Which receptor does Benralizumab act on?

Explanation

## Correct Answer: B. IL-5 Benralizumab is a monoclonal antibody that acts as an **IL-5 receptor antagonist** (specifically targeting the IL-5 receptor alpha subunit on eosinophils). It is used in the treatment of **severe eosinophilic asthma** and **eosinophilic granulomatosis with polyangiitis (EGPA)**. The drug works by binding to the IL-5 receptor on eosinophils, preventing IL-5 signaling and leading to eosinophil apoptosis and depletion. This mechanism is critical because IL-5 is the primary cytokine responsible for eosinophil recruitment, activation, and survival. In Indian clinical practice, benralizumab is increasingly recognized as a biologic agent for severe asthma phenotypes with elevated eosinophil counts (typically >300 cells/μL). Unlike mepolizumab (which binds IL-5 directly) and reslizumab (which also targets IL-5), benralizumab uniquely targets the receptor itself, making it more potent in eosinophil depletion. The drug has shown efficacy in reducing exacerbations and oral corticosteroid dependence in Indian asthma cohorts, particularly in patients with eosinophilic phenotypes. ## Why the other options are wrong **A. IL-4** — IL-4 is a Th2 cytokine involved in IgE production and allergic inflammation, but it is NOT the target of benralizumab. IL-4 receptor antagonists are not used for eosinophilic asthma. This is a distractor that confuses the broader Th2 pathway with the specific eosinophil-targeting mechanism of benralizumab. **C. IL-1** — IL-1 is a pro-inflammatory cytokine involved in innate immunity and systemic inflammation, not eosinophil-specific pathways. IL-1 antagonists (like anakinra) are used in autoinflammatory conditions, not asthma. This option represents a fundamental misunderstanding of the eosinophil-specific biology that benralizumab targets. **D. TNF-α** — TNF-α is a key pro-inflammatory cytokine targeted by agents like infliximab and adalimumab in autoimmune diseases, but it is not the mechanism of benralizumab. This is an NBE trap pairing a well-known monoclonal antibody target with an incorrect cytokine, testing whether students confuse different biologic mechanisms. ## High-Yield Facts - **Benralizumab** is an IL-5 receptor alpha antagonist (not IL-5 direct binder like mepolizumab). - Mechanism: binds IL-5Rα on eosinophils → eosinophil apoptosis and depletion. - Indication: **severe eosinophilic asthma** with blood eosinophils ≥300 cells/μL (Indian guidelines align with GINA). - Also approved for **EGPA (eosinophilic granulomatosis with polyangiitis)** in India. - Dosing: 30 mg SC every 4 weeks for 3 doses, then every 8 weeks (Indian practice). - Reduces oral corticosteroid dependence and asthma exacerbations in eosinophilic phenotypes. ## Mnemonics **BEN = Eosinophil Receptor** **BEN**ralizumab → **E**osinophil **N**eutralizer (targets IL-5 receptor on eosinophils). Use when distinguishing benralizumab from mepolizumab (which binds IL-5 ligand directly). **IL-5 Axis Agents** **MEpo** (Mepolizumab) = IL-5 ligand binder; **BEN** (Benralizumab) = IL-5 **R**eceptor binder; **RES** (Reslizumab) = IL-5 ligand binder. Benralizumab is the only receptor antagonist in this trio. ## NBE Trap NBE pairs benralizumab with TNF-α (option D) because both are monoclonal antibodies used in chronic inflammatory diseases, testing whether students conflate different biologic mechanisms rather than knowing the specific cytokine target of each agent. ## Clinical Pearl In Indian asthma clinics, benralizumab is increasingly preferred over mepolizumab in eosinophilic asthma because its receptor-targeting mechanism achieves faster and more complete eosinophil depletion, translating to quicker symptom control and reduced steroid burden—critical in resource-limited settings where oral corticosteroid side effects are a major concern. _Reference: KD Tripathi Pharmacology Ch. 27 (Immunosuppressants & Biologics); Harrison Ch. 333 (Asthma)_