Ligation of microglial CD40 results in p44/42 mitogen-activated protein kinase-dependent TNF-alpha production that is opposed by TGF-beta 1 and IL-10

Recently, it has been demonstrated that the CD40 receptor is constitutively expressed on cultured microglia at low levels. Ligation of CD40 by CD40 li gand on these cells results in microglial activation, as measured by TNF-al pha production and neuronal injury. However, the intracellular events media ting this effect have get to be investigated. WE report that ligation of mi croglial CD40 triggers activation of p44/42 mitogen-activated protein kinas e (MAPK). This effect is evident 30 min posttreatment, and progressively de clines thereafter (from 30 to 240 min). Phosphorylated p38 MAPK is not obse rved in response to ligation of microglial CD40 across the time course exam ined. Inhibition of the upstream activator of p44/42 MAPK, mitogen-activate d protein/extra-cellular signal-related kinase kinase 1/2, with PD98059, de creases phosphorylation of p44/42 MAPK and significantly reduces TNF-alpha release following ligation of microglial CD40. Furthermore, cotreatment of microglial cells with CB40 ligand and TGF-beta 1 or IL-10, or both, inhibit s CD40-mediated activation of p44/42 MAPK and production of TNF-alpha in a statistically interactive manner. Taken together, these data show that liga tion of microglial CD40 triggers TNF-alpha release through the p44/42 MAPK pathway, an effect that can he opposed by TGF-beta 1 and IL-10.