antibody reacted preferentially with the fibroblasts and the extracellular matrix in the upper dermis rather than those in the middle and lower dermis. Type XVI collagen mRNA level was elevated 2.3-fold in localized scleroderma and 3.6-fold in systemic scleroderma compared with keloid and normal controls. Immunofluorescent study revealed that an intense immunoreactivity with the antibody was observed in the upper to lower dermal matrix and fibroblasts in the skin of systemic scleroderma as compared with normal skin. The results suggest that expression of type XVI collagen, a member of fibril-associated collagens with interrupted triple helices, in human skin fibroblasts can be heterogeneous in the dermal layers and can be modulated by some fibrotic diseases.

We have previously reported that connective tissue cells in the superficial dermis preferentially express alpha1(XVI) collagen rather than those in the lower dermis. Double immunofluorescence labeling using the antibodies for alpha1(XVI) collagen and factor XIIIa (plasma transglutaminase), which is a marker of dermal dendrocytes, demonstrated that both antibodies reacted with the same cells in the superficial dermis of normal skin as well as the lesional skins of dermal dendrocyte-related disorders, dermatofibroma, and psoriasis. Dermal dendrocytes are considered to be established by a culture of peripheral blood monocytes in the presence of granulocyte macrophage-colony stimulating factor and interleukin-4. Reverse transcription--polymerase chain reaction, metabolic labeling, and immunofluorescence studies demonstrated that treatment of CD14+ peripheral blood monocytes with granulocyte macrophage-colony stimulating factor/interleukin-4 over a period of 8 d resulted in the induction of alpha1(XVI) collagen as well as factor XIIIa. The physiologic significance of colocalization of alpha1(XVI) collagen and factor XIIIa in the tissue and their coordinate induction in CD14+ monocyte-derived dendritic cells in vitro was studied. Considerable incorporation of [3H]putrescine by factor XIIIa into recombinant noncollagenous domain (NC) 11 but not into collagenous domain (COL) 1.NC1 domain of the alpha1(XVI) polypeptide was found. Incubation of recombinant NC11 of alpha1(XVI) polypeptide with factor XIIIa in vitro produced a covalent cross-linking complex on sodium dodecylsulfate-polyacrylamide gel electrophoresis. The results indicate that alpha1(XVI) collagen is constitutively expressed by most dermal dendrocytes in the skin and dendritic cells differentiated from peripheral blood monocytes in vitro. Type XVI collagen is expressed in factor XIIIa+ dermal dendrocytes and may form an intermolecular cross-linking through NC11 domain by the reaction catalyzed by factor XIIIa contributing to the structural integrity of factor XIIIa+ dendritic cell-rich tissues.

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