CD marker of histiocytosisis:
**Core Concept**
The question is testing the knowledge of specific CD markers associated with histiocytosis, a group of rare disorders characterized by abnormal proliferation of histiocytes, a type of immune cell. The correct CD marker for histiocytosis is a crucial diagnostic tool in histopathology.
**Why the Correct Answer is Right**
The correct answer is CD68, also known as KP1, which is a glycoprotein expressed on the surface of histiocytes, including Langerhans cells, macrophages, and monocytes. CD68 is a useful marker in the diagnosis of histiocytic disorders, including Langerhans cell histiocytosis (LCH), a type of histiocytosis that can affect various organs, including the bone marrow, liver, spleen, and central nervous system. The expression of CD68 is a key feature of histiocytes and helps distinguish them from other types of immune cells.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because CD1a is a marker for Langerhans cells, but it is not specific to histiocytosis. While CD1a is expressed on Langerhans cells, it is also found on other types of immune cells.
**Option B:** This option is incorrect because CD14 is a marker for monocytes and macrophages, but it is not specific to histiocytosis. While CD14 is expressed on monocytes and macrophages, it is also found on other types of immune cells.
**Option C:** This option is incorrect because CD45 is a marker for leukocytes, but it is not specific to histiocytosis. While CD45 is expressed on all leukocytes, it is not a specific marker for histiocytes.
**Clinical Pearl / High-Yield Fact**
CD68 is a useful marker in the diagnosis of histiocytic disorders, including Langerhans cell histiocytosis (LCH). In addition to CD68, other markers, such as CD1a and S-100 protein, can also be used to support the diagnosis of LCH.
**Correct Answer:** C. CD68.