**Core Concept**
Interstitial nephritis is a form of kidney inflammation that affects the renal interstitium, the space between renal tubules. It can be caused by a variety of factors, including drugs, infections, and autoimmune disorders. The condition can lead to scarring of the kidneys and impaired renal function.

**Why the Correct Answer is Right**
The most common cause of interstitial nephritis is drug-induced injury. This is often due to the use of nonsteroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen and naproxen, which can cause direct toxicity to renal tubular cells. Other drugs, including antibiotics like penicillin and cephalosporins, can also induce interstitial nephritis through a hypersensitivity reaction. The exact mechanism is not fully understood, but it is thought to involve the release of pro-inflammatory cytokines and the activation of immune cells.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as it does not specify a particular cause of interstitial nephritis. While infections can cause the condition, they are not the most common cause.
**Option B:** This option is incorrect as it is too broad. Autoimmune disorders can cause interstitial nephritis, but they are not the most common cause.
**Option C:** This option is incorrect as it is not a specific cause of interstitial nephritis. While certain medications can cause the condition, the option does not specify which ones.

**Clinical Pearl / High-Yield Fact**
When considering a patient with interstitial nephritis, it is essential to review their medication list and discontinue any potential offending agents. This can help to alleviate symptoms and prevent further renal damage.

**Correct Answer: D. Drug-induced injury**