One Striking Feature of TCR Interactions with Peptide:MHC Complexes Is

One striking feature of TCR interactions with peptide:MHC complexes is that amino acid residues in the MHC protein are as important to the TCR binding strength as are amino acid residues in the pathogen-derived peptide. This feature is in contrast to antigen recognition by antibodies, which is a direct interaction that is independent of other host proteins. Based on the different functions of T cells versus antibodies in the adaptive immune response, the fact that TCRs recognize components of both the MHC and the bound peptide exists to:

A) Prevent TCRs from binding only to surface exposed epitopes of native pathogens
B) Prevent immune evasion by a pathogen that has mutated the sequences required for antibody recognition
C) Put constraints on T cell recognition, due to the potentially damaging effector molecules made by activated T cells
D) Ensure that TCRs are focused on recognizing antigens associated with host cells, and not those that are free in solution
E) Ensure that the pathogen has already been destroyed by the host cell before the T cell will recognize it