This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Immunomodulatory: DMARDS, Monoclonal Antibodies, Subject name: Pharmacology
Donesumab, a monoclonal antibody against RANK ligand is used for the treatment of: 
Select and explain. 
A. Rheumatoid arthritis, B. Osteoporosis, C. Osteoarthritis, D. Systemic lupus erythematosis
B: Osteoporosis
Answer: B: Osteoporosis 
Explanation: Ans. (B) Osteoporosis(Ref: Principles of pharmacolpg HL Sharma and KK Sharma 2007/641)Receptor for activated nuclear factor kB (RANK) is present on osteoclast progenitors. Binding of RANK-ligand to these receptors causes differentiation and activation of osteoclast progenitors to mature osteoclasts. Donesumab is a monoclonal antibody that prevents the binding of RANK-ligand with RANK. This prevents activation of osteoclasts and it can therefore, be used in osteoporosis.Osteoblasts synthesize and release osteoprotegerin (OPG), identical with RANK, which functions as a 'decoy receptor'. OPG, thus inhibits the binding to RANK-L to RANK. Hence OPG analogs can be the potential therapeutic agents of osteoporosis.