Question

If the process of positive selection did not occur, then

a. a condition resembling immune dysregulation, polyendocrinopathy, enteropathy, X-linked syndrome (IPEX) would develop
b. a condition resembling autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED) would develop
c. naive T cells would be unable to undergo differentiation in secondary lymphoid tissues
d. malignant transformation would be more likely because of the accumulation of multiple mutations
e. only a very small percentage of circulating T lymphocytes would be able to become activated.

Answer 1

Without positive selection in T-cell development, only a very small percentage of circulating T lymphocytes would be able to become activated, significantly compromising the immune system.

Step-by-step explanation:

If the process of positive selection did not occur in T-cell development, the most likely outcome would be that only a very small percentage of circulating T lymphocytes would be able to become activated (choice e). During thymic selection, thymocytes are exposed to cortical epithelial cells within the thymus. This exposure leads to the process of positive selection where thymocytes that successfully bind to self Major Histocompatibility Complex (MHC) molecules are stimulated to mature further. On the other hand, thymocytes that fail to interact appropriately are not stimulated and are eliminated by apoptosis. This selection ensures that mature T cells can recognize self-MHC molecules presented with foreign antigens and become activated in response to these antigens. Without positive selection, most thymocytes would fail to develop into functional T cells, drastically reducing the population of T cells that can respond to antigen presentation and effectively leaving the body without a proper immune surveillance and response system.

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