CD45dim

CD45dim refers to cells that express relatively low levels of CD45, the leukocyte common antigen encoded by the PTPRC gene. CD45 is a protein tyrosine phosphatase receptor found on nearly all nucleated hematopoietic cells, and its expression level is commonly used in flow cytometry to differentiate leukocyte populations.

In flow cytometry analysis, CD45 expression is often used together with light-scatter properties to identify and gate cell populations. Lymphocytes typically appear CD45bright, monocytes CD45intermediate, and granulocytes or certain blast populations can be CD45dim relative to lymphocytes. The label CD45dim is therefore a descriptive term indicating lower CD45 expression compared with surrounding or reference leukocytes within the same sample, and its interpretation depends on instrument settings, antibody clone, and fluorochrome brightness.

CD45dim is frequently observed in specific contexts, such as identifying abnormal or malignant cell populations (for example, blasts in acute leukemias) or distinguishing granulocytes from lymphocytes in diagnostic panels. It is not a distinct cell type but a phenotype used to classify cells during immunophenotyping, often in combination with additional markers (such as CD3, CD19, CD14, CD15, HLA-DR) to determine lineage and maturation state.

Limitations include variability in instrument sensitivity and staining protocols, which can affect the perceived brightness of CD45. Hence, CD45dim interpretation should consider assay design and appropriate controls. See also CD45 and flow cytometry immunophenotyping.