Study on the Pathogenesis of the Cause of Death of Severe Acute Respiratory Syndrome--Acute Lung Injury and Secondary Infection

Objective To investigate the pathogenesis of the cause of death of severe acute respiratory syndrome (SARS). Method Tissue specimens from 4 cases of SARS were studied by HE staining and immunohistochemical technique. Results Lung tissue samples from two cases died at early phase revealed a mixed features of type Ⅱ alveolus cell and fibroblast hyperplasia, thicken walls of alveoli, engorgement and edematous of blood vessels, intra-alveolar exudation of fibrinoid materials, erythrocytes with hyaline-membrane formation, and pulmonary interstitial infiltration of mononuclear cells. The pathological changes of the lung tissues from another two dead cases with long courses of illness showed large amount of intra-alveolar aspergillus, and pulmonary vascular walls destruction with an invasion of aspergillus into blood vessels. The result of immunohistochemical study showed that CD45RO+ positive cells were found in those lung tissues but not CD20+ positive cells. There was increased number of CD68+ positive cells. Conclusions The results indicated that the pathological changes of lungs in SARS patients were acute lung injury. Hyper reaction of the immune system may be one of the reasons responsible for main cause of death at early phase after onset,but secondary fungi infection was an important cause of death in those SARS patients with significant immunodepression at late phase.