Would you tell me what it is (cd4+ T-cell populations)?
It is a population of T-cell that express CD4 receptor on its surface.
The CD4 molecule recognizes MHCII, which is a molecule that presents peptides from outside of the cell. The T-cell receptor (TCR) recognizes the peptide presented by the MHCII. Together the CD4 and the TCR are able to relay a signal into the cell and stimulate the T-cell.
There are also cells that are CD8+, which means that they recognize MHCI. MHCI presents peptides from inside the cell, for instance when a cell is infected with a virus or by a bacterial lysteria infection.
Immature thymocytes are CD4+ and CD8+, when they leave the thymus they are either CD4+ or CD8+.
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