Belimumab Mechanism BLyS — SCE Rheumatology MCQ

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ModerateRheumatology PharmacologyBelimumab Mechanism BLySSCE Rheumatology

A 45-year-old woman with systemic lupus erythematosus has achieved good disease control with belimumab. During counselling, she asks how its mechanism differs from that of rituximab and anifrolumab. Which molecular target is bound directly by belimumab?

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Correct answer: C — Soluble B-lymphocyte stimulator (BLyS/BAFF)

Belimumab is a human IgG1 monoclonal antibody that binds soluble B-lymphocyte stimulator (BLyS), also termed BAFF or TNFSF13B. By preventing BLyS from engaging its receptors on B cells, it reduces survival of B cells, including autoreactive populations, and decreases differentiation into immunoglobulin-producing plasma cells. It does not bind B cells directly. IFNAR1 is targeted by anifrolumab, whereas CD20 is targeted by rituximab and other B-cell-depleting antibodies. Interleukin-6 receptor blockade is exemplified by tocilizumab, and complement C5 inhibition by eculizumab. The stored key was therefore correct, but the original option C contained an explanatory answer cue and was not parallel with the other options.

Reference: GlaxoSmithKline UK. Benlysta Summary of Product Characteristics, section 5.1 Pharmacodynamic properties: Mechanism of action. Text revised 2025. https://www.medicines.org.uk/emc/product/4679/smpc