CD4+ T cell
CD8+ T cell
T cells are one of the pillars of adaptive immunity. They participate in the so-called cellular immunity. Although they cannot be dissociated morphologically, we distinguish between CD4+ and CD8+ T cells which have very different functions.
Haematopoiesis / cytology
Cytology characteristics and the main principles of T cell ontogeny are described here.
If the morphology of CD4+ and CD8+ T lymphocytes does not allow them to be distinguished, flow cytometry makes it possible to identify clusters of differentiation (CDs), and in particular CD4 and CD8 which make it possible to divide T cells into these two very different families on a functional level.
Functions
Common features of CD4+ and CD8+ T Cells
- Antigen recognition
- Maturation
- Activation
The antigen is recognised if and only if it is embedded in an HLA molecule. It should be noted that only antigens of a protein nature and cleaved into very small fragments (peptides) can be embedded in HLA molecules to then be presented to lymphocytes.
T cells undergo a maturation process through which they acquire their TCR (see T cell ontogeny).
CD8+ and CD4+ T cells are activated in the same way by the dendritic cell (see T cell activation).
Differences between CD4+ and CD8+ T cells
| | CD8+ T cells | CD4+ T cells |
|---|---|---|
| Name | Cytotoxic T cells (CTL) | T helper (Th) cells = Helper T cells |
| Co-receptor | CD8 | CD4 |
| Interaction | Class I HLA | Class II HLA |
| Peptides recognised | Endogenous (and exogenous by cross-presentation carried out by the dendritic cells) | Exogenous |
| Functions | Cytotoxiciy | Cell cooperation with CD8+ T cells and B cells |
| Effector mechanisms | Perforin/granzyme Fas – Fas-Ligand TRAIL | Cytokine synthesis (Th1, Th2, Th17 profiles) |
What should be remembered
T cells include CD4+ and CD8+ T cells, which are two very heterogeneous populations in terms of functions. Their involvement in allorecognition mechanisms on the one hand, and the cytotoxic functions of CD8+ T cells on the other hand, are essential in organ transplantation, which is why they constitute the preferred target of current immunosuppressants.
