**Core Concept**
Type 4 hypersensitivity reactions are a subset of delayed-type hypersensitivity reactions, which involve T-cell mediated immune responses. These reactions typically occur 48-72 hours after exposure to an antigen and are characterized by cell-mediated immunity.

**Why the Correct Answer is Right**
Granulomatous reactions are a classic example of type 4 hypersensitivity reactions. In these reactions, T-helper 1 (Th1) cells and macrophages work together to form granulomas, which are aggregates of immune cells that attempt to wall off and eliminate foreign substances or infectious agents. This process is often seen in diseases such as tuberculosis, sarcoidosis, and leprosy. The granulomatous reaction is a hallmark of type 4 hypersensitivity, as it involves a coordinated immune response to eliminate the offending agent.

**Why Each Wrong Option is Incorrect**
**Option A:** Serum sickness is an example of type 3 hypersensitivity reaction, which involves the formation of antigen-antibody complexes that deposit in tissues and cause inflammation.

**Option C:** Schürmann reaction is not a recognized term in immunology or microbiology. It's possible that this is a distractor or a typo.

**Option D:** Arthus reaction is another example of type 3 hypersensitivity reaction, which involves the formation of antigen-antibody complexes that deposit in tissues and cause inflammation.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that type 4 hypersensitivity reactions are characterized by a delayed onset (48-72 hours) and are often associated with cell-mediated immunity. This is in contrast to type 1 hypersensitivity reactions, which are immediate and involve IgE antibodies.

**✓ Correct Answer: B. Granulomatous reaction**