Fractalkine and macrophage-derived chemokine: T cell-attracting chemokines expressed in T cell area dendritic cells

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Abstract
Dendritic cells (DC) are a system of antigen‐presenting cells specialized in interaction with T cells. Recently it has been reported that DC can produce CC (β) chemokines that attract T cells. In this study we isolated mouse fractalkine and macrophage‐derived chemokine (MDC) belonging to CX3C (δ) and CC chemokine families, respectively, from bone marrow‐derived mature DC. While expression of fractalkine, which has so far been only examined in the brain and in vitro endothelial cells so far, was rather ubiquitous, MDC, which has been reported to be synthesized by macrophages and DC, was expressed specifically in the thymus and lymphnode. This is the first report that indicates fractalkine expression by DC. Expression of fractalkine and MDC mRNA increased with maturation of DC during in vitro culture of bone marrow cells. Spleen‐ and epidermis‐derived mature DC in culture also expressed these chemokines. Furthermore, their expression was detected selectively by Northern hybridization in CD11c+ B220– DC freshly purified from lymph nodes, and in large stellate cells in the lymph node T cell areas by in situ hybridization. Conditioned media of 293T cells transfected with these chemokine cDNA were chemotactic to Con A‐activated splenic T cells as well as the mouse T cell line EL4. In conclusion, while fractalkine and MDC belong to different families of chemokines, both may be involved in recruitment of T cells for interaction with mature DC in the immune response.