Immunohistochemical detection of human milk components aspirated in lungs of an infant

Multidisciplinary approach to suspected sudden unexpected infant death caused by milk-aspiration: A case report

BACKGROUND

The term sudden unexpected infant death (SUID) is not always properly invoked. It refers to a broad range of conditions that sometimes defy classification. There is not only a strong emotional impact on the family, but such cases are also quite complex. Underlying causes may be multiple, not always readily apparent, and have potential repercussions, especially in terms of forensics.

CASE SUMMARY

A 5-month-old male baby was pronounced dead following acute lung failure and cardiopulmonary arrest. The parents had immediately rushed their child to the hospital, stating the baby was found prone and not breathing. Total-body postmortem computed tomography (PMCT) was performed, revealing a hypodense material of indeterminate nature within the main airways and areas of ground-glass parenchymal change. At autopsy, the respiratory tract mucosa appeared edematous and was coated with a whitish stringy material. There was widespread airspace reduction due to parenchymal collapse. Alveolar sacs and bronchial openings contained abundant amorphous material admixed with white blood cells. Immunohistochemical studies were performed, targeting CD15, CD68, and alpha-lactalbumin. Ultimately, the focus was on alpha-lactalbumin (milk protein), which showed marked immunopositivity within alveolar spaces. Cytoplasmic staining of macrophages was also particularly prominent.

CONCLUSION

Postmortem investigations are thus essential to identify causes of death and surrounding circumstances. PMCT is a useful tool in this setting, given the frequent dearth of autopsy findings and ambiguity as to cause of death in SUID cases. These findings, later confirmed by immunohistochemical investigations, were indicative of active pneumonia due to aspirated milk. The present account illustrates the importance a broad diagnostic approach to SUID in cases of forensic concern. PMCT is a very valuable aid in cases of forensic interest, as it can provide useful information in all those situations in which the cause of death is uncertain or there are no suggestive dynamics or lesions.

Longitudinal evaluation of immunohistochemical findings of milk aspiration: an experimental study using a murine model

To examine the longitudinal change of pathological findings of the lung and other organs in milk aspiration, an experimental study using a murine model was carried out. Either 0.5 or 1.0 ml cow's milk was instilled into the trachea of rats. From immediately after to 14 days after instillation, the animals were sacrificed, and the lungs, liver, kidneys, and spleen were removed. The results of immunostaining with anti-human α lactalbumin antibody indicated that not only the lung but also the kidney and spleen showed a positive reaction against the antibody over time. Experimentally aspirated milk was detectable in alveoli until 2 days after instillation. It was also detectable in renal tubules from 1 to 6h after instillation. Macrophages containing granules of aspirated milk were observed in splenic red pulp from 3h to 14 days after instillation. Detection of aspirated milk in other organs except the lung would be clear evidence of intravital milk aspiration and would suggest previous or recurrent milk aspiration.

Screening of milk aspiration in 105 infant death cases by immunostaining with anti-human alpha-lactalbumin antibody

To determine the frequency and degree of milk aspiration in infant death cases, immunohistochemical examinations were performed on lung sections from 41 sudden death cases and 64 in-hospital death cases using anti-human alpha-lactalbumin antibody. Milk aspiration to some degree was detected in more than half of the sudden death cases and in about one-third of the in-hospital death cases. A semi-quantitative examination of the amount of aspirated milk was subsequently performed in the positive cases. The amount of aspirated milk in the sudden death cases was significantly higher than that in the in-hospital death cases. The frequency distribution of the amount of aspirated milk was similar in shape in both groups. In most cases, a very small amount of aspirated milk was detected. The aspirated milk was assumed to be a result of occasional gastroesophageal reflux or cardiopulmonary resuscitation. However, in five cases, much larger amounts of aspirated milk were found. In these cases, milk aspiration may have been an important part of the cause of death. We concluded that slight milk aspiration is not rare in infant death cases, and that in a few cases, the aspiration is lethal. An immunohistochemical screening test is available to perform a postmortem diagnosis in these cases.

Immunohistochemical examination of the lungs in infant death cases using antibodies against milk components

To examine the use of immunohistochemical staining with antibodies against milk components for detection of aspirated milk on lung sections, eighteen infant death cases were investigated. Immunostaining was performed with anti-human alpha lactalbumin, anti-human IgA, anti-human milk fat globulin 1, and anti-cow whey antibody. Reactivity with each antibody was examined, and semi-quantitative examinations were performed to compare the amount of aspirated milk using anti-human alpha lactalbumin antibody. Materials in the alveoli or bronchioli on lung sections suspected to be aspirated milk showed the most sensitive and clearest reaction with anti-human alpha lactalbumin antibody. Of the eighteen cases, ten cases showed positive reaction with this antibody. The amount of aspirated milk varied widely in each case. In conclusion, immunohistochemical staining with antibodies against human milk components, especially anti-human alpha lactalbumin antibody, can detect small amounts of milk. Using this method, we were able to compare the relative amount of aspirated milk among cases.