Objective: To clarify the involvement of dendritic cells (DCs), chemokines, and proinflammatory Th1 cytokines in the pathogenesis of the chronic muscle diseases dermatomyositis (DM) and polymyositis (PM).
Methods: We characterized by immunohistochemistry the DC subsets and their interaction with cells producing chemokines and the Th1 cytokines interleukin-17 (IL-17) and interferon-gamma (IFNgamma). Immature and mature DCs were defined by the expression of CD1a and DC-LAMP/CD83, respectively.
Results: Immature DCs were mainly detected in lymphocytic infiltrates in DM and PM muscle tissue samples. Mature DCs were detected in perivascular infiltrates and surrounded muscle fibers. IL-17-positive and IFNgamma-positive cells were also observed in perivascular infiltrates in both cases. We then focused on the expression of the CCL20/CCR6 chemokine/receptor complex, which controls immature DC migration, and on the expression of the CCL19/CCR7 and CCL21/CCR7 chemokine/receptor complexes, which control mature DC migration. CCL20 and CCR6 colocalized in lymphocytic infiltrates in DM and PM samples. CCL21 was rarely observed in DM samples and never observed in PM samples. CCL19- and CCR7-expressing cells were absent in both tissues.
Conclusion: The close association between CCL20/CCR6 and immature DCs suggests the contribution of CCL20 to CCR6+ immature DC homing. Detection of mature DCs in DM and PM muscle tissue samples despite the lack of CCL19 and CCR7 is evidence for a local maturation of DCs in inflammatory muscle tissue without lymphoid organ organization.