The dendritic cell (DC) is presenting an antigen to a T cell but the T cell doesn’t recognize it. This is making the DC kind of sad.
In this case the DC is presenting the antigen on an MHC-I molecule and it is showing to a CD8 T cells. However, the T cell will recognize and respond to the antigen, only when if it is a specific antigen and it is bound to a particular MHC molecule. This process is called MHC restriction.
To learn more about antigen presentation and MHC restriction check out these links:
- Video: MHC Class I Processing
- Video: MHC Class II Processing
- Poster: Nature Immunology Antigen Processing
- Funny Comic by Pedromics: Presentation of the Antigen
- Immunobiology Book: The major histocompatibility complex and its functions
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Figure 5.16 T-cell recognition of antigens is MHC restricted
The antigen-specific T-cell receptor (TCR) recognizes a complex of antigenic peptide and MHC. One consequence of this is that a T cell specific for peptide x and a particular MHC allele, MHCa (left panel), will not recognize the complex of peptide x with a different MHC allele, MHCb (center panel), or the complex of peptide y with MHCa (right panel). The co-recognition of peptide and MHC molecule is known as MHC restriction because the MHC molecule is said to restrict the ability of the T cell to recognize antigen. This restriction may either result from direct contact between MHC molecule and T-cell receptor or be an indirect effect of MHC polymorphism on the peptides that bind or on their bound conformation.