Allergen recognition by specific effector Th2 cells enables IL-2-dependent activation of regulatory T-cell responses in humans

Type 2 allergen-specific T cells are essential for the induction and maintenance of allergies to foods, and Tregs specific for these allergens are assumed to be involved in their resolution. However, it has not been convincingly demonstrated whether allergen-specific Treg responses are responsible for the generation of oral tolerance in humans. We observed that sustained food allergen exposure in the form of oral immunotherapy resulted in increased frequency of Tregs only in individuals with lasting clinical tolerance. We sought to identify regulatory components of the CD4+ T-cell response to food allergens by studying their functional activation over time in vitro and in vivo. Two subsets of Tregs expressing CD137 or CD25/OX40 were identified with a delayed kinetics of activation compared with clonally enriched pathogenic effector Th2 cells. Treg activation was dependent on IL-2 derived from effector T cells. In vivo exposure to peanut in the form of an oral food challenge of allergic subjects induced a delayed and persistent activation of Tregs after initiation of the allergen-specific Th2 response. The novel finding of our work is that a sustained wave of Treg activation is induced by the release of IL-2 from Th2 effector cells, with the implication that therapeutic administration of IL-2 could improve current OIT approaches.

Variability of blood eosinophils in patients in a clinic for severe asthma

BACKGROUND

Blood eosinophils are used to determine eligibility for agents targeting IL-5 in patients with uncontrolled asthma. However, little is known about the variability of blood eosinophil measures in these patients before treatment initiation.

OBJECTIVE

To characterize variability and patterns of variability of blood eosinophil levels in a real-world clinic for severe asthmatics.

METHODS

Retrospective review of blood eosinophils measured over a 5-year period in patients enrolled in an urban clinic. Repeated measures of blood eosinophil levels in individuals were evaluated, and cluster analysis was performed to characterize patients by eosinophil patterns. Clinical characteristics associated with eosinophil levels and patterns of variability were analysed.

RESULTS

Patients treated in the Bellevue Hospital Asthma Clinic within a 3-month period were identified (n = 219). Blood eosinophil measures were obtained over the previous 5 years. Only 6% (n = 13) of patients had levels that were consistently above 300 cells/μL. Nearly 50% (n = 104) had eosinophil levels that traversed the threshold of 300 cells/μL. In contrast, 102 (46%) had levels that never reached the threshold of 300 cells/μL. Cluster analyses revealed three clusters with differing patterns of levels and variability. There was a suggestion of decreased clinical control and increased atopy in the cluster with the greatest variability in blood eosinophil measures.

CONCLUSION

In an urban clinic for patients referred for uncontrolled asthma, blood measures of eosinophils were variable and showed differing patterns of variability. These data reinforce the need to perform repeated eosinophil blood measures for appropriate designation for therapeutic intervention.

Regulation of CD8 T cell responses by follicular dendritic cell-bound antigen (98.17)

Follicular dendritic cells (FDCs) are well known to retain the immune complexes that drive antibody affinity maturation. Here, we present evidence that FDC-bound antigens are also persistently sampled by bone marrow-derived DCs for presentation to CD8 T cells. These results are based upon our previous observation that ovalbumin (OVA) expressed in transmembrane form by the placenta is hematogenously released during pregnancy to accumulate on maternal FDCs throughout all secondary lymphoid organs. We now show that OVA loading onto FDCs is complement-dependent and that bound OVA is retained for several weeks after delivery. Strikingly, antigen retention correlated with a prolonged postpartum phase of OVA presentation to CD8 T cells that could be abrogated by the pharmacological ablation of FDC networks. Furthermore, bone marrow chimera experiments demonstrated that FDC-bound OVA could be acquired de novo by DCs arising in the postpartum period. The presentation of placental OVA acquired from FDC-associated depots was highly tolerogenic as it induced T cell deletion even in the presence of exogenous adjuvants. These results suggest an unanticipated level of control over peripheral tolerance induction potentially relevant to the pathogenesis of systemic lupus erythematosus, an autoimmune disease characterized by impaired tolerance to apoptosis-associated antigens opsonized by the complement system. Supported by NIH grant RO1-AI062980.