Our prospective, longitudinal study on the natural course of CMA showed that IgE and IgG4 antibodies recognize similar epitopes on the various CM proteins. The finding supports the hypothesis that IgG4 induces tolerance by blocking the binding of specific IgE to allergen (14
). We observed that an increase in the intensity of IgG4 binding to CM epitopes occurred concurrently with a decrease in IgE binding intensity among patients who recovered early from CMA. This is consistent with previous observations on levels of antigen specific IgE and IgG4 in the natural course of hen's egg allergy (19
), in desensitization to CM (16
) or peanut (17
) and in successful aeroallergen specific immunotherapy (13
Epitope recognition patterns of IgE and IgA had little overlap. It may reflect the observation that specific IgA, in contrast to IgG4, does not inhibit IgE binding (18
). The intensity of peptide binding by IgA increased over time in children with persisting CMA, whereas it changed little in children with early recovery. Furthermore, the estimated differences between IgE binding intensity and that of IgA showed no group-associated trend. Our data thus do not fully support the reported role of serum IgA in tolerance development (15
). A possible technical reason for the low IgA binding signal in α-caseins is that the more sensitive dendrimer amplification was not applied to the IgA assay.
The IgE epitope recognition profile in patients with persisting CMA at the age of 8-9 years was stable over time, whereas patients who recovered by the age of 3 years lost peptide-specific binding activity over time. The observation is consistent with reports that broader epitope profiles are associated with persisting CMA (10
). The greater intensity of IgE binding signal in patients with persisting CMA is in accordance with results that higher CM specific IgE levels predict prolonged clinical reactivity to CM (6
IgE binding patterns were similar at the time of diagnosis in both patient groups and thus did not provide prognostic information. However, children with persisting CMA recognized peptide regions in β-casein, β-lactoglobulin and κ-casein with greater intensity than children with early recovery. IgE binding of regions in these proteins have been associated with persisting CMA (11
). Previous studies indicated that IgE binding to α-casein epitopes may predict the natural course of CMA (10
). In our prospective study, α-casein epitopes had no predictive value at the time of diagnosis, but a year later and especially at the time of follow-up, when children in the group of early recovery already tolerated CM, binding intensity was greater in children with persisting CMA. However, the random decision tree analysis revealed that combining IgE and IgG4 binding data at the time of diagnosis on relatively few regions in αs1-, αs2-, β- and κ-casein predicted with significant accuracy whether a child would recover from CMA early or have persisting allergy.
The discrepancies between this and previous studies on IgE epitope recognition may arise from differences in subject selection and characteristics, from the variability of IgE epitope profiles (9
), and from divergence in the stages of CMA under investigation. In this prospective study, CMA was diagnosed at a mean age of 7 months, which was on average within four months from the first symptoms (2
). The relatively low CM-specific IgE levels therefore reflect the relatively short period of CM sensitization. Furthermore, we investigated samples from the early (at diagnosis and one year after) and later (at mean age 8.6 years) stages of CMA. Subjects in earlier studies (10
) had considerably higher CM specific IgE levels and more severe symptoms, including anaphylaxis, than children in the current study, and samples were drawn at school age. Cerecedo et al (11
) investigated patients with CM-specific IgE levels more comparable to those in the current study, but they compared CMA patients who were reactive or tolerant to CM at a much younger age (median age 2 years, range 2-4 months). Since patients with CMA have the potential of recovery at any age (6
), the life-time prognosis of patients with persisting CMA at school age (10
) (and in the current study) or at toddler age (11
) may differ. Differences in methods, allergen sensitivity, and type of statistical analysis may also contribute to the variation between studies.
Our study demonstrates the significance of decreasing IgE recognition of allergen epitopes with a concurrent increase in corresponding IgG4 recognition in the development of allergen tolerance, whereas the role of circulating specific IgA remains unclear. These findings can potentially be utilized to predict prognosis and to develop novel immunotherapeutic modalities for the treatment of food allergies.
Cow's milk epitope binding by IgE is stable over time in children with persisting cow's milk allergy, whereas it decreases in those who recover early. Binding patterns by IgE overlap with IgG4, but not IgA.