**Core Concept:** Acute exacerbation of ulcerative colitis is typically managed with immunosuppressive agents due to its inflammatory nature. In severe cases, corticosteroids can be considered.

**Why the Correct Answer is Right:** The correct answer, **D**. Mesalamine, is a top choice for the management of ulcerative colitis, particularly in milder to moderate cases. It acts as a local anti-inflammatory agent, inhibiting cellular and humoral immune responses within the intestinal mucosa, thereby reducing inflammation and alleviating symptoms.

**Why Each Wrong Option is Incorrect:**

A. **Option A (Methotrexate):** Although Methotrexate is an immunosuppressive agent, it is generally reserved for severe cases of ulcerative colitis where other treatments have failed. Its systemic absorption can lead to potential side effects.

B. **Option B (Tacrolimus):** Tacrolimus is typically used for organ transplantation and is not a first-line choice for managing ulcerative colitis. Its immunosuppressive properties may increase the risk of infections and malignancies.

C. **Option C (Corticosteroids):** Corticosteroids, such as Prednisolone, are used in severe cases where local anti-inflammatory agents, like mesalamine, are insufficient. However, their long-term usage can lead to significant side effects.

**Clinical Pearl:** In severe cases of ulcerative colitis, a combination of local (e.g., mesalamine) and systemic (e.g., corticosteroids) treatments may be necessary to effectively manage symptoms and prevent complications, but usage should be discontinued as soon as possible to avoid side effects.