Thymocytes are T cell precursors which develop in the thymus. The processes of beta-selection, positive selection and negative selection shape thymocytes into a peripheral pool of T cells that are able to respond to foreign pathogens and are immunologically tolerant towards self antigens.

Thymocytes are classified into a number of distinct maturational stages based on the expression of cell surface markers. The earliest thymocyte stage is the double negative stage (negative for both CD4 and CD8), which more recently has been better described as Lineage-negative, and which can be divided into four substages. The next major stage is the double positive stage (positive for both CD4 and CD8). The final stage in maturation is the single positive stage (positive for either CD4 or CD8).

3F10

• recognized an antigen expressed both on thymocytes and non-lymphoid cells in the thymus. PMID: 10929055

20 alpha SDH

• can be used as an enzymatic marker to distinguish between subpopulations of activated T cells, which have not been previously detected by the conventional surface markers. PMID: 3501744

CD1

• a family of thymocyte differentiation antigens which consist of heavy chains with mol. wts between 43 and 49 kd binding to beta 2 microglobulin. PMID: 2583117
• immature (CD4+8+ double-positive) cortical thymocytes are the source of CD1 presentation for positive selection of NK1+ T cells. PMID: 7500054
• CD1+ thymocytes, under appropriate stimulations, display some of the functional capabilities of mature T cells. PMID: 1696526
• represents a family of MHC-related molecules, was analyzed on various human immature and mature thymocyte subpopulations. PMID: 2467935
• the CD1 surface marker delineates human thymocyte precursors and their products which lack, or possess, functional potential in vitro, on both alpha beta and gamma delta lineages. PMID: 2484962
• CD1 gene family encodes at least three proteins: CD1a, CD1b, and CD1c, which are coexpressed on cortical thymocytes and a number of T cell leukemias. PMID: 2701945
• a family of at least three components, CD1a, CD1b, and CD1c, that are characteristic of the cortical stage of thymocyte maturation. PMID: 2447586
• expressed on cortical thymocytes as well as on some lymphoid neoplasias. PMID: 3093894

CD1a

• expressed at high levels on mature (CD4+8-3+ and CD4-8+3+) human thymocytes, is therefore a useful marker of post-selection, post-thymic T-cell maturation. PMID: 7688345

CD2

• a thymocyte marker. PMID: 8629279

CD4

• Expressed on thymocyte subpopulations. PMID: 2783435
• play a decisive role in the differentiation of thymocytes. PMID: 2525172
• T cell surface glycoprotein. PMID: 7904343

CD5

• a phenotype characteristic of immature CD4-8+ thymocytes. PMID: 1840416

CD8

• Expressed on thymocyte subpopulations. PMID: 2783435
• Murine T cell surface antigen. PMID: 1799373
• expression on the surface of developing thymocytes is essential for the positive selection and maturation of CD8 single positive T cells. PMID: 8757613

CD25

• a marker for CD4+ thymocytes that prevent autoimmune diabetes in rats, but peripheral T cells with this function are found in both CD25+ and CD25- subpopulations. PMID: 10975823

CD26

• may play a role in thymic differentiation and maturation via the differential engagement of the CD3 pathway. PMID: 1717577
• also known as dipeptidyl peptidase IV (DPP IV) is a transmembrane 110- to 120-kDa serine aminopeptidase glycoprotein with multiple functions, including cellular trafficking through extracellular matrix, and costimulatory potential during T cell activation, and is an influence upon T cell differentiation during their maturation in the thymus. PMID: 9714693
• ontogenically controlled during T cell maturation and may play a role in thymic deletion of emerging clones. PMID: 8900475

CD45RA

• detected in all thymocyte subsets defined by CD4 and CD8 by using three-colour flow cytometry. PMID: 2279733

CD53

• a thymocyte selection marker whose induction requires a lower affinity TCR-MHC interaction than CD69, but is up-regulated with slower kinetics. PMID: 11867561

CD69

• transiently expressed on activated mature T cells and on thymocytes that are undergoing positive or negative selection in the thymus. PMID: 12039905
• discriminates MHC-dependent and -independent stages of thymocyte positive selection. PMID: 10201918

CD71

• a marker of immature, proliferating T cells. PMID: 7994765

CD150

• detected in T cells and in most thymocyte subsets, except CD4-8- cells. Surprisingly, the CD4-8- thymocytes of CD3gammadeltanull mice, but not of Ragnull or severe combined immunodeficiency mice, expressed CD150. PMID: 11486275

CTX (cortical thymocyte-specific antigen of Xenopus)

• a recently discovered T cell antigen whose expression is restricted to Xenopus cortical thymocytes, can serve as a differentiation surface marker of a population of immature thymocytes that appears to be the equivalent of the mammalian CD4/CD8 double-positive subset. PMID: 10323202
• a novel developmentally regulated type-I transmembrane protein is expressed specifically by a large fraction of cortical thymocytes in the amphibian Xenopus. PMID: 8625968
• cortical thymocyte marker of Xenopus. PMID: 15330258, PMID: 15199966
• a surface antigen whose expression in larval and adult Xenopus is primarily restricted to MHC class I-negative immature cortical thymocytes. PMID: 11246072
• a cortical thymocyte marker in Xenopus, is an immunoglobulin superfamily (Igsf) member comprising one variable and one constant C2-type Igsf domain, a transmembrane segment and a cytoplasmic tail. PMID: 9862345
• a developmentally regulated type I transmembrane protein of the immunoglobulin superfamily which, in the amphibian Xenopus, is exclusively expressed by a large fraction of cortical thymocytes and by different cell lines derived from independent spontaneous thymic tumors. PMID: 9281372
• a new Xenopus Ig superfamily molecule present on some cortical thymocytes and lymphoid tumor cells. PMID: 9188846

GIX

• The GIX antigen expressed on the thymocytes of GIX+ mice is a type-specific constituent of glycoprotein gp70, which forms the major envelope component of murine leukemia virus. PMID: 182895
• found on the thymocytes of some (GIX+) strains of mice, where its expression is controlled by two mendelian genes, Gv-1 and Gv-2. PMID: 180539

Granzymes

• The data suggest that (a) granzyme B is a pro-thymocyte marker for all T/NK lineage cells; (b) granzyme A transcripts are associated with thymocytes with the potential to develop into the CD8+ lineage; and (c) granzyme A enzymatic activity is only expressed in the most mature CD4-CD8+ stage, suggesting that granzyme proteins are not involved in early stages of thymocyte development. PMID: 7836927

H-2

• synthesis, initially most rapid in the mature cells, continued to be made at the highest rate in this thymocyte population. PMID: 7218802

H-2D

• expressed brightly on all subcapsular large cells, dimly on cortical small cells, and brightly on all migrants, cortisone-resistant thymocytes (CRT), and peripheral T cells. PMID: 6154739

HBA-71

• a new differentiation marker of human thymocytes. PMID: 2606935
• recognizes a Ewing's sarcoma associated antigen, which is also highly expressed on the cell surface of human cortical thymocytes and islets of Langerhans among normal tissues. PMID: 1656551
• In immunohistochemical staining the HBA-71 reacted with the cell surface of human cortical thymocytes. PMID: 2606935

ICT-1 antigen (thymocyte differentiation antigen)

• expressed in 50-70% of total thymocytes, but not in resting or PHA-activated peripheral blood T-cells and bone marrow cells. PMID: 7545548

IL-7

• a critical component of thymopoiesis in animals and has recently been shown to play an important role in T cell homeostasis. PMID: 12847229

Immature thymocyte antigen-1 (IMT-1)

• a novel thymocyte marker discriminating pre- and post-selected thymocytes. PMID: 9701033
• expressed on not only immature thymocytes of alpha beta T-cell lineage but also on those of gamma delta T-cell lineage. PMID: 10233677
• expressed during the late double negative (DN) stage as well as the early double positive (DP) stage of thymocyte maturation and suggest the possible involvement of IMT-1 in thymocyte differentiation. PMID: 7608536

J11d (heat-stable antigen)

• marks immaturity in thymocyte differentiation pathways. PMID: 8078424
• immature thymocyte marker. PMID: 1533011
• found in structurally heterogeneous forms on the surfaces of many types of murine hemopoietic cells. The extinction of expression of these antigens is associated with thymocyte maturation and Ig class switching in B cells, as well as terminal differentiation of macrophages. PMID: 2118158

JL1

• a 120 kDa cell surface glycoprotein, is a unique protein specifically expressed by immature double positive (DP) human thymocytes which are in the process of positive and negative selections through the interaction between thymocyte and antigen-presenting cells (APCs). PMID: 10672935

LFA-1 (lymphocyte function associated antigen-1) beta

• the beta-chain for LFA-1 is encoded on human chromosome 21, suggesting that trisomy 21 thymocytes may overexpress this adhesion molecule. PMID: 8099939
• an accessory molecule important in T-cell activation, is involved in thymocyte-epithelial cell binding, and contributes to the maturation of CD4-CD8- thymocytes to the CD4+CD8+ stage. PMID: 7927501

Ly-1/Ly-2

• Ly-1 plays a critical role in thymocyte proliferation, perhaps by serving as an IL 1-receptor. PMID: 3876939

Ly-2/3

• The major labeled thymocyte membrane protein consisting of disulfide-bonded subunits was identified as the Ly-2/3 antigen. PMID: 6270681

Ly-24 and Ly6C

• Use of the markers Ly-24, Ly6C, and 6B2 allows a subdivision of such progenitor thymocytes. PMID: 3257224

M241

• produced which binds to a human cell surface molecule with properties similar to the murine thymus leukemia (TL) antigen. This human TL-like antigen was found on thymocytes and some T cell lines derived from patients with acute lymphocytic leukemia, but was not found on peripheral blood lymphocytes or B cell lines. PMID: 6754387

MRC OX-2

• a membrane glycoprotein of about 45,000 Mr present on rat neurons, thymocytes, B cells, follicular dendritic cells, endothelium and smooth muscle. PMID: 2880589
• recognises antigens present on rat thymocytes, brain, follicular dendritic cells in lymphoid organs, vascular endothelium, some smooth muscle and B-lymphocytes. PMID: 6129975

Peanut agglutinin (PNA) receptor

• can be use to identify thymocyte subpopulations in the mouse. PMID: 6988508

Sca-1/Sca-2 (stem cell antigen)

• Both Sca-1 and Sca-2 were expressed on a sub-population of CD4-CD8- thymocytes, and this subpopulation was entirely contained within the Ly-1lo progenitor fraction of cells. Sca-1 expression by a phenotypically mature subset of CD4+CD8- thymocytes was also noted. Conversely, Sca-2 expression was observed on a phenotypically immature or nonmature subpopulation of CD4-CD8- thymocytes. Thus, expression of Sca-1 is observed throughout T cell ontogeny, whereas Sca-2 is expressed by some subsets of thymocytes, including at least one half of thymic blasts, but not by mature peripheral T lymphocytes. PMID: 2460547

T3 (OKT 3)

• mature thymocyte marker. PMID: 3102134, PMID: 3092215

T6 (OKT 6)

• immature thymocyte marker. PMID: 2970972, PMID: 3102134, PMID: 3092215
• can be detected on human cortical thymocytes and on dendritic cells in the skin by monoclonal antibodies. PMID: 3084948
• The human beta 2-microglobulin (beta-2m)-associated human thymocyte differentiation antigen. PMID: 6190941
• the human homologue of the murine thymus leukemia antigen (TL). PMID: 7033376, PMID: 7013988

TAP (T cell-activating protein)

• expressed on a small subset (10 to 20%) of thymocytes which is distinct from its expression on a majority (70%) of peripheral T lymphocytes. PMID: 2426356

THAM (thymocyte-activating molecule)

• highly expressed on CD4-CD8- murine thymocytes. PMID: 2461984

Thy-1

• distribution at the surface of isolated mouse thymocyte microdomains. PMID: 9284329
• triggers mouse thymocyte apoptosis through a bcl-2-resistant mechanism. PMID: 7906706
• the thymocyte Thy-1 would physiologically mediate cell-to-cell interactions among special subsets of lymphocytes under thymic influence. PMID: 6141204

Thy-1.1

• a marker for thymocyte maturation in transgenic mice. PMID: 1348881

Thy-2

• a minor cell-surface component which is present on the majority of thymocytes. PMID: 7009417

Thymic shared antigen-1 (TSA-1)

• a novel thymocyte marker discriminating immature from mature thymocyte subsets. PMID: 1531995
• expression level is the highest in most immature CD4- CD8- thymocytes, high in CD4+ CD8+ thymocytes, but barely detectable in mature CD4+ CD8- or CD4- CD8- thymocytes and peripheral T cells. PMID: 8642345
• a novel mouse thymocyte marker, may play a role during positive selection and the transition from CD4+CD8+ thymocytes to the mature CD4+CD8- and CD4-CD8+ subsets. PMID: 8258699

TL antigens (thymus leukaemia antigens)

• observed in the DP thymocytes of SCID-bg mice but not in their CD4-CD8- double negative (DN) fraction. PMID: 9429895
• encoded in the T region by T3 and T18 genes, is expressed primarily by intestinal epithelial cells and thymocytes. PMID: 7741975
• class I glycoproteins which are expressed on thymocytes and which are coded by the Tla region of the major histocompatibility complex of the mouse. PMID: 2427440

TL3

• expressed on 70 to 80% of subcapsular and cortical thymocytes, 30 to 40% of CRT, is undetectable on migrants but can be seen at low levels on 10 to 20% of spleen and lymph node T cells. PMID: 6154739

Other Thymocyte Markers

• Thymocyte subpopulations: an experimental review, including flow cytometric cross-correlations between the major murine thymocyte markers (Peanut agglutinin (PNA) receptor, Thy 1, H-2, TL, Ly 1 and Ly 2). PMID: 6362104
• The topographical relationships of Thy-1, Ly-1, Ly-2, and T200 were examined on the murine thymocyte. PMID: 6131095
• T1, 4, 5, 6, and 8, was expressed by a majority of thymocytes irrespective of the age of the fetal donor. PMID: 6607929