CD40 signaling in human dendritic cells is initiated within membrane rafts

Despite CD40's role in stimulating dendritic cells (DCs) for efficient spec ific T-cell stimulation, its signal transduction components in DCs are stil l poorly documented, We show that CD40 receptors on human monocyte-derived DCs associate with sphingolipid- and cholesterol-rich plasma membrane micro domains, termed membrane rafts. Following engagement, CD40 utilizes membran e raft-associated Lyn Src family kinase, and possibly other raft-associated Src family kinases, to initiate tyrosine phosphorylation of intracellular substrates, CD40 engagement also leads to a membrane raft-restricted recrui tment of tumor necrosis factor (TNF) receptor-associated factor (TRAF) 3 an d, to a lesser extent, TRAF2, to CD40's cytoplasmic tail. Thus, the membran e raft structure plays an integral role in proximal events of CD40 signalin g in DCs, We demonstrate that stimulation of Src family kinase within membr ane rafts initiates a pathway implicating ERK activation, which leads to in terleukin (IL)-1 alpha/beta and IL-1Ra mRNA production and contributes to p 38-dependent IL-12 mRNA production, These results provide the first evidenc e that membrane rafts play a critical role in initiation of CD40 signaling in DCs, and delineate the outcome of CD40-mediated pathways on cytokine pro duction.