**Core Concept**
Kostmann's syndrome, also known as severe congenital neutropenia, is a rare genetic disorder characterized by a significant reduction in the production of neutrophils, a type of white blood cell essential for fighting bacterial infections. This condition leads to recurrent severe bacterial infections due to an impaired immune response.

**Why the Correct Answer is Right**
The treatment for Kostmann's syndrome involves administering granulocyte colony-stimulating factor (G-CSF) to stimulate the production of neutrophils. G-CSF works by binding to its receptor on the surface of hematopoietic cells, triggering a signaling cascade that leads to the release of mature neutrophils from the bone marrow into the bloodstream. This helps to restore the patient's immune function and reduce the frequency and severity of infections.

**Why Each Wrong Option is Incorrect**
* **Option A:** This is incorrect because antibiotics are not a suitable treatment for Kostmann's syndrome, as they do not address the underlying cause of the condition.
* **Option B:** This is incorrect because immunoglobulin replacement therapy is used to treat primary immunodeficiency disorders, not Kostmann's syndrome.
* **Option C:** This is incorrect because antifungal medications are used to treat fungal infections, which are not the primary concern in Kostmann's syndrome.

**Clinical Pearl / High-Yield Fact**
Kostmann's syndrome is a rare but severe form of neutropenia that can be life-threatening if left untreated. Early diagnosis and treatment with G-CSF can significantly improve patient outcomes and reduce the risk of complications.

**Correct Answer: C. G-CSF.