Macrophage-derived chemokine (MDC/CCL22) and CCR4 are involved in the formation of T lymphocyte-dendritic cell clusters in human inflamed skin and secondary lymphoid tissue

Our previous study demonstrated formation of T cell-dendritic cell (DC) clu sters in inflamed dermis of intraorally autotransplanted skin flaps. Such T cell-DC clusters are supposed to be important for close interactions betwe en T cells and DCs including the specific antigen presentation. Here we sho w the involvement of the macrophage-derived chemokine (MDC/CCL22) and its s pecific receptor CC chemokine receptor 4 (CCR4) in the formation of T cell- DC clusters. Reverse transcriptase-polymerase chain reaction analysis revea led high levels of mRNA expression for MDC and CCR4 in inflamed skin and ne ck lymph nodes (LNs), but not In normal skin. Immunohistochemically, MDC+ c ells and CCR4(+) cells were mainly located within the T cell-DC clusters bo th in the dermis of inflamed skin and the T cell area of LNs. MDC+ cells we re identified to be DCs both in inflamed skin and LNs. The majority of CCR4 + cells were CD4(+) T cells, accounting for approximately one-third of tota l CD4(+) T cells in the inflamed skin. Our data suggest that the MDC-CCR4 s ystem plays an important role in the formation of T cell-DC clusters both i n inflamed skin and LNs.