HMB 45 is a marker for-
**Core Concept**
HMB-45 is a monoclonal antibody that recognizes an antigen present in melanocytic tumors, particularly those derived from melanocytes. It is used as a marker in immunohistochemistry to identify cells of melanocytic lineage.
**Why the Correct Answer is Right**
HMB-45 reacts with an antigen called gp100, which is a melanocyte-specific protein. This protein is present in the melanosomes of melanocytes and in melanoma cells, making HMB-45 a useful marker for identifying melanocytic lesions. The gp100 protein is involved in the processing and presentation of melanocyte-stimulating hormone (MSH) peptides, which play a crucial role in melanogenesis.
**Why Each Wrong Option is Incorrect**
**Option A:** HMB-45 is not a marker for lymphoid cells, as it is specific to melanocytes and melanoma cells.
**Option B:** While HMB-45 is a marker for melanocytic tumors, it is not specific to melanoma, as it can also react with other types of melanocytic lesions, such as spindle cell melanoma and melanocytic schwannoma.
**Option C:** This option is incomplete, please provide the actual distractor.
**Clinical Pearl / High-Yield Fact**
HMB-45 is a valuable marker in the differential diagnosis of melanocytic lesions, particularly when used in combination with other markers, such as S-100 and Melan-A.
**Correct Answer:** C. Melanocytes.