**Core Concept**
The L.E. Cell phenomenon is a laboratory test used to diagnose systemic lupus erythematosus (SLE), an autoimmune disease characterized by the presence of antinuclear antibodies (ANA). The test involves the ingestion of neutrophils by macrophages, leading to the formation of a neutrophil with a characteristic "bite" or "phagocytic" appearance.

**Why the Correct Answer is Right**
The L.E. Cell phenomenon is a result of the immune complex deposition and subsequent activation of the complement system, leading to the formation of neutrophil-antibody complexes. These complexes are then phagocytosed by macrophages, resulting in the characteristic L.E. Cell appearance. The presence of these cells in the peripheral blood is a diagnostic indicator of SLE.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because the L.E. Cell phenomenon is not typically seen in rheumatoid arthritis, which is another autoimmune disease. While both conditions share some similarities, the L.E. Cell phenomenon is a specific indicator of SLE.
* **Option B:** This option is incorrect because the L.E. Cell phenomenon is not a characteristic feature of scleroderma, which is a different autoimmune disease. Scleroderma is characterized by fibrosis and vascular damage, rather than the immune complex deposition seen in SLE.
* **Option C:** This option is incorrect because the L.E. Cell phenomenon is not typically seen in infections, which can cause a variety of laboratory abnormalities but are not associated with the characteristic L.E. Cell appearance.

**Clinical Pearl / High-Yield Fact**
The L.E. Cell phenomenon is a classic example of a laboratory test that can be used to diagnose an autoimmune disease. However, it's essential to note that the test is not 100% specific for SLE and can be seen in other conditions. Therefore, a positive result should be interpreted in conjunction with other clinical and laboratory findings.

**Correct Answer:** D.