Background: The role of lower respiratory tract illnesses (LRIs) in the development of allergies is not well understood. The relation of wheezing and non-wheezing LRIs to serum IgE levels and atopy was studied in 888 children.

Methods: Total serum IgE levels were measured at birth, nine months and six years of age; and interferon gamma production by blood mononuclear cells was measured at birth and nine months. Atopy was determined by skin prick tests at age six. Wheezing and non-wheezing LRIs up to age three were diagnosed by a physician.

Results: Cord serum IgE levels were similar between all LRI groups and the no LRI group. Children who had wheezing LRIs until the age of three had IgE levels at nine months and at six years within normal ranges for age. In contrast, children who had a non-wheezing LRI before the nine month IgE sample had lower IgE levels at nine months and six years (geometric mean 1.8 IU/ml and 9.9 IU/ml, respectively) compared with children who had no LRIs (3.9 IU/ml and 38.3 IU/ml, respectively). Children who had non-wheezing LRIs after the nine month IgE sample had normal nine month IgE levels (3.2 IU/ml) but decreased IgE levels at six years of age (15.7 IU/ml). Children with more than one non-wheezing LRI before the age of three were less likely to be atopic than those with no LRI (odds radio 0.2). Interferon gamma production was higher in the non-wheezing LRI group at nine months than in the no LRI or wheezing LRI groups.

Conclusions: Non-wheezing LRIs are associated with subsequent depression of IgE levels and reduced skin test reactivity.