This is determined by the major histocompatibility complex (MHC) proteins on its surface: The endocytosed antigen is cut up into peptides, which can then be bound on the MHC complexes, depending on whether they display the sequence characteristics required for binding to the MHC: peptide length, anchor residue etc.

Thanks for your reply!

You have explained that MHC I & II tend to present peptides with specific lengths, 8-10 AA and 13-18, respectively.

However, there are numerous peptide candidates that meet the length requirement, how does the MHC decide which one to present to TCR?

https://www.sciencedirect.com/topics/immunology-and-microbiology/antigen-presentation

The length alone is not sufficient, the sequence of the peptide determines the affinity of the peptide to the MHC (

Article Peptide binding by class I and class II MHC molecules

)

Answer

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