**Core Concept**
Leukostasis, a complication of leukemia, occurs when a high white blood cell count (leukocytosis) leads to vascular occlusion and tissue ischemia. This condition can cause respiratory symptoms, including pain, pulmonary infiltrates, and pleural effusion, due to the release of inflammatory mediators and the accumulation of leukemic cells in the lungs.

**Why the Correct Answer is Right**
The patient's symptoms are likely caused by leukostasis, which is a direct result of the high white blood cell count. The release of inflammatory mediators, such as tumor necrosis factor-alpha (TNF-alpha) and interleukin-1 beta (IL-1β), contributes to the development of pulmonary infiltrates and pleural effusion. The leukemic cells accumulate in the lungs, causing vascular occlusion and tissue ischemia, which leads to pain and respiratory distress.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not directly relate to the patient's symptoms. While infection is a common complication of leukemia, it is not the primary cause of leukostasis and the associated respiratory symptoms.

**Option B:** This option is incorrect because it is a potential complication of leukemia treatment, but it is not the primary cause of the patient's symptoms. Radiation therapy can cause pulmonary fibrosis, but it does not directly lead to leukostasis and the associated respiratory symptoms.

**Option C:** This option is incorrect because it is a potential cause of respiratory symptoms in patients with leukemia, but it is not the primary cause of leukostasis. Infection can cause pulmonary infiltrates and pleural effusion, but it does not directly lead to the release of inflammatory mediators and the accumulation of leukemic cells in the lungs.

**Clinical Pearl / High-Yield Fact**
Leukostasis is a medical emergency that requires immediate treatment, including leukapheresis and corticosteroids, to reduce the white blood cell count and alleviate symptoms. Early recognition and treatment of leukostasis can improve patient outcomes and reduce the risk of complications.

**Correct Answer:** C.