# DBT JRF 2020 — Question 74

Exam: DBT JRF 2020 · Section: B · Topic: Immunology · Difficulty: Medium

## Question

Cyclosporine, an immunosuppressive drug, given to avoid transplant rejection acts by

## Options

- **A.** B cell inhibition
- **B.** complement inhibition
- **C.** T cell inhibition
- **D.** NK cell inhibition

## Answer

Option C

## Explanation

Cyclosporine A (CsA) mechanism of immunosuppression: CsA binds to cyclophilin (CypA, a cytoplasmic immunophilin/peptidyl-prolyl isomerase). The CsA-cyclophilin complex inhibits calcineurin (protein phosphatase 2B, PP2B), a calcium/calmodulin-dependent phosphatase. Calcineurin normally dephosphorylates NFAT (Nuclear Factor of Activated T cells), allowing it to translocate to the nucleus and activate IL-2 transcription. By blocking calcineurin → NFAT remains phosphorylated (cytoplasmic) → IL-2 not produced → T cells cannot proliferate (T cell activation suppressed). Tacrolimus (FK506) has the same mechanism but binds FKBP12 instead of cyclophilin. CsA is used to prevent allograft rejection and treat autoimmune diseases.

Source: https://mypyqbuddy.com/questions/cyclosporine-an-immunosuppressive-drug-given-to-avoid-transplant-6a05a8a02adafec470293262