**Core Concept**
Tacrolimus is a calcineurin inhibitor that plays a crucial role in immunosuppression. It is used to prevent organ rejection in transplant patients. By inhibiting calcineurin, tacrolimus disrupts the activation of T-lymphocytes, which are essential for the immune response. This action results in reduced production of cytokines, including interleukin-2 (IL-2).

**Why the Correct Answer is Right**
Tacrolimus binds to FKBP-12, a cytosolic protein, forming a complex that inhibits the phosphatase activity of calcineurin. This inhibition prevents the dephosphorylation and subsequent translocation of nuclear factor of activated T-cells (NFAT) into the nucleus. NFAT is essential for the transcription of IL-2 gene. Therefore, by inhibiting calcineurin, tacrolimus indirectly inhibits the transcription of IL-2. This dual mechanism of action, involving both calcineurin inhibition and IL-2 transcription inhibition, is responsible for the immunosuppressive effects of tacrolimus.

**Why Each Wrong Option is Incorrect**
**Option A:** Inhibition of transcription of IL 2 - While tacrolimus does inhibit IL-2 transcription, this option is incomplete as it does not mention the role of calcineurin inhibition.
**Option B:** Inhibition of translation of IL 2 - Tacrolimus does not directly inhibit the translation of IL-2. Its mechanism of action involves transcriptional regulation through calcineurin inhibition.
**Option C:** Inhibition of calcineurin - While this is a correct aspect of tacrolimus' mechanism of action, option D is more comprehensive as it includes the inhibition of IL-2 transcription.

**Clinical Pearl / High-Yield Fact**
Tacrolimus is known for its narrow therapeutic index, and its levels must be carefully monitored to avoid nephrotoxicity and other adverse effects. It is often used in combination with other immunosuppressive agents to prevent organ rejection in transplant patients.

**✓ Correct Answer: D. Both 'a' and 'c'**