A novel functional mast cell assay for the detection of allergies.

BACKGROUND: Clinical management of allergic diseases has been hampered by the lack of safe and convenient tests to reliably identify culprit allergens and to closely follow changes in disease activity over time. Because allergy diagnosis is a complex and laborious multistep procedure, there is an urgent need for simpler but still functionally accurate ex vivo assays allowing objective diagnosis, substantiating treatment choices, and quantifying therapeutic responses. OBJECTIVE: In this study, we sought to develop a novel functional cell-based assay that relies on passive sensitization of allergic effector cells with patient serum, circumventing current limitations in allergy diagnosis. METHODS: We genetically engineered a conditional homeobox B8 (Hoxb8)-immortalized progenitor line from the bone marrow of mice that are transgenic for the human high-affinity IgE receptor (FcεRIα). These cells can be reproducibly differentiated into mature Hoxb8 mast cells within 5 days of culture in virtually unlimited numbers. RESULTS: We demonstrate that the established Hoxb8 mast cell assay can be used to accurately measure total IgE levels, identify culprit allergens, longitudinally monitor allergen-specific immunotherapy, and potentially determine the time point of tolerance induction upon allergen-specific immunotherapy in patients with allergy. To facilitate the analysis of large testing volumes, we demonstrate a proof-of-concept for a high-throughput screening application based on fluorescent cell barcoding using the engineered Hoxb8 mast cells. CONCLUSIONS: Our results indicate that this novel mast cell assay could represent a valuable tool to support clinicians in the identification of IgE-mediated allergies and in the quantification of treatment efficacy as well as duration of therapeutic response.

The mechanistic and functional profile of the therapeutic anti-IgE antibody ligelizumab differs from omalizumab.

Targeting of immunoglobulin E (IgE) represents an interesting approach for the treatment of allergic disorders. A high-affinity monoclonal anti-IgE antibody, ligelizumab, has recently been developed to overcome some of the limitations associated with the clinical use of the therapeutic anti-IgE antibody, omalizumab. Here, we determine the molecular binding profile and functional modes-of-action of ligelizumab. We solve the crystal structure of ligelizumab bound to IgE, and report epitope differences between ligelizumab and omalizumab that contribute to their qualitatively distinct IgE-receptor inhibition profiles. While ligelizumab shows superior inhibition of IgE binding to FcεRI, basophil activation, IgE production by B cells and passive systemic anaphylaxis in an in vivo mouse model, ligelizumab is less potent in inhibiting IgE:CD23 interactions than omalizumab. Our data thus provide a structural and mechanistic foundation for understanding the efficient suppression of FcεRI-dependent allergic reactions by ligelizumab in vitro as well as in vivo.

Eosinophils regulate adipose tissue inflammation and sustain physical and immunological fitness in old age.

Adipose tissue eosinophils (ATEs) are important in the control of obesity-associated inflammation and metabolic disease. However, the way in which ageing impacts the regulatory role of ATEs remains unknown. Here, we show that ATEs undergo major age-related changes in distribution and function associated with impaired adipose tissue homeostasis and systemic low-grade inflammation in both humans and mice. We find that exposure to a young systemic environment partially restores ATE distribution in aged parabionts and reduces adipose tissue inflammation. Approaches to restore ATE distribution using adoptive transfer of eosinophils from young mice into aged recipients proved sufficient to dampen age-related local and systemic low-grade inflammation. Importantly, restoration of a youthful systemic milieu by means of eosinophil transfers resulted in systemic rejuvenation of the aged host, manifesting in improved physical and immune fitness that was partially mediated by eosinophil-derived IL-4. Together, these findings support a critical function of adipose tissue as a source of pro-ageing factors and uncover a new role of eosinophils in promoting healthy ageing by sustaining adipose tissue homeostasis.