CD45bright

CD45bright is a term used in flow cytometry to describe cells that exhibit high surface expression of CD45, a receptor-type protein tyrosine phosphatase also known as the leukocyte common antigen. CD45 is expressed on all nucleated hematopoietic cells, and the level of CD45 staining can be used to distinguish leukocyte subpopulations by fluorescence intensity. In typical human peripheral blood samples, lymphocytes are characterized as CD45bright, whereas monocytes and granulocytes are more often CD45dim, reflecting lower surface density of CD45 or differences in cell size and granularity. However, exact intensity can vary with sample preparation, instrument settings, antibody clone, and fluorochrome, so gating is relative to the assay.

CD45 exists in multiple isoforms, such as CD45RA, CD45RB, CD45RC, and CD45RO, produced by alternative splicing. These isoforms reflect cell lineage and activation state, particularly among T cells, but the descriptor CD45bright refers to overall expression level rather than a specific isoform.

In clinical and research flow cytometry, CD45bright populations are often used to gate lymphocytes before further analysis of surface markers (e.g., CD3, CD19, CD56). The CD45 brightness criterion helps separate leukocytes from debris and from other cell types and can aid in detection of abnormal populations in hematologic malignancies or immune disorders. Limitations include variable staining intensity and instrument differences, requiring appropriate controls and compensation.