Furthermore, computed tomography (CT) morphology revealed that high density increased throughout the lungs (typical signs of acute pneumonia) after MHV-A59 infection in CD4–TREM-2 KO versus WT mice after 5 days intranasally (Fig. 6E), and hematoxylin and eosin staining showed that the deficiency of TREM-2 in CD4+ T cells accelerated the lung destruction (Fig. 6F). This evidence concerns the gene CD4 and pneumonia.