The role of CD44 during CD40 ligand-induced dendritic cell clustering and maturation

The interaction between CD40 on dendritic cells (DC) and its ligand CD154 has been recognized to be an important feature in the maturation of DC. Here, we were interested in the role of CD44 a surface receptor shown to mediate cell-cell adhesion and binding to Hyaluronic acid (HA). Western blot analysis of human DC stimulated for 3-12 h with CD154 revealed the rapid induction of the 85 kDa standard form of CD44 and an increased HA-binding affinity. Time-lapse video-imaging microscopy of human DC co-cultured on CD154-transfected murine fibroblasts showed that the CD44 up-regulation coincided with the rapid induction of homotypic DC clustering, which did not occur on empty vector-transfected fibroblasts. In this system, addition of anti-CD44s mAbs abrogated DC-cluster formation, thereby inhibiting further maturation, as shown by a reduced TNF-alpha production and inhibition of CD154-induced MHC class II up-regulation. However, co-incubation with HA-degrading enzymes induced no changes in the CD154-mediated DC clustering and maturation.