Analysis of the oligomeric requirement for signaling by CD40 using solublemultimeric forms of its ligand, CD154

We describe the construction of a novel soluble dodecameric form of CD154 ( CD40 ligand) that is more effective than trimeric tCD154 in triggering B ce ll activation. Dodecameric surfactant protein (SP)-D-CD154 was more potent than tCD154 in inducing B cell proliferation over a wide range of concentra tions. At saturating concentrations, the level of proliferation triggered b y SP-D-CD154 was fourfold higher than that achieved with tCD154. Moreover, stimulation with dodecameric CD154 induced higher levels of the costimulato ry molecules ICAM-1 and CD86. The higher activity of dodecameric CD154 when compared to trimeric CD154 is unlikely to be due to differences in their a vidity for CD40, since both forms bound to CD40 strongly. Therefore, the ex tent of receptor clustering directly regulates signaling by CD40.