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CD45 is a transmembrane protein tyrosine phosphatase found on the surface of all nucleated hematopoietic cells, which is why it is used as a pan-leukocyte marker. This page is for researchers and lab staff who need to read “CD45 positive” or “CD45 negative” correctly and tell the CD45 isoform names apart. It is general reference information, not medical or diagnostic advice.
Short answer
CD45 (gene PTPRC, also called leukocyte common antigen, LCA) marks cells of the hematopoietic lineage that have a nucleus. It is absent from mature red blood cells and from plasma cells. Positive staining therefore points to a leukocyte or leukocyte-derived cell, while the strength and the isoform pattern depend on cell type and activation state.
Definition and scope
CD45 is an evolutionarily conserved receptor protein tyrosine phosphatase (EC 3.1.3.48) encoded by PTPRC on chromosome 1q31.3-q32.1. A 2018 review describes it as exclusively expressed on all nucleated cells of the hematopoietic system, with isoforms that are specific to cell type and to developmental or activation status (Rheinlaender, Schraven and Bommhardt, Immunol Lett 2018). A 1990 survey of leukemia and lymphoma cell lines likewise describes it as present on almost all hematopoietic cells except mature erythrocytes (Nakano et al., Acta Pathol Jpn 1990).
How CD45 works in practice
CD45 is essential for signaling through the T-cell and B-cell antigen receptors. It controls the Src family kinases Lck and Fyn; an early study showed that CD45 activates pp56lck by dephosphorylating Tyr-505 (Mustelin and Altman, Oncogene 1990). It also acts as a negative regulator of cytokine receptor signaling by suppressing JAK activity. CD45 deficiency causes T- and B-lymphocyte dysfunction presenting as severe combined immune deficiency, and the same review ties CD45 to autoimmune disease, cancer and infection. The review also cautions that it is unclear whether findings from rodent models apply to human CD45.
Names and isoforms
The gene has 34 exons. Exons 4, 5 and 6 (called A, B and C) are alternatively spliced, giving up to eight isoforms. Antibodies against the isoforms are used in immunohistochemistry to identify immune cell types.
| Name | What it refers to |
|---|---|
| CD45, LCA, PTPRC | The protein (leukocyte common antigen) and its gene; other aliases include LY5, T200 and GP180 |
| CD45RA | Isoform characteristic of naive T cells |
| CD45RO | Shortest isoform; characteristic of activated and memory T cells |
| CD45RABC | Longest form, about 200 kDa in T cells and about 220 kDa in B cells because of heavier glycosylation |
| B220 / CD45R | The name that came from the roughly 220 kDa B-cell form |
Source for the table: Wikipedia, PTPRC, read 2026-11-08.
What CD45 positive and negative mean
- Positive: the cell expresses CD45, consistent with a nucleated hematopoietic cell.
- Negative: consistent with cells outside this group, and specifically mature erythrocytes and plasma cells, which do not express it.
- Variable: within leukemia and lymphoma cell lines, expression depends on lineage and differentiation. In Nakano et al., six of six T-leukemic and five of five myeloid lines were stably positive, B-lineage lines varied with differentiation, only two of six histiomonocytoid lines were positive, and HTLV-I-associated T-cell lines did not express it.
- Isoform pattern: which isoform is present (RA, RO, RABC) carries information about cell type and activation, not just presence or absence.
Where it matters for labs
Because CD45 is on essentially every nucleated blood-lineage cell, it is a routine anchor for identifying leukocytes in immunophenotyping; the workflow around it is covered in PBMC preparation and staining for flow cytometry, and fluorochrome and viability considerations in flow cytometry dyes. Isoform antibodies are also used in histology to help separate lymphomas from carcinomas. In acute myeloid leukemia, CD45 colocalizes with lipid rafts on leukemic cells but not on non-transformed hematopoietic cells, and anti-CD45 antibody-drug conjugates have been proposed as an approach. For human immune cells in mice, see NSG mice; for stem-cell-derived cells, see induced pluripotent stem cells.
Common misunderstandings
- “CD45 positive means every immune cell.” It covers nucleated hematopoietic cells, but plasma cells and mature red cells lack it, and some leukemia and lymphoma lines are low or negative.
- “B220 is a different protein.” B220 is the B-cell form of CD45, named for its apparent size.
- “CD45RA and CD45RO are different genes.” They are alternatively spliced products of one gene, PTPRC.
- “Mouse results transfer directly.” Whether rodent CD45 findings apply to humans is described as unclear.
FAQ
What is CD45 a marker for?
It is a pan-leukocyte marker: it is expressed on all nucleated hematopoietic cells, with isoforms that vary by cell type and activation state.
What types of tumors are CD45 positive?
Leukemias and lymphomas are the hematopoietic tumors in which CD45 is relevant, but expression varies by lineage and differentiation (see the cell-line counts above). Isoform antibodies are used in immunohistochemistry to distinguish lymphomas from carcinomas. This page does not provide a tumor-by-tumor list or diagnostic guidance.
What is another name for CD45?
Leukocyte common antigen (LCA) and PTPRC. Other aliases are B220 or CD45R (the B-cell form), LY5, T200 and GP180.
Do all immune cells have CD45?
All nucleated hematopoietic cells express it, so effectively yes for leukocytes, but mature erythrocytes and plasma cells do not.
Sources
- Wikipedia, PTPRC, read 2026-11-08.
- Rheinlaender A, Schraven B, Bommhardt U. CD45 in human physiology and clinical medicine. Immunol Lett 2018;196:22-32. PubMed 29366662, doi:10.1016/j.imlet.2018.01.009, read 2026-11-08.
- Nakano A et al. Acta Pathol Jpn 1990;40(2):107-15. PubMed 2140233, read 2026-11-08.
- Mustelin T, Altman A. Oncogene 1990;5(6):809-13. PubMed 2141684, read 2026-11-08.
