CD3-TCR complex
CD3δ
In addition to its role in activation, it is involved in the proper assembly of TCRs and their extracellular expression via the ERK (extracellular-regulated kinase) activation pathway, which is important for the positive selection of thymocytes.
CD3ε
It plays a role in regulating TCR expression, in thymic negative selection, and is a key component of cellular signalling.
CD3γ
It plays a role in cell activation, in the early assembly of the TCR, and in the regulation of its expression on the cell surface via the ERK (extracellular signal-regulated kinase) activation pathway.
CD3ζ
The ζζ dimer, CD247, has three ITAMs per chain and is involved in both cell activation and intrathymic differentiation.
ITAM (Immunoreceptor Tyrosine-based Activation Motif)
Cell signalling pathways which, through phosphorylation by specific tyrosine kinases, enable cell activation.
CD3
A molecule essential for the assembly and regulation of the TCR and for the activation of T lymphocytes. It consists of six chains: γ, δ, ε (two chains) and ζ (two chains).
TCR (T Cell Receptor)
It possesses specific binding sites in its variable region for antigens presented by cells via the MHC-TCR interaction, enabling specific recognition and functional activation of the cell to elicit an immune response. It consists of an α chain and a β chain; the latter can be classified as either β1 or β2.
CONTEXT/CLINICAL RELEVANCE
The diagnosis of T-cell neoplasms has benefited enormously from the development of antibodies directed against the constant region of the β chain (Cβ) of the TCR molecule, making it possible to analyse the distribution of the Cβ1 and Cβ2 populations and identify abnormalities that may indicate a disease.
This detection method is similar to the diagnostic model for B-cell neoplasia, which relies on the restriction of the membrane immunoglobulin light chains to either the kappa (κ) or lambda (λ) chains.
The simultaneous use of both antibodies (TCR Cβ1 and TCR Cβ2) ensures the correct and specific separation of the populations to accurately identify the relationship between the two populations.
In this way, it is possible to detect whether clonality is present, i.e. a complete or overwhelmingly predominant distribution towards a single type of β chain, which could be indicative of a T-cell neoplasm.
ANALYSIS STRATEGY
Example of an analysis strategy for a healthy donor (peripheral blood sample; clonality of helper T cells (CD4+) TCR Cβ2 detected).
In the case of T lymphocytes, the specific population is identified using anti-CD3 and the subpopulations are analysed according to whether they are TCR Cβ1 or TCR Cβ2. It is advisable to perform a more precise immunophenotyping, first separating the TCR α/β and TCR γ/δ populations, in order to subsequently identify TCR α/β subpopulations: CD4+/CD8- (helper T cells or Th), CD4-/CD8+ (cytotoxic T cells or Tc), CD4-/CD8- (double-negative T cells or DN) and CD4+/CD8+ (double-positive T cells or DP).
The TCR γ/δ T lymphocytes identified may also be analysed alongside the other auxiliary markers.
The use of auxiliary reagents allows for a more reliable and accurate diagnosis, as it provides detailed information on all possible populations and their exact quantification. It is appropriate to use TCR α/β, TCR γ/δ, CD4 and CD8 antibodies in combination with TCR Cβ1 and Cβ2, and other population markers (both T-cell-specific and non-specific) and maturation markers to detect aberrant or absent expression, thereby providing a more comprehensive and sensitive interpretation.