**Core Concept**
Secondary granules in neutrophils are a type of cytoplasmic granule that plays a crucial role in the inflammatory response and immune function. These granules are formed in the promyelocyte stage of neutrophil development and are rich in enzymes and antimicrobial proteins.

**Why the Correct Answer is Right**
Secondary granules are involved in the degradation of extracellular matrix and the killing of ingested microorganisms. They contain enzymes such as lactoferrin, cathepsin G, and defensins, which are essential for the neutrophil's antimicrobial activity. The formation and function of secondary granules are regulated by specific transcription factors and signaling pathways.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because primary granules are the first type of granule to be formed in neutrophils and contain myeloperoxidase, not secondary granules.
**Option B:** This option is incorrect because azurophilic granules are a type of primary granule that contains myeloperoxidase and other antimicrobial enzymes, not secondary granules.
**Option C:** This option is incorrect because gelatinase granules are a type of secondary granule that contains matrix metalloproteinases, but this is not the only type of secondary granule.

**Clinical Pearl / High-Yield Fact**
Neutrophils play a crucial role in the innate immune response, and their granules are essential for the degradation of extracellular matrix and the killing of ingested microorganisms. Understanding the composition and function of neutrophil granules is critical for the diagnosis and treatment of various inflammatory and infectious diseases.

**Correct Answer: D. Gelatinase granules**