Histopathological analysis of H&E-stained lung sections showed that the lungs of control CD40L vector–immunized infected mice had signs of interstitial pneumonia with thickened alveolar septa and inflammatory cell infiltration; the lungs of mice immunized with the epitope-expressing vectors showed little sign of pneumonia with few infiltrating inflammatory cells (Supplemental Figure 3). This evidence concerns the gene CD40LG and pneumonia.