Purpose of review: Asthma is a heterogeneous disease with unknown cause; however, allergic asthma is driven largely by Th2-type immune responses. The pathways that interact to induce Th1 and Th17-type immune responses are well understood; however, until recently the innate immune pathways involved in the induction of Th2-type immunity were unknown. In this review we sought to outline many of the recent advances in uncovering the cell and molecular mechanisms that generate Th2 responses.
Recent findings: It is clear that the Th2 pathway can no longer be considered a ‘default pathway’ of the lung immune system as multiple cells and cytokines have now been identified that work to actively instruct Th2 differentiation. Basophils and dendritic cells have been investigated for their critical role in Th2 induction, and newly identified cell subsets have also been shown to play an important function in Th2 responses. The identification of the Th2-inducing cytokines IL-25, IL-33 and thymic stromal lymphopoietin has also accelerated studies examining the development of Th2 responses in asthma.
Summary: Studies of the role played by the innate immune system in the induction of Th2 responses have begun to unravel the cellular and molecular mechanisms potentially underlying the pathogenesis of allergic asthma. Further study in this area may lead to the discovery of new therapeutics for the treatment of allergic disease.