**Core Concept**
Glucocorticoids, cyclosporine, and azathioprine are all immunosuppressant drugs used to prevent rejection in organ transplant patients and to treat autoimmune diseases. They work through different mechanisms to suppress the immune system, including reducing inflammation, inhibiting T-cell activation, and interfering with DNA synthesis.

**Why the Correct Answer is Right**
Cephalosporins are a class of antibiotics that work by inhibiting bacterial cell wall synthesis. They are not immunosuppressants and do not have a role in preventing transplant rejection or treating autoimmune diseases. The correct answer is Cephalosporin because it is the only option that does not belong to the category of immunosuppressive drugs.

**Why Each Wrong Option is Incorrect**
**Option A:** Glucocorticoids are potent immunosuppressants that reduce inflammation and inhibit T-cell activation, making them effective in preventing transplant rejection and treating autoimmune diseases.
**Option B:** Cyclosporine is a calcineurin inhibitor that prevents T-cell activation and proliferation, making it a crucial immunosuppressant in organ transplantation.
**Option D:** Azathioprine is a purine synthesis inhibitor that interferes with DNA synthesis, making it an effective immunosuppressant in preventing transplant rejection and treating autoimmune diseases.

**Clinical Pearl / High-Yield Fact**
When choosing an immunosuppressive agent, it is essential to consider the specific mechanism of action, potential side effects, and the patient's medical history to minimize the risk of adverse reactions.

**✓ Correct Answer: C. Cephalosporin**