1. Several types of pathogens encode proteins that function as superantigens, wh
ID: 204082 • Letter: 1
Question
1. Several types of pathogens encode proteins that function as superantigens, which activate massive numbers of T cells in an individual. One example is the staphylococcal enterotoxins that cause food poisoning. These superantigens are the exception to the general rule that T cells only recognize specific peptide:MHC complexes, because they:
A. Induce activation of any T cell whose T-cell receptor uses a particular V region bound by that superantigen
B. Simultaneously stimulate all of the T-cell receptors on a given T cell
C. Cover up the peptide-binding site, preventing MHC molecules from binding peptides
D. Activate a large number of T cells that are specifically recognizing peptides derived from the superantigen protein
E. Induce anti-microbial cytokine production that aids the immune system in clearing the pathogen
2. The extensive polymorphism of MHC genes in the population is thought to represent an evolutionary response to outflank the evasive strategies of pathogens. This polymorphism makes it difficult for pathogens to eliminate all potential MHC binding epitopes from their proteins. Based on this reasoning, it would seem advantageous for each individual to encode more than three different MHC class I and three different MHC class II genes per chromosome copy. If some individuals in the population had MHC loci that encoded 10 different MHC class I and 10 different MHC class II genes, the T cell repertoire in those individuals would likely be:
A. Much more diverse than in the rest of the individuals of that population
B. Much better at recognizing rare pathogens not encountered by most individuals in that population
C. Much less diverse than the rest of the individuals in that population
D. Much more alloreactive than the T cells found in the other individuals of that population
E. Very reactive to bacterial and viral superantigens
3. T cells expressing gamma:delta T-cell receptors have been found to recognizea diversity of ligands, including pathogen-derived proteins, self-peptides, and stress-induced molecules. This pattern of antigen recognition shows similarity to that of iNKT cells and MAIT cells,suggesting that gamma:delta T cells:
A. Do not play an important role in immunity, but likely have a non-immune function
B. Share features of both innate and adaptive immune cells
C. Are only able to respond when the host is infected with a virus such as herpes simplex virus
D. Are involved in maintaining the integrity of endothelial cells in the host
E. Are most important in responses to tumor cells that show stress responses
Explanation / Answer
1- A
Superantigen bind at a lateral site on TCR ,Vb region and hence activates a large number of t cells.
2- B
Since the type of mhc complexes increases , it would be able to bind different kind of pathogens , hence They are better at recognizing rare proteins.
3- B
These t cells recognize peptide , sugar and lipid antigens at epithelium of skin and mucosa and fight against microbes trying to invade . they dont require MHC for killing like alpha beta T cells, thereby functioning like innate immunity cells.
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