An immunohistochemical study of pulmonary surfactant apoprotein A (SP-A) in forensic autopsy materials

SP-A is the most prevalent protein component of pulmonary surfactant which is essential to maintain alveolar stability. SP-A can be detected by immunohistochemistry and in such form it has been previously reported as a useful tool to distinguish aspyxial deaths from other hypoxic cases. The present immunohistochemical study shows the SP-A staining distribution among a selected forensic material to evaluate the effect of fluid accumulation in the lung interstitium and alveoli commonly related to pulmonary edema. A total of 48 cases were examined histologically and immuno-histochemically based on the presence/absence of pulmonary edema and survival time: 10 cases of acute cardiac deaths (ACDs) in which death occurred rapidly, in a few minutes from the beginning of the symptoms and without signs of pulmonary edema, 18 cases of drowning (12 in saltwater and 6 cases in freshwater), 20 cases of narcotic deaths (6 by cocaine and 14 by opiates) with gross pulmonary edema. The results suggest that edema fluid can produce some kind of molecular alterations of SP-A affecting immunostaining expression. The results show also that SP-A immunostaining patterns alone do not meet the requirements for general diagnostic use and cannot differentiate among fatalities. The SP-A expression needs to be preferably associated with the presence and intensity of histological signs according to suspected cause of death as well as type and amount of edema fluid commonly related to cardiac and/or respiratory failure (cardiogenic and non-cardiogenic pulmonary edema).