**Core Concept:** Intravenous immunoglobulin (IVIG) is a preparation of pooled human immunoglobulins, obtained from plasma of thousands of blood donors, and is administered intravenously to patients with primary immunodeficiencies or autoimmune disorders. It works by replacing or augmenting the deficient immunoglobulins, which are proteins that help protect against infections.

**Why the Correct Answer is Right:** IVIG is primarily used in treating various primary immunodeficiencies (e.g., common variable immunodeficiency, Wiskott-Aldrich syndrome, X-linked agammaglobulinemia) and autoimmune disorders (e.g., Kawasaki disease, Guillain-Barré syndrome, systemic lupus erythematosus). It works by binding to the target pathogens, neutralizing them or modulating the host immune response, thereby preventing infections.

**Why Each Wrong Option is Incorrect:**

A. IVIG is not indicated in patients with secondary immunodeficiencies (e.g., HIV infection, cancer, corticosteroid therapy) as these patients require specific treatment modalities based on the underlying etiology.

B. IVIG is not used in patients with autoimmune diseases where the immune system is overactive and attacks the body's own tissues (e.g., rheumatoid arthritis, systemic sclerosis). It is contraindicated in such cases.

C. IVIG is not administered in patients with active bleeding disorders (e.g., hemophilia) as it may worsen the bleeding tendency.

D. IVIG is not used in patients with severe infections (e.g., sepsis, severe pneumonia) as it is not beneficial in treating acute infections.

**Clinical Pearl:** IVIG is a vital therapeutic tool in patients with primary immunodeficiencies and certain autoimmune disorders. However, its use should be judiciously tailored to the specific clinical scenario to ensure optimal patient outcomes and avoid potential complications.