TNF alpha and IL-1beta mediate intercellular adhesion molecule-1 induction via microglia-astrocyte interaction in CNS radiation injury.

Radiation injury to the central nervous system (CNS) results in glial activation accompanied by expression of pro-inflammatory cytokines and adhesion molecules. In this study we demonstrate intercellular adhesion molecule-1 (ICAM-1) induction in the irradiated mouse brain at the mRNA and protein levels. Immunocytochemical analysis revealed that ICAM-1 protein was primarily expressed in endothelial cells and microglia. In vitro, ionizing radiation significantly induces TNF alpha, IL-1beta and ICAM-1 mRNA in primary microglia cultures. Interestingly, although ionizing radiation activated primary astrocyte cultures, it did not induce ICAM-1 expression. However, exposure of astrocytes to conditioned medium collected from irradiated microglia resulted in ICAM-1 induction, which was abrogated when the conditioned medium was pre-incubated with neutralizing antibodies raised against murine TNF alpha and IL-1beta. These results indicate that pro-inflammatory cytokines may be necessary for ICAM-1 expression in astrocytes in CNS radiation injury.