Blockade of CD40–CD40 Ligand Interactions Protects against Radiation-Induced Pulmonary Inflammation and Fibrosis

This study investigated whether CD40-CD40 ligand (L) interactions are important in mediating ionizing radiation-induced lung toxicity. Radiotherapy is a key component in the management of malignant diseases and is a conditioning regimen for bone marrow transplantation. Unfortunately, radiation therapy is particularly toxic to the lung, potentially inducing a fatal pneumonitis and fibrosis, thus limiting its effectiveness. There are no therapies that protect against the development of radiation-induced lung toxicity. Using a mouse model of radiation-induced lung toxicity, a monoclonal anti-CD40L antibody (MR1) that disrupts CD40-CD40L interactions was tested for the ability to reduce lung injury. C57BL/6 mice were pretreated with either nothing, MR1, or hamster IgG 24 h prior to a single dose of 15 Gray ionizing radiation to the thorax. During the following 26 weeks, mice continued to receive MR1 or hamster IgG twice per week. MR1 protected against death from radiation pneumonitis and fibrosis and dramatically reduced lung pathology as evidenced by a limited influx of inflammatory cells, minimal collagen deposition, and septal thickening. MR1 also prevented radiation-induced pulmonary mastocytosis and blunted expression of cyclooxygenase-2, a proinflammatory enzyme responsible for prostaglandin synthesis. Disruption of CD40-CD40L interactions may offer a new mode of intervention to protect against radiation-induced pulmonary toxicity.