A recent immunohistochemical study found increased numbers of eosinophils, but no mast cells, in the pulmonary parenchyma of infants who died of
sudden infant death syndrome (
SIDS). The present study tested the hypothesis that this
pulmonary eosinophilia could be
IgE-mediated. Histomorphometry was used to compare the numbers of eosinophils, mast cells, and
IgG-,
IgA-,
IgM- and
IgE-expressing lymphoid cells in the lungs of two groups of infants. Twenty-eight subjects aged less than 1 year were selected from post-mortem records of
infant deaths between 1989 and 1992. Fourteen were cases of
SIDS and these infants were matched for age and gender to 14 controls who died of other non-pulmonary conditions. Immunohistochemical stains were used and positive cells were counted on six peribronchial and six subpleural fields. The numbers of eosinophils in both peribronchial and subpleural regions were significantly higher in
SIDS compared with controls (P = 0.0071 and P = 0.041, respectively). The numbers of
IgA-expressing lymphoid cells were also significantly increased in
SIDS cases (P = 0.042). There were no differences in
IgG,
IgM or
IgE expression or in mast cell numbers. These results confirmed that pulmonary eosinophils are increased in
SIDS, but not through an
IgE-mediated pathway.