CD-99 is for
**Question:** CD-99 is for
A. CD40 ligand
B. CD56
C. CD3
D. CD138
**Core Concept:**
CD99 is a cell surface glycoprotein that is expressed on various cell types, including hematopoietic cells, skeletal muscle cells, and some tumor cells. It is part of the MHC class I-like protein family and plays a role in cell adhesion, signaling, and immune response modulation.
**Why the Correct Answer is Right:**
CD99 is primarily associated with the expression on hematopoietic cells, particularly myeloid lineage cells, such as monocytes, granulocytes, and mast cells. It is also expressed on some tumor cells, particularly those originating from myeloid or lymphoid lineages.
**Why Each Wrong Option is Incorrect:**
A. CD40 ligand is a soluble protein involved in the activation of B cells and T cells, not CD99.
B. CD56 is a cell surface glycoprotein found on natural killer (NK) cells, some T cells, and hematopoietic stem cells, not CD99.
C. CD3 is a protein complex found on the surface of T cells, not CD99.
**Clinical Pearl:**
CD99 is often used as a marker for certain tumors, particularly acute myeloid leukemia (AML) and Ewing's sarcoma. Its overexpression can be indicative of these malignancies, facilitating differential diagnosis.
**Correct Answer:**
D. CD138
CD99 is associated with CD138, which is also known as syndecan-1. CD138 is a transmembrane protein involved in cell adhesion and signaling, similar to CD99. Its expression is also seen in certain hematopoietic cells, similar to CD99, but it is typically expressed in other types of tumors as well, making it less specific than CD99 for diagnosing specific malignancies.