Correct Answer: B. IL-2 receptor antagonist
Basiliximab is a chimeric monoclonal antibody that selectively binds to the IL-2 receptor (CD25) on the surface of activated T lymphocytes, blocking the high-affinity IL-2 receptor and preventing IL-2-mediated T-cell proliferation. This mechanism makes it an IL-2 receptor antagonist, not an inhibitor of TNF or other cytokines. In Indian clinical practice, basiliximab is primarily used as an induction immunosuppressant in organ transplantation (kidney, heart, liver) to prevent acute rejection episodes. It is administered as an intravenous bolus on days 0 and 4 post-transplant, reducing the incidence of acute cellular rejection by approximately 30–40%. Unlike polyclonal antibodies (e.g., ATG) or anti-CD3 agents (e.g., OKT3), basiliximab has a more selective mechanism targeting only activated T cells expressing CD25, resulting in fewer systemic side effects and lower rates of cytokine release syndrome. According to KD Tripathi and standard transplant protocols followed in Indian centres, basiliximab is classified as a T-cell-specific immunosuppressant and is often combined with calcineurin inhibitors, mycophenolate, and corticosteroids in triple or quadruple immunosuppressive regimens post-transplant.
Why the other options are wrong
A. TNF inhibitor — This is wrong because basiliximab does not inhibit TNF-α. TNF inhibitors (infliximab, adalimumab, etanercept) are used in autoimmune diseases like rheumatoid arthritis and inflammatory bowel disease. Basiliximab's mechanism is entirely different—it blocks IL-2 signalling on T cells, not TNF pathways. NBE may trap students who confuse all monoclonal antibodies as having similar mechanisms. C. Anti-CD3 antibody — This is wrong because basiliximab targets CD25 (IL-2 receptor), not CD3. Anti-CD3 antibodies (OKT3, muromonab) bind directly to the T-cell receptor complex and cause pan-T-cell depletion, leading to severe cytokine release syndrome and systemic effects. Basiliximab is more selective and safer. NBE may confuse students who remember both are monoclonal antibodies used in transplantation. D. IL-1 receptor antagonist — This is wrong because basiliximab blocks IL-2 receptors, not IL-1 receptors. IL-1 receptor antagonists (anakinra, canakinumab) are used in autoinflammatory conditions and gout. Basiliximab's target is the IL-2 receptor on activated T lymphocytes. This is a distractor testing whether students can distinguish between different interleukin receptor antagonists.
High-Yield Facts
- Basiliximab is a chimeric monoclonal antibody targeting CD25 (IL-2 receptor) on activated T cells.
- Induction immunosuppression in organ transplantation: basiliximab given on days 0 and 4 post-transplant reduces acute rejection by 30–40%.
- Selective mechanism: basiliximab only blocks IL-2-mediated T-cell proliferation in activated lymphocytes, sparing resting T cells and innate immunity.
- Lower toxicity profile compared to anti-CD3 (OKT3) and polyclonal antibodies (ATG); minimal cytokine release syndrome.
- Combination therapy: basiliximab is used with calcineurin inhibitors, mycophenolate, and corticosteroids in post-transplant immunosuppressive regimens.
Mnemonics
IL-2 Receptor Antagonists: BAS-IL-IX BASiliximab → IL-2 receptor → IX (Roman numeral for 9, memory hook for 'induction'). Basiliximab = IL-2 receptor blocker used for induction in transplant. Use this when differentiating basiliximab from TNF inhibitors or anti-CD3 agents. Monoclonal Antibodies in Transplant: CD-25 vs CD-3 CD-25 = Basiliximab (selective, safer, induction). CD-3 = OKT3/Muromonab (pan-T-cell, severe CRS, rescue). Remember: Basiliximab is the 'gentle' antibody; OKT3 is the 'nuclear option'. Use when comparing induction agents.
NBE Trap
NBE pairs basiliximab with other monoclonal antibodies (anti-CD3, TNF inhibitors) to test whether students understand that mechanism of action differs by target receptor, not just by antibody class. Students who memorize "basiliximab = monoclonal antibody used in transplant" without knowing its IL-2 receptor specificity will fall into the anti-CD3 trap.
Clinical Pearl
In Indian transplant centres, basiliximab is preferred over OKT3 for induction because it causes fewer cytokine-mediated side effects (fever, chills, hypotension) in post-operative patients who are already haemodynamically compromised. A patient receiving basiliximab on day 0 and day 4 post-renal transplant will have selective IL-2 blockade without the systemic inflammation seen with anti-CD3 agents.
_Reference: KD Tripathi Pharmacology Ch. 76 (Immunosuppressants); Harrison Ch. 135 (Transplantation)_