Ch 4 Antigen Recognition in the Adaptive Immune System Flashcards
What are the functionally distinct domains (regions) of antibody and TCR molecules? What features of the amino acid sequences in these regions are important for their functions?
Antibody and T cell receptor (TCR) chains contain variable domains that are involved in antigen recognition and constant domains that, in the case of antibodies, mediate effector functions. Variable domains contain residues that contribute to antigen recognition.
What are the differences in the types of antigens recognized by antibodies and TCRs?
Antibodies can recognize all types of molecules, including small molecules, proteins, carbohydrates, lipids, and nucleic acids. In proteins, antibodies can recognize conformational or linear epitopes. TCRs can recognize only linear peptides bound to the clefts of MHC molecules.
What mechanisms contribute to the diversity of antibody and TCR molecules? Which of these mechanisms contributes the most to the diversity?
The joining of segments of antibody and TCR genes in developing lymphocytes, known as VDJ recombination, is responsible for the diversity of antibodies and TCRs. Variations in nucleotide sequences introduced by the use of different V, D, and J segment combinations (combinatorial diversity) and during VDJ joining (junctional diversity) contribute to diversity, but junctional alterations make the largest contribution.
What are some of the checkpoints during lymphocyte maturation that ensure survival of the useful cells?
The first checkpoint in B and T cell maturation involves the selection of pre-B and pre-T cells that have productively rearranged the µ heavy-chain gene in the case of B lineage cells and the TCR β chain gene in the case of developing T cells. Positive selection is a process in which T cells that can recognize self MHC molecules weakly are allowed to survive and express the type of co-receptor that matches the type of MHC molecule recognized.
What is the phenomenon of negative selection, and what is its importance?
Negative selection results in the deletion or editing of strongly self-reactive lymphocytes. This process mediates self tolerance in the thymus for T cells and in the bone marrow for B cells.
