Question

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

Answer 1

The specific interaction of TCRs with both MHC and peptide fragments ensures that T cells recognize antigens presented on host cells rather than free antigens, providing a targeted and effective immune response. The best answer to the student's question is option D.

Step-by-step explanation:

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 is unlike antibody recognition, which occurs independently of other host proteins. The TCR recognition ensures that T cells are focused on recognizing antigens associated with host cells and not those free in solution. The correct response to the question is option D: Ensure that TCRs are focused on recognizing antigens associated with host cells, and not those that are free in solution.

Antigen processing and presentation are key functions in the adaptive immune response. T cells, unlike antibodies, can only recognize processed antigens when these are presented on the cell surface by MHC molecules. Furthermore, T cells undergo clonal expansion upon recognition of specific antigens, ensuring an effective immune response. This process is facilitated by the specificity imparted by TCRs bound to MHC, targeting antigens directly processed by host cells, which prevents the recognition of 'self' and free-floating antigens. Therefore, the unique mechanism of TCR interactions with MHC and peptide ensures a precise and adequate adaptive immune response to pathogens within the host organism.

Answer 2

TCRs recognize peptide:MHC complexes to ensure antigens are associated with host cells, which differs from antibody recognition. Correct answer is 'D' to ensure focus on antigens associated with host cells.

Step-by-step explanation:

The T-cell receptors (TCRs) interaction with peptide:MHC complexes is crucial for T-cell activation, as TCRs recognize antigens presented by major histocompatibility complex (MHC) molecules on the surface of antigen-presenting cells. This recognition is different from antibodies, which can directly bind to antigens without the need for MHC presentation.

The fact that TCRs recognize components of both the MHC and the bound peptide ensures that TCRs are focused on recognizing antigens associated with host cells, rather than those that are free in solution. This has major implications for immune responses, as it helps secure that T cells only respond to antigens that have been processed and presented by host cells, preventing potential damage that could be caused by activated T cells. Based on the information provided, the correct answer to this question is D.

Ensure that TCRs are focused on recognizing antigens associated with host cells, and not those that are free in solution, as this is the reason TCRs recognize both MHC protein residues and residues within the pathogen-derived peptide.