Cytomegalovirus infection is associated with absence of alveolar epithelial cell HLA class II antigen expression

Cytomegalovirus (CMV) pneumonia is associated with the development of secondary immunosuppression with resultant bacterial and fungal superinfections. Because class II HLA expression within the lung may be important in normal pulmonary cell-mediated immunity, the association of CMV infection of alveolar epithelial cells (AEC) with an absence of HLA class II antigens was tested. Using dual-labeling immunohistochemistry to detect CMV, AEC, endothelial cells, macrophages, and HLA class II antigens, lung tissue from patients whom died with CMV pneumonia was examined. Seventy-five percent of infected cells were AEC. In contrast to adjacent noninfected AEC, which expressed HLA-DR antigens, 91% of infected AEC were negative. There was no difference in this expression pattern between patients with or without AIDS. The absence of HLA class II antigens on infected AEC may account, in part, for the secondary immunosuppression associated with CMV pneumonia.