Hypereosinophilic syndrome: diagnosis and treatment:

Molecular and clinical rationale for therapeutic targeting of interleukin-5 and its receptor

Interleukin-5 is a Th2 homodimeric cytokine involved in the differentiation, maturation, migration, development, survival, trafficking and effector function of blood and local tissue eosinophils, in addition to basophils and mast cells. The IL-5 receptor (IL-5R) consists of an IL-5-specific α subunit that interacts in conformationally dynamic ways with the receptor's βc subunit, an aggregate of domains it shares with binding sites of IL-3 and granulocyte-macrophage colony-stimulating factor. IL-5 and IL-5R drive allergic and inflammatory immune responses characterizing numerous diseases, such as asthma, atopic dermatitis, chronic obstructive pulmonary disease, eosinophilic gastrointestinal diseases, hyper-eosinophilic syndrome, Churg-Strauss syndrome and eosinophilic nasal polyposis. Although corticosteroid therapy is the primary treatment for these diseases, a substantial number of patients exhibit incomplete responses and suffer side-effects. Two monoclonal antibodies have been designed to neutralize IL-5 (mepolizumab and reslizumab). Both antibodies have demonstrated the ability to reduce blood and tissue eosinophil counts. One additional monoclonal antibody, benralizumab (MEDI-563), has been developed to target IL-5R and attenuate eosinophilia through antibody-dependent cellular cytotoxicity. All three monoclonal antibodies are being clinically evaluated. Antisense oligonucleotide technology targeting the common βc IL-5R subunit is also being used therapeutically to inhibit IL-5-mediated effects (TPI ASM8). Small interfering RNA technology has also been used therapeutically to inhibit the expression of IL-5 in animal models. This review summarizes the structural interactions between IL-5 and IL-5R and the functional consequences of such interactions, and describes the pre-clinical and clinical evidence supporting IL-5R as a therapeutic target.

Churg-Strauss syndrome: evidence for disease subtypes?

PURPOSE OF REVIEW

Churg-Strauss syndrome (CSS) is a rare systemic small-vessel necrotizing vasculitis. Its main clinical characteristics, some potentially life-threatening, are now well known, as are its usual successive phases, from allergic rhinitis to asthma, and finally vasculitis. Conversely, physiopathogenetic mechanisms are not completely elucidated and clearly multiple, thereby suggesting the existence of different disease subtypes.

RECENT FINDINGS

Almost 40% of CSS patients have circulating antineutrophil cytoplasm autoantibodies (ANCAs), mostly directed against myeloperoxidase. ANCA-positive patients suffer more frequently from renal disease, peripheral nervous system involvement and/or alveolar hemorrhage, whereas frequent cardiac involvement, lung infiltrates and/or systemic manifestations are more common in those who are ANCA-negative. However, their respective global outcomes do not clearly differ. Patients might also be categorized according to other, more subtle clinical, radiological and/or biological parameters, for example, cardiac magnetic resonance imaging abnormalities or genetic background.

SUMMARY

Because of its practical and therapeutic repercussions, the priority remains the prompt, relatively easy identification of the most severely affected patients at CSS diagnosis, before searching for and trying to classify subsets. Large, collaborative studies are needed to determine whether other subgroups might be associated with outcomes and warrant different, and possibly new, therapeutic strategies.