Immunophenotypical Characterization of Macrophages in Rat Bleomycin-Induced Scleroderma

Scleroderma is a skin disorder characterized by persistent fibrosis. Macrophage properties influencing cutaneous fibrogenesis remain to be fully elucidated. In this rat (F344 rats) model of scleroderma, at 1, 2, 3, and 4 weeks after initiation of daily subcutaneous injections of bleomycin (BLM; 100 μl of 1 mg/ml daily), skin samples were collected for histological and immunohistochemical evaluations. Immunohistochemically, the numbers of cells reacting to ED1 (anti-CD68; phagocytic activity) and ED2 (anti-CD163; inflammatory factor production) began to increase at week 1, peaked at week 2, and decreased thereafter. In contrast, the increased number of cells reacting to OX6 (anti–MHC class II molecules) was seen from week 2 and remained elevated until week 4. α–Smooth muscle actin–positive myofibroblasts were increased for 4 weeks. Double labeling revealed that galectin-3, a regulator of fibrogenic factor TGF-β1, was expressed in CD68+, CD163+, and MHC class II+ macrophages and myofibroblasts. mRNA expression of TGF-β1, as well as MCP-1 and CSF-1 (both macrophage function modulators), were significantly elevated at weeks 1 to 4. This study shows that the increased number of macrophages with heterogeneous immunophenotypes, which might be induced by MCP-1 and CSF-1, could participate in the sclerotic lesion formation, presumably through increased fibrogenic factors such as galectin-3 and TGF-β1; the data may provide useful information to understand the pathogenesis of the human scleroderma condition.