Immunological Aspects of the Atopic March

In addition to the original description of the atopic march as a fixed sequence of clinical features, data from birth cohorts suggest an immunological counterpart. The development of atopic sensitization has been found to loosely follow a pattern starting with immunoglobulin E (IgE) to foods (milk and, unexpectedly, egg), then indoor airborne allergens (particularly mites), and finally, outdoor allergens (typically from pollen). For the different allergen source materials, the aim is to identify allergens that are prone to initiate sensitization. For house dust mites, no convincing initiator has been identified. For grass pollen, group 1 allergen was the probable initiator in 75% of children. A plausible scenario for the subsequent expansion of repertoire is that mucosal inflammation induced by allergen–IgE–mast cell reactions creates a milieu that facilitates new sensitizations. Although the recent cohort data do not yet add convincing support for this hypothesis, it remains an important topic for further investigation.